XFA: Upgrade libpng to 1.6.20.

third_party/lpng_v163/pngrtran.c

-/* pngrtran.c - transforms the data in a row for PNG readers
- *
- * Last changed in libpng 1.6.2 [April 25, 2013]
- * Copyright (c) 1998-2013 Glenn Randers-Pehrson
- * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
- * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
- *
- * This code is released under the libpng license.
- * For conditions of distribution and use, see the disclaimer
- * and license in png.h
- *
- * This file contains functions optionally called by an application
- * in order to tell libpng how to handle data when reading a PNG.
- * Transformations that are used in both reading and writing are
- * in pngtrans.c.
- */
-
-#include "pngpriv.h"
-
-#ifdef PNG_READ_SUPPORTED
-
-/* Set the action on getting a CRC error for an ancillary or critical chunk. */
-void PNGAPI
-png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
-{
-   png_debug(1, "in png_set_crc_action");
-
-   if (png_ptr == NULL)
-      return;
-
-   /* Tell libpng how we react to CRC errors in critical chunks */
-   switch (crit_action)
-   {
-      case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
-         break;
-
-      case PNG_CRC_WARN_USE:                               /* Warn/use data */
-         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
-         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
-         break;
-
-      case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
-         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
-         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
-                           PNG_FLAG_CRC_CRITICAL_IGNORE;
-         break;
-
-      case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
-         png_warning(png_ptr,
-            "Can't discard critical data on CRC error");
-      case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
-
-      case PNG_CRC_DEFAULT:
-      default:
-         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
-         break;
-   }
-
-   /* Tell libpng how we react to CRC errors in ancillary chunks */
-   switch (ancil_action)
-   {
-      case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
-         break;
-
-      case PNG_CRC_WARN_USE:                              /* Warn/use data */
-         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
-         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
-         break;
-
-      case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
-         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
-         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
-                           PNG_FLAG_CRC_ANCILLARY_NOWARN;
-         break;
-
-      case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
-         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
-         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
-         break;
-
-      case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */
-
-      case PNG_CRC_DEFAULT:
-      default:
-         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
-         break;
-   }
-}
-
-#ifdef PNG_READ_TRANSFORMS_SUPPORTED
-/* Is it OK to set a transformation now?  Only if png_start_read_image or
- * png_read_update_info have not been called.  It is not necessary for the IHDR
- * to have been read in all cases, the parameter allows for this check too.
- */
-static int
-png_rtran_ok(png_structrp png_ptr, int need_IHDR)
-{
-   if (png_ptr != NULL)
-   {
-      if (png_ptr->flags & PNG_FLAG_ROW_INIT)
-         png_app_error(png_ptr,
-            "invalid after png_start_read_image or png_read_update_info");
-
-      else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
-         png_app_error(png_ptr, "invalid before the PNG header has been read");
-
-      else
-      {
-         /* Turn on failure to initialize correctly for all transforms. */
-         png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
-
-         return 1; /* Ok */
-      }
-   }
-
-   return 0; /* no png_error possible! */
-}
-#endif
-
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-/* Handle alpha and tRNS via a background color */
-void PNGFAPI
-png_set_background_fixed(png_structrp png_ptr,
-    png_const_color_16p background_color, int background_gamma_code,
-    int need_expand, png_fixed_point background_gamma)
-{
-   png_debug(1, "in png_set_background_fixed");
-
-   if (!png_rtran_ok(png_ptr, 0) || background_color == NULL)
-      return;
-
-   if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
-   {
-      png_warning(png_ptr, "Application must supply a known background gamma");
-      return;
-   }
-
-   png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
-   png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-   png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-
-   png_ptr->background = *background_color;
-   png_ptr->background_gamma = background_gamma;
-   png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
-   if (need_expand)
-      png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
-   else
-      png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
-}
-
-#  ifdef PNG_FLOATING_POINT_SUPPORTED
-void PNGAPI
-png_set_background(png_structrp png_ptr,
-    png_const_color_16p background_color, int background_gamma_code,
-    int need_expand, double background_gamma)
-{
-   png_set_background_fixed(png_ptr, background_color, background_gamma_code,
-      need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
-}
-#  endif  /* FLOATING_POINT */
-#endif /* READ_BACKGROUND */
-
-/* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
- * one that pngrtran does first (scale) happens.  This is necessary to allow the
- * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
- */
-#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
-void PNGAPI
-png_set_scale_16(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_scale_16");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= PNG_SCALE_16_TO_8;
-}
-#endif
-
-#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
-/* Chop 16-bit depth files to 8-bit depth */
-void PNGAPI
-png_set_strip_16(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_strip_16");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= PNG_16_TO_8;
-}
-#endif
-
-#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
-void PNGAPI
-png_set_strip_alpha(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_strip_alpha");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= PNG_STRIP_ALPHA;
-}
-#endif
-
-#if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
-static png_fixed_point
-translate_gamma_flags(png_structrp png_ptr, png_fixed_point output_gamma,
-   int is_screen)
-{
-   /* Check for flag values.  The main reason for having the old Mac value as a
-    * flag is that it is pretty near impossible to work out what the correct
-    * value is from Apple documentation - a working Mac system is needed to
-    * discover the value!
-    */
-   if (output_gamma == PNG_DEFAULT_sRGB ||
-      output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
-   {
-      /* If there is no sRGB support this just sets the gamma to the standard
-       * sRGB value.  (This is a side effect of using this function!)
-       */
-#     ifdef PNG_READ_sRGB_SUPPORTED
-         png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
-#     else
-         PNG_UNUSED(png_ptr)
-#     endif
-      if (is_screen)
-         output_gamma = PNG_GAMMA_sRGB;
-      else
-         output_gamma = PNG_GAMMA_sRGB_INVERSE;
-   }
-
-   else if (output_gamma == PNG_GAMMA_MAC_18 ||
-      output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
-   {
-      if (is_screen)
-         output_gamma = PNG_GAMMA_MAC_OLD;
-      else
-         output_gamma = PNG_GAMMA_MAC_INVERSE;
-   }
-
-   return output_gamma;
-}
-
-#  ifdef PNG_FLOATING_POINT_SUPPORTED
-static png_fixed_point
-convert_gamma_value(png_structrp png_ptr, double output_gamma)
-{
-   /* The following silently ignores cases where fixed point (times 100,000)
-    * gamma values are passed to the floating point API.  This is safe and it
-    * means the fixed point constants work just fine with the floating point
-    * API.  The alternative would just lead to undetected errors and spurious
-    * bug reports.  Negative values fail inside the _fixed API unless they
-    * correspond to the flag values.
-    */
-   if (output_gamma > 0 && output_gamma < 128)
-      output_gamma *= PNG_FP_1;
-
-   /* This preserves -1 and -2 exactly: */
-   output_gamma = floor(output_gamma + .5);
-
-   if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
-      png_fixed_error(png_ptr, "gamma value");
-
-   return (png_fixed_point)output_gamma;
-}
-#  endif
-#endif /* READ_ALPHA_MODE || READ_GAMMA */
-
-#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
-void PNGFAPI
-png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
-   png_fixed_point output_gamma)
-{
-   int compose = 0;
-   png_fixed_point file_gamma;
-
-   png_debug(1, "in png_set_alpha_mode");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
-
-   /* Validate the value to ensure it is in a reasonable range. The value
-    * is expected to be 1 or greater, but this range test allows for some
-    * viewing correction values.  The intent is to weed out users of this API
-    * who use the inverse of the gamma value accidentally!  Since some of these
-    * values are reasonable this may have to be changed.
-    */
-   if (output_gamma < 70000 || output_gamma > 300000)
-      png_error(png_ptr, "output gamma out of expected range");
-
-   /* The default file gamma is the inverse of the output gamma; the output
-    * gamma may be changed below so get the file value first:
-    */
-   file_gamma = png_reciprocal(output_gamma);
-
-   /* There are really 8 possibilities here, composed of any combination
-    * of:
-    *
-    *    premultiply the color channels
-    *    do not encode non-opaque pixels
-    *    encode the alpha as well as the color channels
-    *
-    * The differences disappear if the input/output ('screen') gamma is 1.0,
-    * because then the encoding is a no-op and there is only the choice of
-    * premultiplying the color channels or not.
-    *
-    * png_set_alpha_mode and png_set_background interact because both use
-    * png_compose to do the work.  Calling both is only useful when
-    * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
-    * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
-    */
-   switch (mode)
-   {
-      case PNG_ALPHA_PNG:        /* default: png standard */
-         /* No compose, but it may be set by png_set_background! */
-         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-         break;
-
-      case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
-         compose = 1;
-         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-         /* The output is linear: */
-         output_gamma = PNG_FP_1;
-         break;
-
-      case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
-         compose = 1;
-         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-         png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
-         /* output_gamma records the encoding of opaque pixels! */
-         break;
-
-      case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
-         compose = 1;
-         png_ptr->transformations |= PNG_ENCODE_ALPHA;
-         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-         break;
-
-      default:
-         png_error(png_ptr, "invalid alpha mode");
-   }
-
-   /* Only set the default gamma if the file gamma has not been set (this has
-    * the side effect that the gamma in a second call to png_set_alpha_mode will
-    * be ignored.)
-    */
-   if (png_ptr->colorspace.gamma == 0)
-   {
-      png_ptr->colorspace.gamma = file_gamma;
-      png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
-   }
-
-   /* But always set the output gamma: */
-   png_ptr->screen_gamma = output_gamma;
-
-   /* Finally, if pre-multiplying, set the background fields to achieve the
-    * desired result.
-    */
-   if (compose)
-   {
-      /* And obtain alpha pre-multiplication by composing on black: */
-      memset(&png_ptr->background, 0, (sizeof png_ptr->background));
-      png_ptr->background_gamma = png_ptr->colorspace.gamma; /* just in case */
-      png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
-      png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
-
-      if (png_ptr->transformations & PNG_COMPOSE)
-         png_error(png_ptr,
-            "conflicting calls to set alpha mode and background");
-
-      png_ptr->transformations |= PNG_COMPOSE;
-   }
-}
-
-#  ifdef PNG_FLOATING_POINT_SUPPORTED
-void PNGAPI
-png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
-{
-   png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
-      output_gamma));
-}
-#  endif
-#endif
-
-#ifdef PNG_READ_QUANTIZE_SUPPORTED
-/* Dither file to 8-bit.  Supply a palette, the current number
- * of elements in the palette, the maximum number of elements
- * allowed, and a histogram if possible.  If the current number
- * of colors is greater then the maximum number, the palette will be
- * modified to fit in the maximum number.  "full_quantize" indicates
- * whether we need a quantizing cube set up for RGB images, or if we
- * simply are reducing the number of colors in a paletted image.
- */
-
-typedef struct png_dsort_struct
-{
-   struct png_dsort_struct * next;
-   png_byte left;
-   png_byte right;
-} png_dsort;
-typedef png_dsort *   png_dsortp;
-typedef png_dsort * * png_dsortpp;
-
-void PNGAPI
-png_set_quantize(png_structrp png_ptr, png_colorp palette,
-    int num_palette, int maximum_colors, png_const_uint_16p histogram,
-    int full_quantize)
-{
-   png_debug(1, "in png_set_quantize");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= PNG_QUANTIZE;
-
-   if (!full_quantize)
-   {
-      int i;
-
-      png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
-          (png_uint_32)(num_palette * (sizeof (png_byte))));
-      for (i = 0; i < num_palette; i++)
-         png_ptr->quantize_index[i] = (png_byte)i;
-   }
-
-   if (num_palette > maximum_colors)
-   {
-      if (histogram != NULL)
-      {
-         /* This is easy enough, just throw out the least used colors.
-          * Perhaps not the best solution, but good enough.
-          */
-
-         int i;
-
-         /* Initialize an array to sort colors */
-         png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * (sizeof (png_byte))));
-
-         /* Initialize the quantize_sort array */
-         for (i = 0; i < num_palette; i++)
-            png_ptr->quantize_sort[i] = (png_byte)i;
-
-         /* Find the least used palette entries by starting a
-          * bubble sort, and running it until we have sorted
-          * out enough colors.  Note that we don't care about
-          * sorting all the colors, just finding which are
-          * least used.
-          */
-
-         for (i = num_palette - 1; i >= maximum_colors; i--)
-         {
-            int done; /* To stop early if the list is pre-sorted */
-            int j;
-
-            done = 1;
-            for (j = 0; j < i; j++)
-            {
-               if (histogram[png_ptr->quantize_sort[j]]
-                   < histogram[png_ptr->quantize_sort[j + 1]])
-               {
-                  png_byte t;
-
-                  t = png_ptr->quantize_sort[j];
-                  png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
-                  png_ptr->quantize_sort[j + 1] = t;
-                  done = 0;
-               }
-            }
-
-            if (done)
-               break;
-         }
-
-         /* Swap the palette around, and set up a table, if necessary */
-         if (full_quantize)
-         {
-            int j = num_palette;
-
-            /* Put all the useful colors within the max, but don't
-             * move the others.
-             */
-            for (i = 0; i < maximum_colors; i++)
-            {
-               if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
-               {
-                  do
-                     j--;
-                  while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
-
-                  palette[i] = palette[j];
-               }
-            }
-         }
-         else
-         {
-            int j = num_palette;
-
-            /* Move all the used colors inside the max limit, and
-             * develop a translation table.
-             */
-            for (i = 0; i < maximum_colors; i++)
-            {
-               /* Only move the colors we need to */
-               if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
-               {
-                  png_color tmp_color;
-
-                  do
-                     j--;
-                  while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
-
-                  tmp_color = palette[j];
-                  palette[j] = palette[i];
-                  palette[i] = tmp_color;
-                  /* Indicate where the color went */
-                  png_ptr->quantize_index[j] = (png_byte)i;
-                  png_ptr->quantize_index[i] = (png_byte)j;
-               }
-            }
-
-            /* Find closest color for those colors we are not using */
-            for (i = 0; i < num_palette; i++)
-            {
-               if ((int)png_ptr->quantize_index[i] >= maximum_colors)
-               {
-                  int min_d, k, min_k, d_index;
-
-                  /* Find the closest color to one we threw out */
-                  d_index = png_ptr->quantize_index[i];
-                  min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
-                  for (k = 1, min_k = 0; k < maximum_colors; k++)
-                  {
-                     int d;
-
-                     d = PNG_COLOR_DIST(palette[d_index], palette[k]);
-
-                     if (d < min_d)
-                     {
-                        min_d = d;
-                        min_k = k;
-                     }
-                  }
-                  /* Point to closest color */
-                  png_ptr->quantize_index[i] = (png_byte)min_k;
-               }
-            }
-         }
-         png_free(png_ptr, png_ptr->quantize_sort);
-         png_ptr->quantize_sort = NULL;
-      }
-      else
-      {
-         /* This is much harder to do simply (and quickly).  Perhaps
-          * we need to go through a median cut routine, but those
-          * don't always behave themselves with only a few colors
-          * as input.  So we will just find the closest two colors,
-          * and throw out one of them (chosen somewhat randomly).
-          * [We don't understand this at all, so if someone wants to
-          *  work on improving it, be our guest - AED, GRP]
-          */
-         int i;
-         int max_d;
-         int num_new_palette;
-         png_dsortp t;
-         png_dsortpp hash;
-
-         t = NULL;
-
-         /* Initialize palette index arrays */
-         png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * (sizeof (png_byte))));
-         png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
-             (png_uint_32)(num_palette * (sizeof (png_byte))));
-
-         /* Initialize the sort array */
-         for (i = 0; i < num_palette; i++)
-         {
-            png_ptr->index_to_palette[i] = (png_byte)i;
-            png_ptr->palette_to_index[i] = (png_byte)i;
-         }
-
-         hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
-             (sizeof (png_dsortp))));
-
-         num_new_palette = num_palette;
-
-         /* Initial wild guess at how far apart the farthest pixel
-          * pair we will be eliminating will be.  Larger
-          * numbers mean more areas will be allocated, Smaller
-          * numbers run the risk of not saving enough data, and
-          * having to do this all over again.
-          *
-          * I have not done extensive checking on this number.
-          */
-         max_d = 96;
-
-         while (num_new_palette > maximum_colors)
-         {
-            for (i = 0; i < num_new_palette - 1; i++)
-            {
-               int j;
-
-               for (j = i + 1; j < num_new_palette; j++)
-               {
-                  int d;
-
-                  d = PNG_COLOR_DIST(palette[i], palette[j]);
-
-                  if (d <= max_d)
-                  {
-
-                     t = (png_dsortp)png_malloc_warn(png_ptr,
-                         (png_uint_32)(sizeof (png_dsort)));
-
-                     if (t == NULL)
-                         break;
-
-                     t->next = hash[d];
-                     t->left = (png_byte)i;
-                     t->right = (png_byte)j;
-                     hash[d] = t;
-                  }
-               }
-               if (t == NULL)
-                  break;
-            }
-
-            if (t != NULL)
-            for (i = 0; i <= max_d; i++)
-            {
-               if (hash[i] != NULL)
-               {
-                  png_dsortp p;
-
-                  for (p = hash[i]; p; p = p->next)
-                  {
-                     if ((int)png_ptr->index_to_palette[p->left]
-                         < num_new_palette &&
-                         (int)png_ptr->index_to_palette[p->right]
-                         < num_new_palette)
-                     {
-                        int j, next_j;
-
-                        if (num_new_palette & 0x01)
-                        {
-                           j = p->left;
-                           next_j = p->right;
-                        }
-                        else
-                        {
-                           j = p->right;
-                           next_j = p->left;
-                        }
-
-                        num_new_palette--;
-                        palette[png_ptr->index_to_palette[j]]
-                            = palette[num_new_palette];
-                        if (!full_quantize)
-                        {
-                           int k;
-
-                           for (k = 0; k < num_palette; k++)
-                           {
-                              if (png_ptr->quantize_index[k] ==
-                                  png_ptr->index_to_palette[j])
-                                 png_ptr->quantize_index[k] =
-                                     png_ptr->index_to_palette[next_j];
-
-                              if ((int)png_ptr->quantize_index[k] ==
-                                  num_new_palette)
-                                 png_ptr->quantize_index[k] =
-                                     png_ptr->index_to_palette[j];
-                           }
-                        }
-
-                        png_ptr->index_to_palette[png_ptr->palette_to_index
-                            [num_new_palette]] = png_ptr->index_to_palette[j];
-
-                        png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
-                            = png_ptr->palette_to_index[num_new_palette];
-
-                        png_ptr->index_to_palette[j] =
-                            (png_byte)num_new_palette;
-
-                        png_ptr->palette_to_index[num_new_palette] =
-                            (png_byte)j;
-                     }
-                     if (num_new_palette <= maximum_colors)
-                        break;
-                  }
-                  if (num_new_palette <= maximum_colors)
-                     break;
-               }
-            }
-
-            for (i = 0; i < 769; i++)
-            {
-               if (hash[i] != NULL)
-               {
-                  png_dsortp p = hash[i];
-                  while (p)
-                  {
-                     t = p->next;
-                     png_free(png_ptr, p);
-                     p = t;
-                  }
-               }
-               hash[i] = 0;
-            }
-            max_d += 96;
-         }
-         png_free(png_ptr, hash);
-         png_free(png_ptr, png_ptr->palette_to_index);
-         png_free(png_ptr, png_ptr->index_to_palette);
-         png_ptr->palette_to_index = NULL;
-         png_ptr->index_to_palette = NULL;
-      }
-      num_palette = maximum_colors;
-   }
-   if (png_ptr->palette == NULL)
-   {
-      png_ptr->palette = palette;
-   }
-   png_ptr->num_palette = (png_uint_16)num_palette;
-
-   if (full_quantize)
-   {
-      int i;
-      png_bytep distance;
-      int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
-          PNG_QUANTIZE_BLUE_BITS;
-      int num_red = (1 << PNG_QUANTIZE_RED_BITS);
-      int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
-      int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
-      png_size_t num_entries = ((png_size_t)1 << total_bits);
-
-      png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
-          (png_uint_32)(num_entries * (sizeof (png_byte))));
-
-      distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
-          (sizeof (png_byte))));
-
-      memset(distance, 0xff, num_entries * (sizeof (png_byte)));
-
-      for (i = 0; i < num_palette; i++)
-      {
-         int ir, ig, ib;
-         int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
-         int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
-         int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
-
-         for (ir = 0; ir < num_red; ir++)
-         {
-            /* int dr = abs(ir - r); */
-            int dr = ((ir > r) ? ir - r : r - ir);
-            int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
-                PNG_QUANTIZE_GREEN_BITS));
-
-            for (ig = 0; ig < num_green; ig++)
-            {
-               /* int dg = abs(ig - g); */
-               int dg = ((ig > g) ? ig - g : g - ig);
-               int dt = dr + dg;
-               int dm = ((dr > dg) ? dr : dg);
-               int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
-
-               for (ib = 0; ib < num_blue; ib++)
-               {
-                  int d_index = index_g | ib;
-                  /* int db = abs(ib - b); */
-                  int db = ((ib > b) ? ib - b : b - ib);
-                  int dmax = ((dm > db) ? dm : db);
-                  int d = dmax + dt + db;
-
-                  if (d < (int)distance[d_index])
-                  {
-                     distance[d_index] = (png_byte)d;
-                     png_ptr->palette_lookup[d_index] = (png_byte)i;
-                  }
-               }
-            }
-         }
-      }
-
-      png_free(png_ptr, distance);
-   }
-}
-#endif /* PNG_READ_QUANTIZE_SUPPORTED */
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-void PNGFAPI
-png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
-   png_fixed_point file_gamma)
-{
-   png_debug(1, "in png_set_gamma_fixed");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   /* New in libpng-1.5.4 - reserve particular negative values as flags. */
-   scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
-   file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
-
-   /* Checking the gamma values for being >0 was added in 1.5.4 along with the
-    * premultiplied alpha support; this actually hides an undocumented feature
-    * of the previous implementation which allowed gamma processing to be
-    * disabled in background handling.  There is no evidence (so far) that this
-    * was being used; however, png_set_background itself accepted and must still
-    * accept '0' for the gamma value it takes, because it isn't always used.
-    *
-    * Since this is an API change (albeit a very minor one that removes an
-    * undocumented API feature) the following checks were only enabled in
-    * libpng-1.6.0.
-    */
-   if (file_gamma <= 0)
-      png_error(png_ptr, "invalid file gamma in png_set_gamma");
-
-   if (scrn_gamma <= 0)
-      png_error(png_ptr, "invalid screen gamma in png_set_gamma");
-
-   /* Set the gamma values unconditionally - this overrides the value in the PNG
-    * file if a gAMA chunk was present.  png_set_alpha_mode provides a
-    * different, easier, way to default the file gamma.
-    */
-   png_ptr->colorspace.gamma = file_gamma;
-   png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
-   png_ptr->screen_gamma = scrn_gamma;
-}
-
-#  ifdef PNG_FLOATING_POINT_SUPPORTED
-void PNGAPI
-png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
-{
-   png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
-      convert_gamma_value(png_ptr, file_gamma));
-}
-#  endif /* FLOATING_POINT_SUPPORTED */
-#endif /* READ_GAMMA */
-
-#ifdef PNG_READ_EXPAND_SUPPORTED
-/* Expand paletted images to RGB, expand grayscale images of
- * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
- * to alpha channels.
- */
-void PNGAPI
-png_set_expand(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_expand");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
-}
-
-/* GRR 19990627:  the following three functions currently are identical
- *  to png_set_expand().  However, it is entirely reasonable that someone
- *  might wish to expand an indexed image to RGB but *not* expand a single,
- *  fully transparent palette entry to a full alpha channel--perhaps instead
- *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
- *  the transparent color with a particular RGB value, or drop tRNS entirely.
- *  IOW, a future version of the library may make the transformations flag
- *  a bit more fine-grained, with separate bits for each of these three
- *  functions.
- *
- *  More to the point, these functions make it obvious what libpng will be
- *  doing, whereas "expand" can (and does) mean any number of things.
- *
- *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
- *  to expand only the sample depth but not to expand the tRNS to alpha
- *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
- */
-
-/* Expand paletted images to RGB. */
-void PNGAPI
-png_set_palette_to_rgb(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_palette_to_rgb");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
-}
-
-/* Expand grayscale images of less than 8-bit depth to 8 bits. */
-void PNGAPI
-png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= PNG_EXPAND;
-}
-
-/* Expand tRNS chunks to alpha channels. */
-void PNGAPI
-png_set_tRNS_to_alpha(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_tRNS_to_alpha");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
-}
-#endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
-
-#ifdef PNG_READ_EXPAND_16_SUPPORTED
-/* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
- * it may not work correctly.)
- */
-void PNGAPI
-png_set_expand_16(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_expand_16");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
-}
-#endif
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-void PNGAPI
-png_set_gray_to_rgb(png_structrp png_ptr)
-{
-   png_debug(1, "in png_set_gray_to_rgb");
-
-   if (!png_rtran_ok(png_ptr, 0))
-      return;
-
-   /* Because rgb must be 8 bits or more: */
-   png_set_expand_gray_1_2_4_to_8(png_ptr);
-   png_ptr->transformations |= PNG_GRAY_TO_RGB;
-}
-#endif
-
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-void PNGFAPI
-png_set_rgb_to_gray_fixed(png_structrp png_ptr, int error_action,
-    png_fixed_point red, png_fixed_point green)
-{
-   png_debug(1, "in png_set_rgb_to_gray");
-
-   /* Need the IHDR here because of the check on color_type below. */
-   /* TODO: fix this */
-   if (!png_rtran_ok(png_ptr, 1))
-      return;
-
-   switch(error_action)
-   {
-      case PNG_ERROR_ACTION_NONE:
-         png_ptr->transformations |= PNG_RGB_TO_GRAY;
-         break;
-
-      case PNG_ERROR_ACTION_WARN:
-         png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
-         break;
-
-      case PNG_ERROR_ACTION_ERROR:
-         png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
-         break;
-
-      default:
-         png_error(png_ptr, "invalid error action to rgb_to_gray");
-         break;
-   }
-
-   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-#ifdef PNG_READ_EXPAND_SUPPORTED
-      png_ptr->transformations |= PNG_EXPAND;
-#else
-   {
-      /* Make this an error in 1.6 because otherwise the application may assume
-       * that it just worked and get a memory overwrite.
-       */
-      png_error(png_ptr,
-        "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");
-
-      /* png_ptr->transformations &= ~PNG_RGB_TO_GRAY; */
-   }
-#endif
-   {
-      if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
-      {
-         png_uint_16 red_int, green_int;
-
-         /* NOTE: this calculation does not round, but this behavior is retained
-          * for consistency, the inaccuracy is very small.  The code here always
-          * overwrites the coefficients, regardless of whether they have been
-          * defaulted or set already.
-          */
-         red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
-         green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);
-
-         png_ptr->rgb_to_gray_red_coeff   = red_int;
-         png_ptr->rgb_to_gray_green_coeff = green_int;
-         png_ptr->rgb_to_gray_coefficients_set = 1;
-      }
-
-      else
-      {
-         if (red >= 0 && green >= 0)
-            png_app_warning(png_ptr,
-               "ignoring out of range rgb_to_gray coefficients");
-
-         /* Use the defaults, from the cHRM chunk if set, else the historical
-          * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
-          * png_do_rgb_to_gray for more discussion of the values.  In this case
-          * the coefficients are not marked as 'set' and are not overwritten if
-          * something has already provided a default.
-          */
-         if (png_ptr->rgb_to_gray_red_coeff == 0 &&
-            png_ptr->rgb_to_gray_green_coeff == 0)
-         {
-            png_ptr->rgb_to_gray_red_coeff   = 6968;
-            png_ptr->rgb_to_gray_green_coeff = 23434;
-            /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
-         }
-      }
-   }
-}
-
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-/* Convert a RGB image to a grayscale of the same width.  This allows us,
- * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
- */
-
-void PNGAPI
-png_set_rgb_to_gray(png_structrp png_ptr, int error_action, double red,
-   double green)
-{
-   png_set_rgb_to_gray_fixed(png_ptr, error_action,
-      png_fixed(png_ptr, red, "rgb to gray red coefficient"),
-      png_fixed(png_ptr, green, "rgb to gray green coefficient"));
-}
-#endif /* FLOATING POINT */
-
-#endif /* RGB_TO_GRAY */
-
-#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
-    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
-void PNGAPI
-png_set_read_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
-    read_user_transform_fn)
-{
-   png_debug(1, "in png_set_read_user_transform_fn");
-
-#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
-   png_ptr->transformations |= PNG_USER_TRANSFORM;
-   png_ptr->read_user_transform_fn = read_user_transform_fn;
-#endif
-}
-#endif
-
-#ifdef PNG_READ_TRANSFORMS_SUPPORTED
-#ifdef PNG_READ_GAMMA_SUPPORTED
-/* In the case of gamma transformations only do transformations on images where
- * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
- * slows things down slightly, and also needlessly introduces small errors.
- */
-static int /* PRIVATE */
-png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
-{
-   /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
-    * correction as a difference of the overall transform from 1.0
-    *
-    * We want to compare the threshold with s*f - 1, if we get
-    * overflow here it is because of wacky gamma values so we
-    * turn on processing anyway.
-    */
-   png_fixed_point gtest;
-   return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
-       png_gamma_significant(gtest);
-}
-#endif
-
-/* Initialize everything needed for the read.  This includes modifying
- * the palette.
- */
-
-/*For the moment 'png_init_palette_transformations' and
- * 'png_init_rgb_transformations' only do some flag canceling optimizations.
- * The intent is that these two routines should have palette or rgb operations
- * extracted from 'png_init_read_transformations'.
- */
-static void /* PRIVATE */
-png_init_palette_transformations(png_structrp png_ptr)
-{
-   /* Called to handle the (input) palette case.  In png_do_read_transformations
-    * the first step is to expand the palette if requested, so this code must
-    * take care to only make changes that are invariant with respect to the
-    * palette expansion, or only do them if there is no expansion.
-    *
-    * STRIP_ALPHA has already been handled in the caller (by setting num_trans
-    * to 0.)
-    */
-   int input_has_alpha = 0;
-   int input_has_transparency = 0;
-
-   if (png_ptr->num_trans > 0)
-   {
-      int i;
-
-      /* Ignore if all the entries are opaque (unlikely!) */
-      for (i=0; i<png_ptr->num_trans; ++i)
-         if (png_ptr->trans_alpha[i] == 255)
-            continue;
-         else if (png_ptr->trans_alpha[i] == 0)
-            input_has_transparency = 1;
-         else
-            input_has_alpha = 1;
-   }
-
-   /* If no alpha we can optimize. */
-   if (!input_has_alpha)
-   {
-      /* Any alpha means background and associative alpha processing is
-       * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
-       * and ENCODE_ALPHA are irrelevant.
-       */
-      png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-
-      if (!input_has_transparency)
-         png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
-   }
-
-#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
-   /* png_set_background handling - deals with the complexity of whether the
-    * background color is in the file format or the screen format in the case
-    * where an 'expand' will happen.
-    */
-
-   /* The following code cannot be entered in the alpha pre-multiplication case
-    * because PNG_BACKGROUND_EXPAND is cancelled below.
-    */
-   if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
-       (png_ptr->transformations & PNG_EXPAND))
-   {
-      {
-         png_ptr->background.red   =
-             png_ptr->palette[png_ptr->background.index].red;
-         png_ptr->background.green =
-             png_ptr->palette[png_ptr->background.index].green;
-         png_ptr->background.blue  =
-             png_ptr->palette[png_ptr->background.index].blue;
-
-#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
-        if (png_ptr->transformations & PNG_INVERT_ALPHA)
-        {
-           if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
-           {
-              /* Invert the alpha channel (in tRNS) unless the pixels are
-               * going to be expanded, in which case leave it for later
-               */
-              int i, istop = png_ptr->num_trans;
-
-              for (i=0; i<istop; i++)
-                 png_ptr->trans_alpha[i] = (png_byte)(255 -
-                    png_ptr->trans_alpha[i]);
-           }
-        }
-#endif /* PNG_READ_INVERT_ALPHA_SUPPORTED */
-      }
-   } /* background expand and (therefore) no alpha association. */
-#endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
-}
-
-static void /* PRIVATE */
-png_init_rgb_transformations(png_structrp png_ptr)
-{
-   /* Added to libpng-1.5.4: check the color type to determine whether there
-    * is any alpha or transparency in the image and simply cancel the
-    * background and alpha mode stuff if there isn't.
-    */
-   int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
-   int input_has_transparency = png_ptr->num_trans > 0;
-
-   /* If no alpha we can optimize. */
-   if (!input_has_alpha)
-   {
-      /* Any alpha means background and associative alpha processing is
-       * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
-       * and ENCODE_ALPHA are irrelevant.
-       */
-#     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
-         png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-         png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-#     endif
-
-      if (!input_has_transparency)
-         png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
-   }
-
-#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
-   /* png_set_background handling - deals with the complexity of whether the
-    * background color is in the file format or the screen format in the case
-    * where an 'expand' will happen.
-    */
-
-   /* The following code cannot be entered in the alpha pre-multiplication case
-    * because PNG_BACKGROUND_EXPAND is cancelled below.
-    */
-   if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
-       (png_ptr->transformations & PNG_EXPAND) &&
-       !(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
-       /* i.e., GRAY or GRAY_ALPHA */
-   {
-      {
-         /* Expand background and tRNS chunks */
-         int gray = png_ptr->background.gray;
-         int trans_gray = png_ptr->trans_color.gray;
-
-         switch (png_ptr->bit_depth)
-         {
-            case 1:
-               gray *= 0xff;
-               trans_gray *= 0xff;
-               break;
-
-            case 2:
-               gray *= 0x55;
-               trans_gray *= 0x55;
-               break;
-
-            case 4:
-               gray *= 0x11;
-               trans_gray *= 0x11;
-               break;
-
-            default:
-
-            case 8:
-               /* FALL THROUGH (Already 8 bits) */
-
-            case 16:
-               /* Already a full 16 bits */
-               break;
-         }
-
-         png_ptr->background.red = png_ptr->background.green =
-            png_ptr->background.blue = (png_uint_16)gray;
-
-         if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
-         {
-            png_ptr->trans_color.red = png_ptr->trans_color.green =
-               png_ptr->trans_color.blue = (png_uint_16)trans_gray;
-         }
-      }
-   } /* background expand and (therefore) no alpha association. */
-#endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
-}
-
-void /* PRIVATE */
-png_init_read_transformations(png_structrp png_ptr)
-{
-   png_debug(1, "in png_init_read_transformations");
-
-   /* This internal function is called from png_read_start_row in pngrutil.c
-    * and it is called before the 'rowbytes' calculation is done, so the code
-    * in here can change or update the transformations flags.
-    *
-    * First do updates that do not depend on the details of the PNG image data
-    * being processed.
-    */
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
-    * png_set_alpha_mode and this is another source for a default file gamma so
-    * the test needs to be performed later - here.  In addition prior to 1.5.4
-    * the tests were repeated for the PALETTE color type here - this is no
-    * longer necessary (and doesn't seem to have been necessary before.)
-    */
-   {
-      /* The following temporary indicates if overall gamma correction is
-       * required.
-       */
-      int gamma_correction = 0;
-
-      if (png_ptr->colorspace.gamma != 0) /* has been set */
-      {
-         if (png_ptr->screen_gamma != 0) /* screen set too */
-            gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
-               png_ptr->screen_gamma);
-
-         else
-            /* Assume the output matches the input; a long time default behavior
-             * of libpng, although the standard has nothing to say about this.
-             */
-            png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
-      }
-
-      else if (png_ptr->screen_gamma != 0)
-         /* The converse - assume the file matches the screen, note that this
-          * perhaps undesireable default can (from 1.5.4) be changed by calling
-          * png_set_alpha_mode (even if the alpha handling mode isn't required
-          * or isn't changed from the default.)
-          */
-         png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);
-
-      else /* neither are set */
-         /* Just in case the following prevents any processing - file and screen
-          * are both assumed to be linear and there is no way to introduce a
-          * third gamma value other than png_set_background with 'UNIQUE', and,
-          * prior to 1.5.4
-          */
-         png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;
-
-      /* We have a gamma value now. */
-      png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
-
-      /* Now turn the gamma transformation on or off as appropriate.  Notice
-       * that PNG_GAMMA just refers to the file->screen correction.  Alpha
-       * composition may independently cause gamma correction because it needs
-       * linear data (e.g. if the file has a gAMA chunk but the screen gamma
-       * hasn't been specified.)  In any case this flag may get turned off in
-       * the code immediately below if the transform can be handled outside the
-       * row loop.
-       */
-      if (gamma_correction)
-         png_ptr->transformations |= PNG_GAMMA;
-
-      else
-         png_ptr->transformations &= ~PNG_GAMMA;
-   }
-#endif
-
-   /* Certain transformations have the effect of preventing other
-    * transformations that happen afterward in png_do_read_transformations,
-    * resolve the interdependencies here.  From the code of
-    * png_do_read_transformations the order is:
-    *
-    *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
-    *  2) PNG_STRIP_ALPHA (if no compose)
-    *  3) PNG_RGB_TO_GRAY
-    *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
-    *  5) PNG_COMPOSE
-    *  6) PNG_GAMMA
-    *  7) PNG_STRIP_ALPHA (if compose)
-    *  8) PNG_ENCODE_ALPHA
-    *  9) PNG_SCALE_16_TO_8
-    * 10) PNG_16_TO_8
-    * 11) PNG_QUANTIZE (converts to palette)
-    * 12) PNG_EXPAND_16
-    * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
-    * 14) PNG_INVERT_MONO
-    * 15) PNG_SHIFT
-    * 16) PNG_PACK
-    * 17) PNG_BGR
-    * 18) PNG_PACKSWAP
-    * 19) PNG_FILLER (includes PNG_ADD_ALPHA)
-    * 20) PNG_INVERT_ALPHA
-    * 21) PNG_SWAP_ALPHA
-    * 22) PNG_SWAP_BYTES
-    * 23) PNG_USER_TRANSFORM [must be last]
-    */
-#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
-   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
-      !(png_ptr->transformations & PNG_COMPOSE))
-   {
-      /* Stripping the alpha channel happens immediately after the 'expand'
-       * transformations, before all other transformation, so it cancels out
-       * the alpha handling.  It has the side effect negating the effect of
-       * PNG_EXPAND_tRNS too:
-       */
-      png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
-         PNG_EXPAND_tRNS);
-      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-
-      /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
-       * so transparency information would remain just so long as it wasn't
-       * expanded.  This produces unexpected API changes if the set of things
-       * that do PNG_EXPAND_tRNS changes (perfectly possible given the
-       * documentation - which says ask for what you want, accept what you
-       * get.)  This makes the behavior consistent from 1.5.4:
-       */
-      png_ptr->num_trans = 0;
-   }
-#endif /* STRIP_ALPHA supported, no COMPOSE */
-
-#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
-   /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
-    * settings will have no effect.
-    */
-   if (!png_gamma_significant(png_ptr->screen_gamma))
-   {
-      png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
-      png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
-   }
-#endif
-
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-   /* Make sure the coefficients for the rgb to gray conversion are set
-    * appropriately.
-    */
-   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
-      png_colorspace_set_rgb_coefficients(png_ptr);
-#endif
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
-   /* Detect gray background and attempt to enable optimization for
-    * gray --> RGB case.
-    *
-    * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
-    * RGB_ALPHA (in which case need_expand is superfluous anyway), the
-    * background color might actually be gray yet not be flagged as such.
-    * This is not a problem for the current code, which uses
-    * PNG_BACKGROUND_IS_GRAY only to decide when to do the
-    * png_do_gray_to_rgb() transformation.
-    *
-    * TODO: this code needs to be revised to avoid the complexity and
-    * interdependencies.  The color type of the background should be recorded in
-    * png_set_background, along with the bit depth, then the code has a record
-    * of exactly what color space the background is currently in.
-    */
-   if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
-   {
-      /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
-       * the file was grayscale the background value is gray.
-       */
-      if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
-         png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
-   }
-
-   else if (png_ptr->transformations & PNG_COMPOSE)
-   {
-      /* PNG_COMPOSE: png_set_background was called with need_expand false,
-       * so the color is in the color space of the output or png_set_alpha_mode
-       * was called and the color is black.  Ignore RGB_TO_GRAY because that
-       * happens before GRAY_TO_RGB.
-       */
-      if (png_ptr->transformations & PNG_GRAY_TO_RGB)
-      {
-         if (png_ptr->background.red == png_ptr->background.green &&
-             png_ptr->background.red == png_ptr->background.blue)
-         {
-            png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
-            png_ptr->background.gray = png_ptr->background.red;
-         }
-      }
-   }
-#endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
-#endif /* PNG_READ_GRAY_TO_RGB_SUPPORTED */
-
-   /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
-    * can be performed directly on the palette, and some (such as rgb to gray)
-    * can be optimized inside the palette.  This is particularly true of the
-    * composite (background and alpha) stuff, which can be pretty much all done
-    * in the palette even if the result is expanded to RGB or gray afterward.
-    *
-    * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
-    * earlier and the palette stuff is actually handled on the first row.  This
-    * leads to the reported bug that the palette returned by png_get_PLTE is not
-    * updated.
-    */
-   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-      png_init_palette_transformations(png_ptr);
-
-   else
-      png_init_rgb_transformations(png_ptr);
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
-   defined(PNG_READ_EXPAND_16_SUPPORTED)
-   if ((png_ptr->transformations & PNG_EXPAND_16) &&
-      (png_ptr->transformations & PNG_COMPOSE) &&
-      !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
-      png_ptr->bit_depth != 16)
-   {
-      /* TODO: fix this.  Because the expand_16 operation is after the compose
-       * handling the background color must be 8, not 16, bits deep, but the
-       * application will supply a 16-bit value so reduce it here.
-       *
-       * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
-       * present, so that case is ok (until do_expand_16 is moved.)
-       *
-       * NOTE: this discards the low 16 bits of the user supplied background
-       * color, but until expand_16 works properly there is no choice!
-       */
-#     define CHOP(x) (x)=((png_uint_16)PNG_DIV257(x))
-      CHOP(png_ptr->background.red);
-      CHOP(png_ptr->background.green);
-      CHOP(png_ptr->background.blue);
-      CHOP(png_ptr->background.gray);
-#     undef CHOP
-   }
-#endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
-   (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
-   defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
-   if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
-      (png_ptr->transformations & PNG_COMPOSE) &&
-      !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
-      png_ptr->bit_depth == 16)
-   {
-      /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
-       * component this will also happen after PNG_COMPOSE and so the background
-       * color must be pre-expanded here.
-       *
-       * TODO: fix this too.
-       */
-      png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
-      png_ptr->background.green =
-         (png_uint_16)(png_ptr->background.green * 257);
-      png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
-      png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
-   }
-#endif
-
-   /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
-    * background support (see the comments in scripts/pnglibconf.dfa), this
-    * allows pre-multiplication of the alpha channel to be implemented as
-    * compositing on black.  This is probably sub-optimal and has been done in
-    * 1.5.4 betas simply to enable external critique and testing (i.e. to
-    * implement the new API quickly, without lots of internal changes.)
-    */
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-#  ifdef PNG_READ_BACKGROUND_SUPPORTED
-      /* Includes ALPHA_MODE */
-      png_ptr->background_1 = png_ptr->background;
-#  endif
-
-   /* This needs to change - in the palette image case a whole set of tables are
-    * built when it would be quicker to just calculate the correct value for
-    * each palette entry directly.  Also, the test is too tricky - why check
-    * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
-    * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
-    * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
-    * the gamma tables will not be built even if composition is required on a
-    * gamma encoded value.
-    *
-    * In 1.5.4 this is addressed below by an additional check on the individual
-    * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
-    * tables.
-    */
-   if ((png_ptr->transformations & PNG_GAMMA)
-      || ((png_ptr->transformations & PNG_RGB_TO_GRAY)
-         && (png_gamma_significant(png_ptr->colorspace.gamma) ||
-            png_gamma_significant(png_ptr->screen_gamma)))
-      || ((png_ptr->transformations & PNG_COMPOSE)
-         && (png_gamma_significant(png_ptr->colorspace.gamma)
-            || png_gamma_significant(png_ptr->screen_gamma)
-#  ifdef PNG_READ_BACKGROUND_SUPPORTED
-            || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE
-               && png_gamma_significant(png_ptr->background_gamma))
-#  endif
-      )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA)
-         && png_gamma_significant(png_ptr->screen_gamma))
-      )
-   {
-      png_build_gamma_table(png_ptr, png_ptr->bit_depth);
-
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-      if (png_ptr->transformations & PNG_COMPOSE)
-      {
-         /* Issue a warning about this combination: because RGB_TO_GRAY is
-          * optimized to do the gamma transform if present yet do_background has
-          * to do the same thing if both options are set a
-          * double-gamma-correction happens.  This is true in all versions of
-          * libpng to date.
-          */
-         if (png_ptr->transformations & PNG_RGB_TO_GRAY)
-            png_warning(png_ptr,
-               "libpng does not support gamma+background+rgb_to_gray");
-
-         if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-         {
-            /* We don't get to here unless there is a tRNS chunk with non-opaque
-             * entries - see the checking code at the start of this function.
-             */
-            png_color back, back_1;
-            png_colorp palette = png_ptr->palette;
-            int num_palette = png_ptr->num_palette;
-            int i;
-            if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
-            {
-
-               back.red = png_ptr->gamma_table[png_ptr->background.red];
-               back.green = png_ptr->gamma_table[png_ptr->background.green];
-               back.blue = png_ptr->gamma_table[png_ptr->background.blue];
-
-               back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
-               back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
-               back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
-            }
-            else
-            {
-               png_fixed_point g, gs;
-
-               switch (png_ptr->background_gamma_type)
-               {
-                  case PNG_BACKGROUND_GAMMA_SCREEN:
-                     g = (png_ptr->screen_gamma);
-                     gs = PNG_FP_1;
-                     break;
-
-                  case PNG_BACKGROUND_GAMMA_FILE:
-                     g = png_reciprocal(png_ptr->colorspace.gamma);
-                     gs = png_reciprocal2(png_ptr->colorspace.gamma,
-                        png_ptr->screen_gamma);
-                     break;
-
-                  case PNG_BACKGROUND_GAMMA_UNIQUE:
-                     g = png_reciprocal(png_ptr->background_gamma);
-                     gs = png_reciprocal2(png_ptr->background_gamma,
-                        png_ptr->screen_gamma);
-                     break;
-                  default:
-                     g = PNG_FP_1;    /* back_1 */
-                     gs = PNG_FP_1;   /* back */
-                     break;
-               }
-
-               if (png_gamma_significant(gs))
-               {
-                  back.red = png_gamma_8bit_correct(png_ptr->background.red,
-                      gs);
-                  back.green = png_gamma_8bit_correct(png_ptr->background.green,
-                      gs);
-                  back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
-                      gs);
-               }
-
-               else
-               {
-                  back.red   = (png_byte)png_ptr->background.red;
-                  back.green = (png_byte)png_ptr->background.green;
-                  back.blue  = (png_byte)png_ptr->background.blue;
-               }
-
-               if (png_gamma_significant(g))
-               {
-                  back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
-                     g);
-                  back_1.green = png_gamma_8bit_correct(
-                     png_ptr->background.green, g);
-                  back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
-                     g);
-               }
-
-               else
-               {
-                  back_1.red   = (png_byte)png_ptr->background.red;
-                  back_1.green = (png_byte)png_ptr->background.green;
-                  back_1.blue  = (png_byte)png_ptr->background.blue;
-               }
-            }
-
-            for (i = 0; i < num_palette; i++)
-            {
-               if (i < (int)png_ptr->num_trans &&
-                   png_ptr->trans_alpha[i] != 0xff)
-               {
-                  if (png_ptr->trans_alpha[i] == 0)
-                  {
-                     palette[i] = back;
-                  }
-                  else /* if (png_ptr->trans_alpha[i] != 0xff) */
-                  {
-                     png_byte v, w;
-
-                     v = png_ptr->gamma_to_1[palette[i].red];
-                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
-                     palette[i].red = png_ptr->gamma_from_1[w];
-
-                     v = png_ptr->gamma_to_1[palette[i].green];
-                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
-                     palette[i].green = png_ptr->gamma_from_1[w];
-
-                     v = png_ptr->gamma_to_1[palette[i].blue];
-                     png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
-                     palette[i].blue = png_ptr->gamma_from_1[w];
-                  }
-               }
-               else
-               {
-                  palette[i].red = png_ptr->gamma_table[palette[i].red];
-                  palette[i].green = png_ptr->gamma_table[palette[i].green];
-                  palette[i].blue = png_ptr->gamma_table[palette[i].blue];
-               }
-            }
-
-            /* Prevent the transformations being done again.
-             *
-             * NOTE: this is highly dubious; it removes the transformations in
-             * place.  This seems inconsistent with the general treatment of the
-             * transformations elsewhere.
-             */
-            png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
-         } /* color_type == PNG_COLOR_TYPE_PALETTE */
-
-         /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
-         else /* color_type != PNG_COLOR_TYPE_PALETTE */
-         {
-            int gs_sig, g_sig;
-            png_fixed_point g = PNG_FP_1;  /* Correction to linear */
-            png_fixed_point gs = PNG_FP_1; /* Correction to screen */
-
-            switch (png_ptr->background_gamma_type)
-            {
-               case PNG_BACKGROUND_GAMMA_SCREEN:
-                  g = png_ptr->screen_gamma;
-                  /* gs = PNG_FP_1; */
-                  break;
-
-               case PNG_BACKGROUND_GAMMA_FILE:
-                  g = png_reciprocal(png_ptr->colorspace.gamma);
-                  gs = png_reciprocal2(png_ptr->colorspace.gamma,
-                     png_ptr->screen_gamma);
-                  break;
-
-               case PNG_BACKGROUND_GAMMA_UNIQUE:
-                  g = png_reciprocal(png_ptr->background_gamma);
-                  gs = png_reciprocal2(png_ptr->background_gamma,
-                      png_ptr->screen_gamma);
-                  break;
-
-               default:
-                  png_error(png_ptr, "invalid background gamma type");
-            }
-
-            g_sig = png_gamma_significant(g);
-            gs_sig = png_gamma_significant(gs);
-
-            if (g_sig)
-               png_ptr->background_1.gray = png_gamma_correct(png_ptr,
-                   png_ptr->background.gray, g);
-
-            if (gs_sig)
-               png_ptr->background.gray = png_gamma_correct(png_ptr,
-                   png_ptr->background.gray, gs);
-
-            if ((png_ptr->background.red != png_ptr->background.green) ||
-                (png_ptr->background.red != png_ptr->background.blue) ||
-                (png_ptr->background.red != png_ptr->background.gray))
-            {
-               /* RGB or RGBA with color background */
-               if (g_sig)
-               {
-                  png_ptr->background_1.red = png_gamma_correct(png_ptr,
-                      png_ptr->background.red, g);
-
-                  png_ptr->background_1.green = png_gamma_correct(png_ptr,
-                      png_ptr->background.green, g);
-
-                  png_ptr->background_1.blue = png_gamma_correct(png_ptr,
-                      png_ptr->background.blue, g);
-               }
-
-               if (gs_sig)
-               {
-                  png_ptr->background.red = png_gamma_correct(png_ptr,
-                      png_ptr->background.red, gs);
-
-                  png_ptr->background.green = png_gamma_correct(png_ptr,
-                      png_ptr->background.green, gs);
-
-                  png_ptr->background.blue = png_gamma_correct(png_ptr,
-                      png_ptr->background.blue, gs);
-               }
-            }
-
-            else
-            {
-               /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
-               png_ptr->background_1.red = png_ptr->background_1.green
-                   = png_ptr->background_1.blue = png_ptr->background_1.gray;
-
-               png_ptr->background.red = png_ptr->background.green
-                   = png_ptr->background.blue = png_ptr->background.gray;
-            }
-
-            /* The background is now in screen gamma: */
-            png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
-         } /* color_type != PNG_COLOR_TYPE_PALETTE */
-      }/* png_ptr->transformations & PNG_BACKGROUND */
-
-      else
-      /* Transformation does not include PNG_BACKGROUND */
-#endif /* PNG_READ_BACKGROUND_SUPPORTED */
-      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-         /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
-         && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
-         (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
-#endif
-         )
-      {
-         png_colorp palette = png_ptr->palette;
-         int num_palette = png_ptr->num_palette;
-         int i;
-
-         /* NOTE: there are other transformations that should probably be in
-          * here too.
-          */
-         for (i = 0; i < num_palette; i++)
-         {
-            palette[i].red = png_ptr->gamma_table[palette[i].red];
-            palette[i].green = png_ptr->gamma_table[palette[i].green];
-            palette[i].blue = png_ptr->gamma_table[palette[i].blue];
-         }
-
-         /* Done the gamma correction. */
-         png_ptr->transformations &= ~PNG_GAMMA;
-      } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
-   }
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-   else
-#endif
-#endif /* PNG_READ_GAMMA_SUPPORTED */
-
-#ifdef PNG_READ_BACKGROUND_SUPPORTED
-   /* No GAMMA transformation (see the hanging else 4 lines above) */
-   if ((png_ptr->transformations & PNG_COMPOSE) &&
-       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
-   {
-      int i;
-      int istop = (int)png_ptr->num_trans;
-      png_color back;
-      png_colorp palette = png_ptr->palette;
-
-      back.red   = (png_byte)png_ptr->background.red;
-      back.green = (png_byte)png_ptr->background.green;
-      back.blue  = (png_byte)png_ptr->background.blue;
-
-      for (i = 0; i < istop; i++)
-      {
-         if (png_ptr->trans_alpha[i] == 0)
-         {
-            palette[i] = back;
-         }
-
-         else if (png_ptr->trans_alpha[i] != 0xff)
-         {
-            /* The png_composite() macro is defined in png.h */
-            png_composite(palette[i].red, palette[i].red,
-                png_ptr->trans_alpha[i], back.red);
-
-            png_composite(palette[i].green, palette[i].green,
-                png_ptr->trans_alpha[i], back.green);
-
-            png_composite(palette[i].blue, palette[i].blue,
-                png_ptr->trans_alpha[i], back.blue);
-         }
-      }
-
-      png_ptr->transformations &= ~PNG_COMPOSE;
-          
-          //png_ptr->flags |= PNG_FLAG_STRIP_ALPHA; /* Add by Sunliang.Liu */
-   }
-#endif /* PNG_READ_BACKGROUND_SUPPORTED */
-
-#ifdef PNG_READ_SHIFT_SUPPORTED
-   if ((png_ptr->transformations & PNG_SHIFT) &&
-      !(png_ptr->transformations & PNG_EXPAND) &&
-       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
-   {
-      int i;
-      int istop = png_ptr->num_palette;
-      int shift = 8 - png_ptr->sig_bit.red;
-
-      png_ptr->transformations &= ~PNG_SHIFT;
-
-      /* significant bits can be in the range 1 to 7 for a meaninful result, if
-       * the number of significant bits is 0 then no shift is done (this is an
-       * error condition which is silently ignored.)
-       */
-      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
-      {
-         int component = png_ptr->palette[i].red;
-
-         component >>= shift;
-         png_ptr->palette[i].red = (png_byte)component;
-      }
-
-      shift = 8 - png_ptr->sig_bit.green;
-      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
-      {
-         int component = png_ptr->palette[i].green;
-
-         component >>= shift;
-         png_ptr->palette[i].green = (png_byte)component;
-      }
-
-      shift = 8 - png_ptr->sig_bit.blue;
-      if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
-      {
-         int component = png_ptr->palette[i].blue;
-
-         component >>= shift;
-         png_ptr->palette[i].blue = (png_byte)component;
-      }
-   }
-#endif  /* PNG_READ_SHIFT_SUPPORTED */
-}
-
-/* Modify the info structure to reflect the transformations.  The
- * info should be updated so a PNG file could be written with it,
- * assuming the transformations result in valid PNG data.
- */
-void /* PRIVATE */
-png_read_transform_info(png_structrp png_ptr, png_inforp info_ptr)
-{
-   png_debug(1, "in png_read_transform_info");
-
-#ifdef PNG_READ_EXPAND_SUPPORTED
-   if (png_ptr->transformations & PNG_EXPAND)
-   {
-      if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         /* This check must match what actually happens in
-          * png_do_expand_palette; if it ever checks the tRNS chunk to see if
-          * it is all opaque we must do the same (at present it does not.)
-          */
-         if (png_ptr->num_trans > 0)
-            info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
-
-         else
-            info_ptr->color_type = PNG_COLOR_TYPE_RGB;
-
-         info_ptr->bit_depth = 8;
-         info_ptr->num_trans = 0;
-      }
-      else
-      {
-         if (png_ptr->num_trans)
-         {
-            if (png_ptr->transformations & PNG_EXPAND_tRNS)
-               info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
-         }
-         if (info_ptr->bit_depth < 8)
-            info_ptr->bit_depth = 8;
-
-         info_ptr->num_trans = 0;
-      }
-   }
-#endif
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
-   defined(PNG_READ_ALPHA_MODE_SUPPORTED)
-   /* The following is almost certainly wrong unless the background value is in
-    * the screen space!
-    */
-   if (png_ptr->transformations & PNG_COMPOSE)
-      info_ptr->background = png_ptr->background;
-#endif
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
-    * however it seems that the code in png_init_read_transformations, which has
-    * been called before this from png_read_update_info->png_read_start_row
-    * sometimes does the gamma transform and cancels the flag.
-    *
-    * TODO: this looks wrong; the info_ptr should end up with a gamma equal to
-    * the screen_gamma value.  The following probably results in weirdness if
-    * the info_ptr is used by the app after the rows have been read.
-    */
-   info_ptr->colorspace.gamma = png_ptr->colorspace.gamma;
-#endif
-
-   if (info_ptr->bit_depth == 16)
-   {
-#  ifdef PNG_READ_16BIT_SUPPORTED
-#     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
-         if (png_ptr->transformations & PNG_SCALE_16_TO_8)
-            info_ptr->bit_depth = 8;
-#     endif
-
-#     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
-         if (png_ptr->transformations & PNG_16_TO_8)
-            info_ptr->bit_depth = 8;
-#     endif
-
-#  else
-      /* No 16 bit support: force chopping 16-bit input down to 8, in this case
-       * the app program can chose if both APIs are available by setting the
-       * correct scaling to use.
-       */
-#     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
-         /* For compatibility with previous versions use the strip method by
-          * default.  This code works because if PNG_SCALE_16_TO_8 is already
-          * set the code below will do that in preference to the chop.
-          */
-         png_ptr->transformations |= PNG_16_TO_8;
-         info_ptr->bit_depth = 8;
-#     else
-
-#        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
-            png_ptr->transformations |= PNG_SCALE_16_TO_8;
-            info_ptr->bit_depth = 8;
-#        else
-
-            CONFIGURATION ERROR: you must enable at least one 16 to 8 method
-#        endif
-#    endif
-#endif /* !READ_16BIT_SUPPORTED */
-   }
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
-      info_ptr->color_type = (png_byte)(info_ptr->color_type |
-         PNG_COLOR_MASK_COLOR);
-#endif
-
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
-      info_ptr->color_type = (png_byte)(info_ptr->color_type &
-         ~PNG_COLOR_MASK_COLOR);
-#endif
-
-#ifdef PNG_READ_QUANTIZE_SUPPORTED
-   if (png_ptr->transformations & PNG_QUANTIZE)
-   {
-      if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
-          (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
-          png_ptr->palette_lookup && info_ptr->bit_depth == 8)
-      {
-         info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
-      }
-   }
-#endif
-
-#ifdef PNG_READ_EXPAND_16_SUPPORTED
-   if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
-      info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
-   {
-      info_ptr->bit_depth = 16;
-   }
-#endif
-
-#ifdef PNG_READ_PACK_SUPPORTED
-   if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
-      info_ptr->bit_depth = 8;
-#endif
-
-   if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
-      info_ptr->channels = 1;
-
-   else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
-      info_ptr->channels = 3;
-
-   else
-      info_ptr->channels = 1;
-
-#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
-   if (png_ptr->transformations & PNG_STRIP_ALPHA)
-   {
-      info_ptr->color_type = (png_byte)(info_ptr->color_type &
-         ~PNG_COLOR_MASK_ALPHA);
-      info_ptr->num_trans = 0;
-   }
-#endif
-
-   if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
-      info_ptr->channels++;
-
-#ifdef PNG_READ_FILLER_SUPPORTED
-   /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
-   if ((png_ptr->transformations & PNG_FILLER) &&
-       ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
-       (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
-   {
-      info_ptr->channels++;
-      /* If adding a true alpha channel not just filler */
-      if (png_ptr->transformations & PNG_ADD_ALPHA)
-         info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
-   }
-#endif
-
-#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
-defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
-   if (png_ptr->transformations & PNG_USER_TRANSFORM)
-   {
-      if (info_ptr->bit_depth < png_ptr->user_transform_depth)
-         info_ptr->bit_depth = png_ptr->user_transform_depth;
-
-      if (info_ptr->channels < png_ptr->user_transform_channels)
-         info_ptr->channels = png_ptr->user_transform_channels;
-   }
-#endif
-
-   info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
-       info_ptr->bit_depth);
-
-   info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
-
-   /* Adding in 1.5.4: cache the above value in png_struct so that we can later
-    * check in png_rowbytes that the user buffer won't get overwritten.  Note
-    * that the field is not always set - if png_read_update_info isn't called
-    * the application has to either not do any transforms or get the calculation
-    * right itself.
-    */
-   png_ptr->info_rowbytes = info_ptr->rowbytes;
-
-#ifndef PNG_READ_EXPAND_SUPPORTED
-   if (png_ptr)
-      return;
-#endif
-}
-
-/* Transform the row.  The order of transformations is significant,
- * and is very touchy.  If you add a transformation, take care to
- * decide how it fits in with the other transformations here.
- */
-void /* PRIVATE */
-png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
-{
-   png_debug(1, "in png_do_read_transformations");
-
-   if (png_ptr->row_buf == NULL)
-   {
-      /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
-       * error is incredibly rare and incredibly easy to debug without this
-       * information.
-       */
-      png_error(png_ptr, "NULL row buffer");
-   }
-
-   /* The following is debugging; prior to 1.5.4 the code was never compiled in;
-    * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
-    * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.6 the new flag is set only for
-    * all transformations, however in practice the ROW_INIT always gets done on
-    * demand, if necessary.
-    */
-   if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
-      !(png_ptr->flags & PNG_FLAG_ROW_INIT))
-   {
-      /* Application has failed to call either png_read_start_image() or
-       * png_read_update_info() after setting transforms that expand pixels.
-       * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
-       */
-      png_error(png_ptr, "Uninitialized row");
-   }
-
-#ifdef PNG_READ_EXPAND_SUPPORTED
-   if (png_ptr->transformations & PNG_EXPAND)
-   {
-      if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
-      {
-         png_do_expand_palette(row_info, png_ptr->row_buf + 1,
-             png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
-      }
-
-      else
-      {
-         if (png_ptr->num_trans &&
-             (png_ptr->transformations & PNG_EXPAND_tRNS))
-            png_do_expand(row_info, png_ptr->row_buf + 1,
-                &(png_ptr->trans_color));
-
-         else
-            png_do_expand(row_info, png_ptr->row_buf + 1,
-                NULL);
-      }
-   }
-#endif
-
-#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
-   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
-      !(png_ptr->transformations & PNG_COMPOSE) &&
-      (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
-      row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
-      png_do_strip_channel(row_info, png_ptr->row_buf + 1,
-         0 /* at_start == false, because SWAP_ALPHA happens later */);
-#endif
-
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
-   {
-      int rgb_error =
-          png_do_rgb_to_gray(png_ptr, row_info,
-              png_ptr->row_buf + 1);
-
-      if (rgb_error)
-      {
-         png_ptr->rgb_to_gray_status=1;
-         if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
-             PNG_RGB_TO_GRAY_WARN)
-            png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
-
-         if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
-             PNG_RGB_TO_GRAY_ERR)
-            png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
-      }
-   }
-#endif
-
-/* From Andreas Dilger e-mail to png-implement, 26 March 1998:
- *
- *   In most cases, the "simple transparency" should be done prior to doing
- *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
- *   pixel is transparent.  You would also need to make sure that the
- *   transparency information is upgraded to RGB.
- *
- *   To summarize, the current flow is:
- *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
- *                                   with background "in place" if transparent,
- *                                   convert to RGB if necessary
- *   - Gray + alpha -> composite with gray background and remove alpha bytes,
- *                                   convert to RGB if necessary
- *
- *   To support RGB backgrounds for gray images we need:
- *   - Gray + simple transparency -> convert to RGB + simple transparency,
- *                                   compare 3 or 6 bytes and composite with
- *                                   background "in place" if transparent
- *                                   (3x compare/pixel compared to doing
- *                                   composite with gray bkgrnd)
- *   - Gray + alpha -> convert to RGB + alpha, composite with background and
- *                                   remove alpha bytes (3x float
- *                                   operations/pixel compared with composite
- *                                   on gray background)
- *
- *  Greg's change will do this.  The reason it wasn't done before is for
- *  performance, as this increases the per-pixel operations.  If we would check
- *  in advance if the background was gray or RGB, and position the gray-to-RGB
- *  transform appropriately, then it would save a lot of work/time.
- */
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-   /* If gray -> RGB, do so now only if background is non-gray; else do later
-    * for performance reasons
-    */
-   if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
-       !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
-      png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
-#endif
-
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
-   defined(PNG_READ_ALPHA_MODE_SUPPORTED)
-   if (png_ptr->transformations & PNG_COMPOSE)
-      png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
-#endif
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   if ((png_ptr->transformations & PNG_GAMMA) &&
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-      /* Because RGB_TO_GRAY does the gamma transform. */
-      !(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
-#endif
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
-   defined(PNG_READ_ALPHA_MODE_SUPPORTED)
-      /* Because PNG_COMPOSE does the gamma transform if there is something to
-       * do (if there is an alpha channel or transparency.)
-       */
-       !((png_ptr->transformations & PNG_COMPOSE) &&
-       ((png_ptr->num_trans != 0) ||
-       (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
-#endif
-      /* Because png_init_read_transformations transforms the palette, unless
-       * RGB_TO_GRAY will do the transform.
-       */
-       (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
-      png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
-#endif
-
-#ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
-   if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
-      (png_ptr->transformations & PNG_COMPOSE) &&
-      (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
-      row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
-      png_do_strip_channel(row_info, png_ptr->row_buf + 1,
-         0 /* at_start == false, because SWAP_ALPHA happens later */);
-#endif
-
-#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
-   if ((png_ptr->transformations & PNG_ENCODE_ALPHA) &&
-      (row_info->color_type & PNG_COLOR_MASK_ALPHA))
-      png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
-#endif
-
-#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
-   if (png_ptr->transformations & PNG_SCALE_16_TO_8)
-      png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
-   /* There is no harm in doing both of these because only one has any effect,
-    * by putting the 'scale' option first if the app asks for scale (either by
-    * calling the API or in a TRANSFORM flag) this is what happens.
-    */
-   if (png_ptr->transformations & PNG_16_TO_8)
-      png_do_chop(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_QUANTIZE_SUPPORTED
-   if (png_ptr->transformations & PNG_QUANTIZE)
-   {
-      png_do_quantize(row_info, png_ptr->row_buf + 1,
-          png_ptr->palette_lookup, png_ptr->quantize_index);
-
-      if (row_info->rowbytes == 0)
-         png_error(png_ptr, "png_do_quantize returned rowbytes=0");
-   }
-#endif /* PNG_READ_QUANTIZE_SUPPORTED */
-
-#ifdef PNG_READ_EXPAND_16_SUPPORTED
-   /* Do the expansion now, after all the arithmetic has been done.  Notice
-    * that previous transformations can handle the PNG_EXPAND_16 flag if this
-    * is efficient (particularly true in the case of gamma correction, where
-    * better accuracy results faster!)
-    */
-   if (png_ptr->transformations & PNG_EXPAND_16)
-      png_do_expand_16(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-   /* NOTE: moved here in 1.5.4 (from much later in this list.) */
-   if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
-       (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
-      png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_INVERT_SUPPORTED
-   if (png_ptr->transformations & PNG_INVERT_MONO)
-      png_do_invert(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_SHIFT_SUPPORTED
-   if (png_ptr->transformations & PNG_SHIFT)
-      png_do_unshift(row_info, png_ptr->row_buf + 1,
-          &(png_ptr->shift));
-#endif
-
-#ifdef PNG_READ_PACK_SUPPORTED
-   if (png_ptr->transformations & PNG_PACK)
-      png_do_unpack(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
-   /* Added at libpng-1.5.10 */
-   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
-       png_ptr->num_palette_max >= 0)
-      png_do_check_palette_indexes(png_ptr, row_info);
-#endif
-
-#ifdef PNG_READ_BGR_SUPPORTED
-   if (png_ptr->transformations & PNG_BGR)
-      png_do_bgr(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_PACKSWAP_SUPPORTED
-   if (png_ptr->transformations & PNG_PACKSWAP)
-      png_do_packswap(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_FILLER_SUPPORTED
-   if (png_ptr->transformations & PNG_FILLER)
-      png_do_read_filler(row_info, png_ptr->row_buf + 1,
-          (png_uint_32)png_ptr->filler, png_ptr->flags);
-#endif
-
-#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
-   if (png_ptr->transformations & PNG_INVERT_ALPHA)
-      png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
-   if (png_ptr->transformations & PNG_SWAP_ALPHA)
-      png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
-#endif
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-#ifdef PNG_READ_SWAP_SUPPORTED
-   if (png_ptr->transformations & PNG_SWAP_BYTES)
-      png_do_swap(row_info, png_ptr->row_buf + 1);
-#endif
-#endif
-
-#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
-   if (png_ptr->transformations & PNG_USER_TRANSFORM)
-    {
-      if (png_ptr->read_user_transform_fn != NULL)
-         (*(png_ptr->read_user_transform_fn)) /* User read transform function */
-             (png_ptr,     /* png_ptr */
-             row_info,     /* row_info: */
-                /*  png_uint_32 width;       width of row */
-                /*  png_size_t rowbytes;     number of bytes in row */
-                /*  png_byte color_type;     color type of pixels */
-                /*  png_byte bit_depth;      bit depth of samples */
-                /*  png_byte channels;       number of channels (1-4) */
-                /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
-             png_ptr->row_buf + 1);    /* start of pixel data for row */
-#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
-      if (png_ptr->user_transform_depth)
-         row_info->bit_depth = png_ptr->user_transform_depth;
-
-      if (png_ptr->user_transform_channels)
-         row_info->channels = png_ptr->user_transform_channels;
-#endif
-      row_info->pixel_depth = (png_byte)(row_info->bit_depth *
-          row_info->channels);
-
-      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
-   }
-#endif
-}
-
-#ifdef PNG_READ_PACK_SUPPORTED
-/* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
- * without changing the actual values.  Thus, if you had a row with
- * a bit depth of 1, you would end up with bytes that only contained
- * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
- * png_do_shift() after this.
- */
-void /* PRIVATE */
-png_do_unpack(png_row_infop row_info, png_bytep row)
-{
-   png_debug(1, "in png_do_unpack");
-
-   if (row_info->bit_depth < 8)
-   {
-      png_uint_32 i;
-      png_uint_32 row_width=row_info->width;
-
-      switch (row_info->bit_depth)
-      {
-         case 1:
-         {
-            png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
-            png_bytep dp = row + (png_size_t)row_width - 1;
-            png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
-            for (i = 0; i < row_width; i++)
-            {
-               *dp = (png_byte)((*sp >> shift) & 0x01);
-
-               if (shift == 7)
-               {
-                  shift = 0;
-                  sp--;
-               }
-
-               else
-                  shift++;
-
-               dp--;
-            }
-            break;
-         }
-
-         case 2:
-         {
-
-            png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
-            png_bytep dp = row + (png_size_t)row_width - 1;
-            png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
-            for (i = 0; i < row_width; i++)
-            {
-               *dp = (png_byte)((*sp >> shift) & 0x03);
-
-               if (shift == 6)
-               {
-                  shift = 0;
-                  sp--;
-               }
-
-               else
-                  shift += 2;
-
-               dp--;
-            }
-            break;
-         }
-
-         case 4:
-         {
-            png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
-            png_bytep dp = row + (png_size_t)row_width - 1;
-            png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
-            for (i = 0; i < row_width; i++)
-            {
-               *dp = (png_byte)((*sp >> shift) & 0x0f);
-
-               if (shift == 4)
-               {
-                  shift = 0;
-                  sp--;
-               }
-
-               else
-                  shift = 4;
-
-               dp--;
-            }
-            break;
-         }
-
-         default:
-            break;
-      }
-      row_info->bit_depth = 8;
-      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
-      row_info->rowbytes = row_width * row_info->channels;
-   }
-}
-#endif
-
-#ifdef PNG_READ_SHIFT_SUPPORTED
-/* Reverse the effects of png_do_shift.  This routine merely shifts the
- * pixels back to their significant bits values.  Thus, if you have
- * a row of bit depth 8, but only 5 are significant, this will shift
- * the values back to 0 through 31.
- */
-void /* PRIVATE */
-png_do_unshift(png_row_infop row_info, png_bytep row,
-    png_const_color_8p sig_bits)
-{
-   int color_type;
-
-   png_debug(1, "in png_do_unshift");
-
-   /* The palette case has already been handled in the _init routine. */
-   color_type = row_info->color_type;
-
-   if (color_type != PNG_COLOR_TYPE_PALETTE)
-   {
-      int shift[4];
-      int channels = 0;
-      int bit_depth = row_info->bit_depth;
-
-      if (color_type & PNG_COLOR_MASK_COLOR)
-      {
-         shift[channels++] = bit_depth - sig_bits->red;
-         shift[channels++] = bit_depth - sig_bits->green;
-         shift[channels++] = bit_depth - sig_bits->blue;
-      }
-
-      else
-      {
-         shift[channels++] = bit_depth - sig_bits->gray;
-      }
-
-      if (color_type & PNG_COLOR_MASK_ALPHA)
-      {
-         shift[channels++] = bit_depth - sig_bits->alpha;
-      }
-
-      {
-         int c, have_shift;
-
-         for (c = have_shift = 0; c < channels; ++c)
-         {
-            /* A shift of more than the bit depth is an error condition but it
-             * gets ignored here.
-             */
-            if (shift[c] <= 0 || shift[c] >= bit_depth)
-               shift[c] = 0;
-
-            else
-               have_shift = 1;
-         }
-
-         if (!have_shift)
-            return;
-      }
-
-      switch (bit_depth)
-      {
-         default:
-         /* Must be 1bpp gray: should not be here! */
-            /* NOTREACHED */
-            break;
-
-         case 2:
-         /* Must be 2bpp gray */
-         /* assert(channels == 1 && shift[0] == 1) */
-         {
-            png_bytep bp = row;
-            png_bytep bp_end = bp + row_info->rowbytes;
-
-            while (bp < bp_end)
-            {
-               int b = (*bp >> 1) & 0x55;
-               *bp++ = (png_byte)b;
-            }
-            break;
-         }
-
-         case 4:
-         /* Must be 4bpp gray */
-         /* assert(channels == 1) */
-         {
-            png_bytep bp = row;
-            png_bytep bp_end = bp + row_info->rowbytes;
-            int gray_shift = shift[0];
-            int mask =  0xf >> gray_shift;
-
-            mask |= mask << 4;
-
-            while (bp < bp_end)
-            {
-               int b = (*bp >> gray_shift) & mask;
-               *bp++ = (png_byte)b;
-            }
-            break;
-         }
-
-         case 8:
-         /* Single byte components, G, GA, RGB, RGBA */
-         {
-            png_bytep bp = row;
-            png_bytep bp_end = bp + row_info->rowbytes;
-            int channel = 0;
-
-            while (bp < bp_end)
-            {
-               int b = *bp >> shift[channel];
-               if (++channel >= channels)
-                  channel = 0;
-               *bp++ = (png_byte)b;
-            }
-            break;
-         }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-         case 16:
-         /* Double byte components, G, GA, RGB, RGBA */
-         {
-            png_bytep bp = row;
-            png_bytep bp_end = bp + row_info->rowbytes;
-            int channel = 0;
-
-            while (bp < bp_end)
-            {
-               int value = (bp[0] << 8) + bp[1];
-
-               value >>= shift[channel];
-               if (++channel >= channels)
-                  channel = 0;
-               *bp++ = (png_byte)(value >> 8);
-               *bp++ = (png_byte)(value & 0xff);
-            }
-            break;
-         }
-#endif
-      }
-   }
-}
-#endif
-
-#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
-/* Scale rows of bit depth 16 down to 8 accurately */
-void /* PRIVATE */
-png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
-{
-   png_debug(1, "in png_do_scale_16_to_8");
-
-   if (row_info->bit_depth == 16)
-   {
-      png_bytep sp = row; /* source */
-      png_bytep dp = row; /* destination */
-      png_bytep ep = sp + row_info->rowbytes; /* end+1 */
-
-      while (sp < ep)
-      {
-         /* The input is an array of 16 bit components, these must be scaled to
-          * 8 bits each.  For a 16 bit value V the required value (from the PNG
-          * specification) is:
-          *
-          *    (V * 255) / 65535
-          *
-          * This reduces to round(V / 257), or floor((V + 128.5)/257)
-          *
-          * Represent V as the two byte value vhi.vlo.  Make a guess that the
-          * result is the top byte of V, vhi, then the correction to this value
-          * is:
-          *
-          *    error = floor(((V-vhi.vhi) + 128.5) / 257)
-          *          = floor(((vlo-vhi) + 128.5) / 257)
-          *
-          * This can be approximated using integer arithmetic (and a signed
-          * shift):
-          *
-          *    error = (vlo-vhi+128) >> 8;
-          *
-          * The approximate differs from the exact answer only when (vlo-vhi) is
-          * 128; it then gives a correction of +1 when the exact correction is
-          * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
-          * input values) is:
-          *
-          *    error = (vlo-vhi+128)*65535 >> 24;
-          *
-          * An alternative arithmetic calculation which also gives no errors is:
-          *
-          *    (V * 255 + 32895) >> 16
-          */
-
-         png_int_32 tmp = *sp++; /* must be signed! */
-         tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
-         *dp++ = (png_byte)tmp;
-      }
-
-      row_info->bit_depth = 8;
-      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
-      row_info->rowbytes = row_info->width * row_info->channels;
-   }
-}
-#endif
-
-#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
-void /* PRIVATE */
-/* Simply discard the low byte.  This was the default behavior prior
- * to libpng-1.5.4.
- */
-png_do_chop(png_row_infop row_info, png_bytep row)
-{
-   png_debug(1, "in png_do_chop");
-
-   if (row_info->bit_depth == 16)
-   {
-      png_bytep sp = row; /* source */
-      png_bytep dp = row; /* destination */
-      png_bytep ep = sp + row_info->rowbytes; /* end+1 */
-
-      while (sp < ep)
-      {
-         *dp++ = *sp;
-         sp += 2; /* skip low byte */
-      }
-
-      row_info->bit_depth = 8;
-      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
-      row_info->rowbytes = row_info->width * row_info->channels;
-   }
-}
-#endif
-
-#ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
-void /* PRIVATE */
-png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
-{
-   png_debug(1, "in png_do_read_swap_alpha");
-
-   {
-      png_uint_32 row_width = row_info->width;
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
-      {
-         /* This converts from RGBA to ARGB */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_byte save;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               save = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = save;
-            }
-         }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-         /* This converts from RRGGBBAA to AARRGGBB */
-         else
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_byte save[2];
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               save[0] = *(--sp);
-               save[1] = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = save[0];
-               *(--dp) = save[1];
-            }
-         }
-#endif
-      }
-
-      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
-      {
-         /* This converts from GA to AG */
-         if (row_info->bit_depth == 8)
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_byte save;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               save = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = save;
-            }
-         }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-         /* This converts from GGAA to AAGG */
-         else
-         {
-            png_bytep sp = row + row_info->rowbytes;
-            png_bytep dp = sp;
-            png_byte save[2];
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               save[0] = *(--sp);
-               save[1] = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = save[0];
-               *(--dp) = save[1];
-            }
-         }
-#endif
-      }
-   }
-}
-#endif
-
-#ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
-void /* PRIVATE */
-png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
-{
-   png_uint_32 row_width;
-   png_debug(1, "in png_do_read_invert_alpha");
-
-   row_width = row_info->width;
-   if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
-   {
-      if (row_info->bit_depth == 8)
-      {
-         /* This inverts the alpha channel in RGBA */
-         png_bytep sp = row + row_info->rowbytes;
-         png_bytep dp = sp;
-         png_uint_32 i;
-
-         for (i = 0; i < row_width; i++)
-         {
-            *(--dp) = (png_byte)(255 - *(--sp));
-
-/*          This does nothing:
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            We can replace it with:
-*/
-            sp-=3;
-            dp=sp;
-         }
-      }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-      /* This inverts the alpha channel in RRGGBBAA */
-      else
-      {
-         png_bytep sp = row + row_info->rowbytes;
-         png_bytep dp = sp;
-         png_uint_32 i;
-
-         for (i = 0; i < row_width; i++)
-         {
-            *(--dp) = (png_byte)(255 - *(--sp));
-            *(--dp) = (png_byte)(255 - *(--sp));
-
-/*          This does nothing:
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-            We can replace it with:
-*/
-            sp-=6;
-            dp=sp;
-         }
-      }
-#endif
-   }
-   else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
-   {
-      if (row_info->bit_depth == 8)
-      {
-         /* This inverts the alpha channel in GA */
-         png_bytep sp = row + row_info->rowbytes;
-         png_bytep dp = sp;
-         png_uint_32 i;
-
-         for (i = 0; i < row_width; i++)
-         {
-            *(--dp) = (png_byte)(255 - *(--sp));
-            *(--dp) = *(--sp);
-         }
-      }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-      else
-      {
-         /* This inverts the alpha channel in GGAA */
-         png_bytep sp  = row + row_info->rowbytes;
-         png_bytep dp = sp;
-         png_uint_32 i;
-
-         for (i = 0; i < row_width; i++)
-         {
-            *(--dp) = (png_byte)(255 - *(--sp));
-            *(--dp) = (png_byte)(255 - *(--sp));
-/*
-            *(--dp) = *(--sp);
-            *(--dp) = *(--sp);
-*/
-            sp-=2;
-            dp=sp;
-         }
-      }
-#endif
-   }
-}
-#endif
-
-#ifdef PNG_READ_FILLER_SUPPORTED
-/* Add filler channel if we have RGB color */
-void /* PRIVATE */
-png_do_read_filler(png_row_infop row_info, png_bytep row,
-    png_uint_32 filler, png_uint_32 flags)
-{
-   png_uint_32 i;
-   png_uint_32 row_width = row_info->width;
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-   png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
-#endif
-   png_byte lo_filler = (png_byte)(filler & 0xff);
-
-   png_debug(1, "in png_do_read_filler");
-
-   if (
-       row_info->color_type == PNG_COLOR_TYPE_GRAY)
-   {
-      if (row_info->bit_depth == 8)
-      {
-         if (flags & PNG_FLAG_FILLER_AFTER)
-         {
-            /* This changes the data from G to GX */
-            png_bytep sp = row + (png_size_t)row_width;
-            png_bytep dp =  sp + (png_size_t)row_width;
-            for (i = 1; i < row_width; i++)
-            {
-               *(--dp) = lo_filler;
-               *(--dp) = *(--sp);
-            }
-            *(--dp) = lo_filler;
-            row_info->channels = 2;
-            row_info->pixel_depth = 16;
-            row_info->rowbytes = row_width * 2;
-         }
-
-         else
-         {
-            /* This changes the data from G to XG */
-            png_bytep sp = row + (png_size_t)row_width;
-            png_bytep dp = sp  + (png_size_t)row_width;
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = *(--sp);
-               *(--dp) = lo_filler;
-            }
-            row_info->channels = 2;
-            row_info->pixel_depth = 16;
-            row_info->rowbytes = row_width * 2;
-         }
-      }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-      else if (row_info->bit_depth == 16)
-      {
-         if (flags & PNG_FLAG_FILLER_AFTER)
-         {
-            /* This changes the data from GG to GGXX */
-            png_bytep sp = row + (png_size_t)row_width * 2;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 1; i < row_width; i++)
-            {
-               *(--dp) = hi_filler;
-               *(--dp) = lo_filler;
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-            }
-            *(--dp) = hi_filler;
-            *(--dp) = lo_filler;
-            row_info->channels = 2;
-            row_info->pixel_depth = 32;
-            row_info->rowbytes = row_width * 4;
-         }
-
-         else
-         {
-            /* This changes the data from GG to XXGG */
-            png_bytep sp = row + (png_size_t)row_width * 2;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = hi_filler;
-               *(--dp) = lo_filler;
-            }
-            row_info->channels = 2;
-            row_info->pixel_depth = 32;
-            row_info->rowbytes = row_width * 4;
-         }
-      }
-#endif
-   } /* COLOR_TYPE == GRAY */
-   else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
-   {
-      if (row_info->bit_depth == 8)
-      {
-         if (flags & PNG_FLAG_FILLER_AFTER)
-         {
-            /* This changes the data from RGB to RGBX */
-            png_bytep sp = row + (png_size_t)row_width * 3;
-            png_bytep dp = sp  + (png_size_t)row_width;
-            for (i = 1; i < row_width; i++)
-            {
-               *(--dp) = lo_filler;
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-            }
-            *(--dp) = lo_filler;
-            row_info->channels = 4;
-            row_info->pixel_depth = 32;
-            row_info->rowbytes = row_width * 4;
-         }
-
-         else
-         {
-            /* This changes the data from RGB to XRGB */
-            png_bytep sp = row + (png_size_t)row_width * 3;
-            png_bytep dp = sp + (png_size_t)row_width;
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = lo_filler;
-            }
-            row_info->channels = 4;
-            row_info->pixel_depth = 32;
-            row_info->rowbytes = row_width * 4;
-         }
-      }
-
-#ifdef PNG_READ_16BIT_SUPPORTED
-      else if (row_info->bit_depth == 16)
-      {
-         if (flags & PNG_FLAG_FILLER_AFTER)
-         {
-            /* This changes the data from RRGGBB to RRGGBBXX */
-            png_bytep sp = row + (png_size_t)row_width * 6;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 1; i < row_width; i++)
-            {
-               *(--dp) = hi_filler;
-               *(--dp) = lo_filler;
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-            }
-            *(--dp) = hi_filler;
-            *(--dp) = lo_filler;
-            row_info->channels = 4;
-            row_info->pixel_depth = 64;
-            row_info->rowbytes = row_width * 8;
-         }
-
-         else
-         {
-            /* This changes the data from RRGGBB to XXRRGGBB */
-            png_bytep sp = row + (png_size_t)row_width * 6;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 0; i < row_width; i++)
-            {
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = *(--sp);
-               *(--dp) = hi_filler;
-               *(--dp) = lo_filler;
-            }
-
-            row_info->channels = 4;
-            row_info->pixel_depth = 64;
-            row_info->rowbytes = row_width * 8;
-         }
-      }
-#endif
-   } /* COLOR_TYPE == RGB */
-}
-#endif
-
-#ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
-/* Expand grayscale files to RGB, with or without alpha */
-void /* PRIVATE */
-png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
-{
-   png_uint_32 i;
-   png_uint_32 row_width = row_info->width;
-
-   png_debug(1, "in png_do_gray_to_rgb");
-
-   if (row_info->bit_depth >= 8 &&
-       !(row_info->color_type & PNG_COLOR_MASK_COLOR))
-   {
-      if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
-      {
-         if (row_info->bit_depth == 8)
-         {
-            /* This changes G to RGB */
-            png_bytep sp = row + (png_size_t)row_width - 1;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 0; i < row_width; i++)
-            {
-               *(dp--) = *sp;
-               *(dp--) = *sp;
-               *(dp--) = *(sp--);
-            }
-         }
-
-         else
-         {
-            /* This changes GG to RRGGBB */
-            png_bytep sp = row + (png_size_t)row_width * 2 - 1;
-            png_bytep dp = sp  + (png_size_t)row_width * 4;
-            for (i = 0; i < row_width; i++)
-            {
-               *(dp--) = *sp;
-               *(dp--) = *(sp - 1);
-               *(dp--) = *sp;
-               *(dp--) = *(sp - 1);
-               *(dp--) = *(sp--);
-               *(dp--) = *(sp--);
-            }
-         }
-      }
-
-      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
-      {
-         if (row_info->bit_depth == 8)
-         {
-            /* This changes GA to RGBA */
-            png_bytep sp = row + (png_size_t)row_width * 2 - 1;
-            png_bytep dp = sp  + (png_size_t)row_width * 2;
-            for (i = 0; i < row_width; i++)
-            {
-               *(dp--) = *(sp--);
-               *(dp--) = *sp;
-               *(dp--) = *sp;
-               *(dp--) = *(sp--);
-            }
-         }
-
-         else
-         {
-            /* This changes GGAA to RRGGBBAA */
-            png_bytep sp = row + (png_size_t)row_width * 4 - 1;
-            png_bytep dp = sp  + (png_size_t)row_width * 4;
-            for (i = 0; i < row_width; i++)
-            {
-               *(dp--) = *(sp--);
-               *(dp--) = *(sp--);
-               *(dp--) = *sp;
-               *(dp--) = *(sp - 1);
-               *(dp--) = *sp;
-               *(dp--) = *(sp - 1);
-               *(dp--) = *(sp--);
-               *(dp--) = *(sp--);
-            }
-         }
-      }
-      row_info->channels = (png_byte)(row_info->channels + 2);
-      row_info->color_type |= PNG_COLOR_MASK_COLOR;
-      row_info->pixel_depth = (png_byte)(row_info->channels *
-          row_info->bit_depth);
-      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
-   }
-}
-#endif
-
-#ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
-/* Reduce RGB files to grayscale, with or without alpha
- * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
- * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
- * versions dated 1998 through November 2002 have been archived at
- * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
- * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
- * Charles Poynton poynton at poynton.com
- *
- *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
- *
- *  which can be expressed with integers as
- *
- *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
- *
- * Poynton's current link (as of January 2003 through July 2011):
- * <http://www.poynton.com/notes/colour_and_gamma/>
- * has changed the numbers slightly:
- *
- *     Y = 0.2126*R + 0.7152*G + 0.0722*B
- *
- *  which can be expressed with integers as
- *
- *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
- *
- *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
- *  end point chromaticities and the D65 white point.  Depending on the
- *  precision used for the D65 white point this produces a variety of different
- *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
- *  used (0.3127,0.3290) the Y calculation would be:
- *
- *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
- *
- *  While this is correct the rounding results in an overflow for white, because
- *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
- *  libpng uses, instead, the closest non-overflowing approximation:
- *
- *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
- *
- *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
- *  (including an sRGB chunk) then the chromaticities are used to calculate the
- *  coefficients.  See the chunk handling in pngrutil.c for more information.
- *
- *  In all cases the calculation is to be done in a linear colorspace.  If no
- *  gamma information is available to correct the encoding of the original RGB
- *  values this results in an implicit assumption that the original PNG RGB
- *  values were linear.
- *
- *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
- *  the API takes just red and green coefficients the blue coefficient is
- *  calculated to make the sum 32768.  This will result in different rounding
- *  to that used above.
- */
-int /* PRIVATE */
-png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
-
-{
-   int rgb_error = 0;
-
-   png_debug(1, "in png_do_rgb_to_gray");
-
-   if (!(row_info->color_type & PNG_COLOR_MASK_PALETTE) &&
-       (row_info->color_type & PNG_COLOR_MASK_COLOR))
-   {
-      PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
-      PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
-      PNG_CONST png_uint_32 bc = 32768 - rc - gc;
-      PNG_CONST png_uint_32 row_width = row_info->width;
-      PNG_CONST int have_alpha =
-         (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
-
-      if (row_info->bit_depth == 8)
-      {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-         /* Notice that gamma to/from 1 are not necessarily inverses (if
-          * there is an overall gamma correction).  Prior to 1.5.5 this code
-          * checked the linearized values for equality; this doesn't match
-          * the documentation, the original values must be checked.
-          */
-         if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
-         {
-            png_bytep sp = row;
-            png_bytep dp = row;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               png_byte red   = *(sp++);
-               png_byte green = *(sp++);
-               png_byte blue  = *(sp++);
-
-               if (red != green || red != blue)
-               {
-                  red = png_ptr->gamma_to_1[red];
-                  green = png_ptr->gamma_to_1[green];
-                  blue = png_ptr->gamma_to_1[blue];
-
-                  rgb_error |= 1;
-                  *(dp++) = png_ptr->gamma_from_1[
-                      (rc*red + gc*green + bc*blue + 16384)>>15];
-               }
-
-               else
-               {
-                  /* If there is no overall correction the table will not be
-                   * set.
-                   */
-                  if (png_ptr->gamma_table != NULL)
-                     red = png_ptr->gamma_table[red];
-
-                  *(dp++) = red;
-               }
-
-               if (have_alpha)
-                  *(dp++) = *(sp++);
-            }
-         }
-         else
-#endif
-         {
-            png_bytep sp = row;
-            png_bytep dp = row;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               png_byte red   = *(sp++);
-               png_byte green = *(sp++);
-               png_byte blue  = *(sp++);
-
-               if (red != green || red != blue)
-               {
-                  rgb_error |= 1;
-                  /* NOTE: this is the historical approach which simply
-                   * truncates the results.
-                   */
-                  *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
-               }
-
-               else
-                  *(dp++) = red;
-
-               if (have_alpha)
-                  *(dp++) = *(sp++);
-            }
-         }
-      }
-
-      else /* RGB bit_depth == 16 */
-      {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-         if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
-         {
-            png_bytep sp = row;
-            png_bytep dp = row;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               png_uint_16 red, green, blue, w;
-
-               red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-               green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-               blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-
-               if (red == green && red == blue)
-               {
-                  if (png_ptr->gamma_16_table != NULL)
-                     w = png_ptr->gamma_16_table[(red&0xff)
-                         >> png_ptr->gamma_shift][red>>8];
-
-                  else
-                     w = red;
-               }
-
-               else
-               {
-                  png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
-                      >> png_ptr->gamma_shift][red>>8];
-                  png_uint_16 green_1 =
-                      png_ptr->gamma_16_to_1[(green&0xff) >>
-                      png_ptr->gamma_shift][green>>8];
-                  png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
-                      >> png_ptr->gamma_shift][blue>>8];
-                  png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
-                      + bc*blue_1 + 16384)>>15);
-                  w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
-                      png_ptr->gamma_shift][gray16 >> 8];
-                  rgb_error |= 1;
-               }
-
-               *(dp++) = (png_byte)((w>>8) & 0xff);
-               *(dp++) = (png_byte)(w & 0xff);
-
-               if (have_alpha)
-               {
-                  *(dp++) = *(sp++);
-                  *(dp++) = *(sp++);
-               }
-            }
-         }
-         else
-#endif
-         {
-            png_bytep sp = row;
-            png_bytep dp = row;
-            png_uint_32 i;
-
-            for (i = 0; i < row_width; i++)
-            {
-               png_uint_16 red, green, blue, gray16;
-
-               red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-               green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-               blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
-
-               if (red != green || red != blue)
-                  rgb_error |= 1;
-
-               /* From 1.5.5 in the 16 bit case do the accurate conversion even
-                * in the 'fast' case - this is because this is where the code
-                * ends up when handling linear 16 bit data.
-                */
-               gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
-                  15);
-               *(dp++) = (png_byte)((gray16>>8) & 0xff);
-               *(dp++) = (png_byte)(gray16 & 0xff);
-
-               if (have_alpha)
-               {
-                  *(dp++) = *(sp++);
-                  *(dp++) = *(sp++);
-               }
-            }
-         }
-      }
-
-      row_info->channels = (png_byte)(row_info->channels - 2);
-      row_info->color_type = (png_byte)(row_info->color_type &
-          ~PNG_COLOR_MASK_COLOR);
-      row_info->pixel_depth = (png_byte)(row_info->channels *
-          row_info->bit_depth);
-      row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
-   }
-   return rgb_error;
-}
-#endif
-#endif /* PNG_READ_TRANSFORMS_SUPPORTED */
-
-#ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED
-/* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
- * large of png_color.  This lets grayscale images be treated as
- * paletted.  Most useful for gamma correction and simplification
- * of code.  This API is not used internally.
- */
-void PNGAPI
-png_build_grayscale_palette(int bit_depth, png_colorp palette)
-{
-   int num_palette;
-   int color_inc;
-   int i;
-   int v;
-
-   png_debug(1, "in png_do_build_grayscale_palette");
-
-   if (palette == NULL)
-      return;
-
-   switch (bit_depth)
-   {
-      case 1:
-         num_palette = 2;
-         color_inc = 0xff;
-         break;
-
-      case 2:
-         num_palette = 4;
-         color_inc = 0x55;
-         break;
-
-      case 4:
-         num_palette = 16;
-         color_inc = 0x11;
-         break;
-
-      case 8:
-         num_palette = 256;
-         color_inc = 1;
-         break;
-
-      default:
-         num_palette = 0;
-         color_inc = 0;
-         break;
-   }
-
-   for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
-   {
-      palette[i].red = (png_byte)v;
-      palette[i].green = (png_byte)v;
-      palette[i].blue = (png_byte)v;
-   }
-}
-#endif
-
-
-#ifdef PNG_READ_TRANSFORMS_SUPPORTED
-#if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
-   defined(PNG_READ_ALPHA_MODE_SUPPORTED)
-/* Replace any alpha or transparency with the supplied background color.
- * "background" is already in the screen gamma, while "background_1" is
- * at a gamma of 1.0.  Paletted files have already been taken care of.
- */
-void /* PRIVATE */
-png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
-{
-#ifdef PNG_READ_GAMMA_SUPPORTED
-   png_const_bytep gamma_table = png_ptr->gamma_table;
-   png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
-   png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
-   png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
-   png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
-   png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
-   int gamma_shift = png_ptr->gamma_shift;
-   int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
-#endif
-
-   png_bytep sp;
-   png_uint_32 i;
-   png_uint_32 row_width = row_info->width;
-   int shift;
-
-   png_debug(1, "in png_do_compose");
-
-   {
-      switch (row_info->color_type)
-      {
-         case PNG_COLOR_TYPE_GRAY:
-         {
-            switch (row_info->bit_depth)
-            {
-               case 1:
-               {
-                  sp = row;
-                  shift = 7;
-                  for (i = 0; i < row_width; i++)
-                  {
-                     if ((png_uint_16)((*sp >> shift) & 0x01)
-                        == png_ptr->trans_color.gray)
-                     {
-                        unsigned int tmp = *sp & (0x7f7f >> (7 - shift));
-                        tmp |= png_ptr->background.gray << shift;
-                        *sp = (png_byte)(tmp & 0xff);
-                     }
-
-                     if (!shift)
-                     {
-                        shift = 7;
-                        sp++;
-                     }
-
-                     else
-                        shift--;
-                  }
-                  break;
-               }
-
-               case 2:
-               {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-                  if (gamma_table != NULL)
-                  {
-                     sp = row;
-                     shift = 6;
-                     for (i = 0; i < row_width; i++)
-                     {
-                        if ((png_uint_16)((*sp >> shift) & 0x03)
-                            == png_ptr->trans_color.gray)
-                        {
-                           unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
-                           tmp |= png_ptr->background.gray << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        else
-                        {
-                           unsigned int p = (*sp >> shift) & 0x03;
-                           unsigned int g = (gamma_table [p | (p << 2) |
-                               (p << 4) | (p << 6)] >> 6) & 0x03;
-                           unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
-                           tmp |= g << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        if (!shift)
-                        {
-                           shift = 6;
-                           sp++;
-                        }
-
-                        else
-                           shift -= 2;
-                     }
-                  }
-
-                  else
-#endif
-                  {
-                     sp = row;
-                     shift = 6;
-                     for (i = 0; i < row_width; i++)
-                     {
-                        if ((png_uint_16)((*sp >> shift) & 0x03)
-                            == png_ptr->trans_color.gray)
-                        {
-                           unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
-                           tmp |= png_ptr->background.gray << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        if (!shift)
-                        {
-                           shift = 6;
-                           sp++;
-                        }
-
-                        else
-                           shift -= 2;
-                     }
-                  }
-                  break;
-               }
-
-               case 4:
-               {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-                  if (gamma_table != NULL)
-                  {
-                     sp = row;
-                     shift = 4;
-                     for (i = 0; i < row_width; i++)
-                     {
-                        if ((png_uint_16)((*sp >> shift) & 0x0f)
-                            == png_ptr->trans_color.gray)
-                        {
-                           unsigned int tmp = *sp & (0xf0f >> (4 - shift));
-                           tmp |= png_ptr->background.gray << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        else
-                        {
-                           unsigned int p = (*sp >> shift) & 0x0f;
-                           unsigned int g = (gamma_table[p | (p << 4)] >> 4) &
-                              0x0f;
-                           unsigned int tmp = *sp & (0xf0f >> (4 - shift));
-                           tmp |= g << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        if (!shift)
-                        {
-                           shift = 4;
-                           sp++;
-                        }
-
-                        else
-                           shift -= 4;
-                     }
-                  }
-
-                  else
-#endif
-                  {
-                     sp = row;
-                     shift = 4;
-                     for (i = 0; i < row_width; i++)
-                     {
-                        if ((png_uint_16)((*sp >> shift) & 0x0f)
-                            == png_ptr->trans_color.gray)
-                        {
-                           unsigned int tmp = *sp & (0xf0f >> (4 - shift));
-                           tmp |= png_ptr->background.gray << shift;
-                           *sp = (png_byte)(tmp & 0xff);
-                        }
-
-                        if (!shift)
-                        {
-                           shift = 4;
-                           sp++;
-                        }
-
-                        else
-                           shift -= 4;
-                     }
-                  }
-                  break;
-               }
-
-               case 8:
-               {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-                  if (gamma_table != NULL)
-                  {
-                     sp = row;
-                     for (i = 0; i < row_width; i++, sp++)
-                     {
-                        if (*sp == png_ptr->trans_color.gray)
-                           *sp = (png_byte)png_ptr->background.gray;
-
-                        else
-                           *sp = gamma_table[*sp];
-                     }
-                  }
-                  else
-#endif
-                  {
-                     sp = row;
-                     for (i = 0; i < row_width; i++, sp++)
-                     {
-                        if (*sp == png_ptr->trans_color.gray)
-                           *sp = (png_byte)png_ptr->background.gray;
-                     }
-                  }
-                  break;
-               }
-
-               case 16:
-               {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-                  if (gamma_16 != NULL)
-                  {
-                     sp = row;
-                     for (i = 0; i < row_width; i++, sp += 2)
-                     {
-                        png_uint_16 v;
-
-                        v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-
-                        if (v == png_ptr->trans_color.gray)
-                        {
-                           /* Background is already in screen gamma */
-                           *sp = (png_byte)((png_ptr->background.gray >> 8)
-                                & 0xff);
-                           *(sp + 1) = (png_byte)(png_ptr->background.gray
-                                & 0xff);
-                        }
-
-                        else
-                        {
-                           v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                           *sp = (png_byte)((v >> 8) & 0xff);
-                           *(sp + 1) = (png_byte)(v & 0xff);
-                        }
-                     }
-                  }
-                  else
-#endif
-                  {
-                     sp = row;
-                     for (i = 0; i < row_width; i++, sp += 2)
-                     {
-                        png_uint_16 v;
-
-                        v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-
-                        if (v == png_ptr->trans_color.gray)
-                        {
-                           *sp = (png_byte)((png_ptr->background.gray >> 8)
-                                & 0xff);
-                           *(sp + 1) = (png_byte)(png_ptr->background.gray
-                                & 0xff);
-                        }
-                     }
-                  }
-                  break;
-               }
-
-               default:
-                  break;
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_RGB:
-         {
-            if (row_info->bit_depth == 8)
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_table != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 3)
-                  {
-                     if (*sp == png_ptr->trans_color.red &&
-                         *(sp + 1) == png_ptr->trans_color.green &&
-                         *(sp + 2) == png_ptr->trans_color.blue)
-                     {
-                        *sp = (png_byte)png_ptr->background.red;
-                        *(sp + 1) = (png_byte)png_ptr->background.green;
-                        *(sp + 2) = (png_byte)png_ptr->background.blue;
-                     }
-
-                     else
-                     {
-                        *sp = gamma_table[*sp];
-                        *(sp + 1) = gamma_table[*(sp + 1)];
-                        *(sp + 2) = gamma_table[*(sp + 2)];
-                     }
-                  }
-               }
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 3)
-                  {
-                     if (*sp == png_ptr->trans_color.red &&
-                         *(sp + 1) == png_ptr->trans_color.green &&
-                         *(sp + 2) == png_ptr->trans_color.blue)
-                     {
-                        *sp = (png_byte)png_ptr->background.red;
-                        *(sp + 1) = (png_byte)png_ptr->background.green;
-                        *(sp + 2) = (png_byte)png_ptr->background.blue;
-                     }
-                  }
-               }
-            }
-            else /* if (row_info->bit_depth == 16) */
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_16 != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 6)
-                  {
-                     png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-
-                     png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
-                         + *(sp + 3));
-
-                     png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
-                         + *(sp + 5));
-
-                     if (r == png_ptr->trans_color.red &&
-                         g == png_ptr->trans_color.green &&
-                         b == png_ptr->trans_color.blue)
-                     {
-                        /* Background is already in screen gamma */
-                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
-                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
-                                & 0xff);
-                        *(sp + 3) = (png_byte)(png_ptr->background.green
-                                & 0xff);
-                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
-                                & 0xff);
-                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
-                     }
-
-                     else
-                     {
-                        png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                        *sp = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(v & 0xff);
-
-                        v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
-                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(v & 0xff);
-
-                        v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
-                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(v & 0xff);
-                     }
-                  }
-               }
-
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 6)
-                  {
-                     png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-
-                     png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
-                         + *(sp + 3));
-
-                     png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
-                         + *(sp + 5));
-
-                     if (r == png_ptr->trans_color.red &&
-                         g == png_ptr->trans_color.green &&
-                         b == png_ptr->trans_color.blue)
-                     {
-                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
-                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
-                                & 0xff);
-                        *(sp + 3) = (png_byte)(png_ptr->background.green
-                                & 0xff);
-                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
-                                & 0xff);
-                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
-                     }
-                  }
-               }
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_GRAY_ALPHA:
-         {
-            if (row_info->bit_depth == 8)
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
-                   gamma_table != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 2)
-                  {
-                     png_uint_16 a = *(sp + 1);
-
-                     if (a == 0xff)
-                        *sp = gamma_table[*sp];
-
-                     else if (a == 0)
-                     {
-                        /* Background is already in screen gamma */
-                        *sp = (png_byte)png_ptr->background.gray;
-                     }
-
-                     else
-                     {
-                        png_byte v, w;
-
-                        v = gamma_to_1[*sp];
-                        png_composite(w, v, a, png_ptr->background_1.gray);
-                        if (!optimize)
-                           w = gamma_from_1[w];
-                        *sp = w;
-                     }
-                  }
-               }
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 2)
-                  {
-                     png_byte a = *(sp + 1);
-
-                     if (a == 0)
-                        *sp = (png_byte)png_ptr->background.gray;
-
-                     else if (a < 0xff)
-                        png_composite(*sp, *sp, a, png_ptr->background.gray);
-                  }
-               }
-            }
-            else /* if (png_ptr->bit_depth == 16) */
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
-                   gamma_16_to_1 != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 4)
-                  {
-                     png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
-                         + *(sp + 3));
-
-                     if (a == (png_uint_16)0xffff)
-                     {
-                        png_uint_16 v;
-
-                        v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                        *sp = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(v & 0xff);
-                     }
-
-                     else if (a == 0)
-                     {
-                        /* Background is already in screen gamma */
-                        *sp = (png_byte)((png_ptr->background.gray >> 8)
-                                & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
-                     }
-
-                     else
-                     {
-                        png_uint_16 g, v, w;
-
-                        g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
-                        png_composite_16(v, g, a, png_ptr->background_1.gray);
-                        if (optimize)
-                           w = v;
-                        else
-                           w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
-                        *sp = (png_byte)((w >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(w & 0xff);
-                     }
-                  }
-               }
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 4)
-                  {
-                     png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
-                         + *(sp + 3));
-
-                     if (a == 0)
-                     {
-                        *sp = (png_byte)((png_ptr->background.gray >> 8)
-                                & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
-                     }
-
-                     else if (a < 0xffff)
-                     {
-                        png_uint_16 g, v;
-
-                        g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                        png_composite_16(v, g, a, png_ptr->background.gray);
-                        *sp = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(v & 0xff);
-                     }
-                  }
-               }
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_RGB_ALPHA:
-         {
-            if (row_info->bit_depth == 8)
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
-                   gamma_table != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 4)
-                  {
-                     png_byte a = *(sp + 3);
-
-                     if (a == 0xff)
-                     {
-                        *sp = gamma_table[*sp];
-                        *(sp + 1) = gamma_table[*(sp + 1)];
-                        *(sp + 2) = gamma_table[*(sp + 2)];
-                     }
-
-                     else if (a == 0)
-                     {
-                        /* Background is already in screen gamma */
-                        *sp = (png_byte)png_ptr->background.red;
-                        *(sp + 1) = (png_byte)png_ptr->background.green;
-                        *(sp + 2) = (png_byte)png_ptr->background.blue;
-                     }
-
-                     else
-                     {
-                        png_byte v, w;
-
-                        v = gamma_to_1[*sp];
-                        png_composite(w, v, a, png_ptr->background_1.red);
-                        if (!optimize) w = gamma_from_1[w];
-                        *sp = w;
-
-                        v = gamma_to_1[*(sp + 1)];
-                        png_composite(w, v, a, png_ptr->background_1.green);
-                        if (!optimize) w = gamma_from_1[w];
-                        *(sp + 1) = w;
-
-                        v = gamma_to_1[*(sp + 2)];
-                        png_composite(w, v, a, png_ptr->background_1.blue);
-                        if (!optimize) w = gamma_from_1[w];
-                        *(sp + 2) = w;
-                     }
-                  }
-               }
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 4)
-                  {
-                     png_byte a = *(sp + 3);
-
-                     if (a == 0)
-                     {
-                        *sp = (png_byte)png_ptr->background.red;
-                        *(sp + 1) = (png_byte)png_ptr->background.green;
-                        *(sp + 2) = (png_byte)png_ptr->background.blue;
-                     }
-
-                     else if (a < 0xff)
-                     {
-                        png_composite(*sp, *sp, a, png_ptr->background.red);
-
-                        png_composite(*(sp + 1), *(sp + 1), a,
-                            png_ptr->background.green);
-
-                        png_composite(*(sp + 2), *(sp + 2), a,
-                            png_ptr->background.blue);
-                     }
-                  }
-               }
-            }
-            else /* if (row_info->bit_depth == 16) */
-            {
-#ifdef PNG_READ_GAMMA_SUPPORTED
-               if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
-                   gamma_16_to_1 != NULL)
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 8)
-                  {
-                     png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
-                         << 8) + (png_uint_16)(*(sp + 7)));
-
-                     if (a == (png_uint_16)0xffff)
-                     {
-                        png_uint_16 v;
-
-                        v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
-                        *sp = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(v & 0xff);
-
-                        v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
-                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(v & 0xff);
-
-                        v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
-                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(v & 0xff);
-                     }
-
-                     else if (a == 0)
-                     {
-                        /* Background is already in screen gamma */
-                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
-                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
-                                & 0xff);
-                        *(sp + 3) = (png_byte)(png_ptr->background.green
-                                & 0xff);
-                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
-                                & 0xff);
-                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
-                     }
-
-                     else
-                     {
-                        png_uint_16 v, w;
-
-                        v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
-                        png_composite_16(w, v, a, png_ptr->background_1.red);
-                        if (!optimize)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
-                                8];
-                        *sp = (png_byte)((w >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(w & 0xff);
-
-                        v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
-                        png_composite_16(w, v, a, png_ptr->background_1.green);
-                        if (!optimize)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
-                                8];
-
-                        *(sp + 2) = (png_byte)((w >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(w & 0xff);
-
-                        v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
-                        png_composite_16(w, v, a, png_ptr->background_1.blue);
-                        if (!optimize)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
-                                8];
-
-                        *(sp + 4) = (png_byte)((w >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(w & 0xff);
-                     }
-                  }
-               }
-
-               else
-#endif
-               {
-                  sp = row;
-                  for (i = 0; i < row_width; i++, sp += 8)
-                  {
-                     png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
-                         << 8) + (png_uint_16)(*(sp + 7)));
-
-                     if (a == 0)
-                     {
-                        *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
-                        *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
-                                & 0xff);
-                        *(sp + 3) = (png_byte)(png_ptr->background.green
-                                & 0xff);
-                        *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
-                                & 0xff);
-                        *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
-                     }
-
-                     else if (a < 0xffff)
-                     {
-                        png_uint_16 v;
-
-                        png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
-                        png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
-                            + *(sp + 3));
-                        png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
-                            + *(sp + 5));
-
-                        png_composite_16(v, r, a, png_ptr->background.red);
-                        *sp = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 1) = (png_byte)(v & 0xff);
-
-                        png_composite_16(v, g, a, png_ptr->background.green);
-                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 3) = (png_byte)(v & 0xff);
-
-                        png_composite_16(v, b, a, png_ptr->background.blue);
-                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
-                        *(sp + 5) = (png_byte)(v & 0xff);
-                     }
-                  }
-               }
-            }
-            break;
-         }
-
-         default:
-            break;
-      }
-   }
-}
-#endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */
-
-#ifdef PNG_READ_GAMMA_SUPPORTED
-/* Gamma correct the image, avoiding the alpha channel.  Make sure
- * you do this after you deal with the transparency issue on grayscale
- * or RGB images. If your bit depth is 8, use gamma_table, if it
- * is 16, use gamma_16_table and gamma_shift.  Build these with
- * build_gamma_table().
- */
-void /* PRIVATE */
-png_do_gamma(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
-{
-   png_const_bytep gamma_table = png_ptr->gamma_table;
-   png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
-   int gamma_shift = png_ptr->gamma_shift;
-
-   png_bytep sp;
-   png_uint_32 i;
-   png_uint_32 row_width=row_info->width;
-
-   png_debug(1, "in png_do_gamma");
-
-   if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
-       (row_info->bit_depth == 16 && gamma_16_table != NULL)))
-   {
-      switch (row_info->color_type)
-      {
-         case PNG_COLOR_TYPE_RGB:
-         {
-            if (row_info->bit_depth == 8)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  *sp = gamma_table[*sp];
-                  sp++;
-                  *sp = gamma_table[*sp];
-                  sp++;
-                  *sp = gamma_table[*sp];
-                  sp++;
-               }
-            }
-
-            else /* if (row_info->bit_depth == 16) */
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 v;
-
-                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-
-                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-
-                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-               }
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_RGB_ALPHA:
-         {
-            if (row_info->bit_depth == 8)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  *sp = gamma_table[*sp];
-                  sp++;
-
-                  *sp = gamma_table[*sp];
-                  sp++;
-
-                  *sp = gamma_table[*sp];
-                  sp++;
-
-                  sp++;
-               }
-            }
-
-            else /* if (row_info->bit_depth == 16) */
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-
-                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-
-                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 4;
-               }
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_GRAY_ALPHA:
-         {
-            if (row_info->bit_depth == 8)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  *sp = gamma_table[*sp];
-                  sp += 2;
-               }
-            }
-
-            else /* if (row_info->bit_depth == 16) */
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 4;
-               }
-            }
-            break;
-         }
-
-         case PNG_COLOR_TYPE_GRAY:
-         {
-            if (row_info->bit_depth == 2)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i += 4)
-               {
-                  int a = *sp & 0xc0;
-                  int b = *sp & 0x30;
-                  int c = *sp & 0x0c;
-                  int d = *sp & 0x03;
-
-                  *sp = (png_byte)(
-                      ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
-                      ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
-                      ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
-                      ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
-                  sp++;
-               }
-            }
-
-            if (row_info->bit_depth == 4)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i += 2)
-               {
-                  int msb = *sp & 0xf0;
-                  int lsb = *sp & 0x0f;
-
-                  *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
-                      | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
-                  sp++;
-               }
-            }
-
-            else if (row_info->bit_depth == 8)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  *sp = gamma_table[*sp];
-                  sp++;
-               }
-            }
-
-            else if (row_info->bit_depth == 16)
-            {
-               sp = row;
-               for (i = 0; i < row_width; i++)
-               {
-                  png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
-                  *sp = (png_byte)((v >> 8) & 0xff);
-                  *(sp + 1) = (png_byte)(v & 0xff);
-                  sp += 2;
-               }
-            }
-            break;
-         }
-
-         default:
-            break;
-      }
-   }
-}
-#endif
-
-#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
-/* Encode the alpha channel to the output gamma (the input channel is always
- * linear.)  Called only with color types that have an alpha channel.  Needs the
- * from_1 tables.
- */
-void /* PRIVATE */
-png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
-{
-   png_uint_32 row_width = row_info->width;
-
-   png_debug(1, "in png_do_encode_alpha");
-
-   if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
-   {
-      if (row_info->bit_depth == 8)
-      {
-         PNG_CONST png_bytep table = png_ptr->gamma_from_1;
-
-         if (table != NULL)
-         {
-            PNG_CONST int step =
-               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
-
-            /* The alpha channel is the last component: */
-            row += step - 1;
-
-            for (; row_width > 0; --row_width, row += step)
-               *row = table[*row];
-
-            return;
-         }
-      }
-
-      else if (row_info->bit_depth == 16)
-      {
-         PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
-         PNG_CONST int gamma_shift = png_ptr->gamma_shift;
-
-         if (table != NULL)
-         {
-            PNG_CONST int step =
-               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
-
-            /* The alpha channel is the last component: */
-            row += step - 2;
-
-            for (; row_width > 0; --row_width, row += step)
-            {
-               png_uint_16 v;
-
-               v = table[*(row + 1) >> gamma_shift][*row];
-               *row = (png_byte)((v >> 8) & 0xff);
-               *(row + 1) = (png_byte)(v & 0xff);
-            }
-
-            return;
-         }
-      }
-   }
-
-   /* Only get to here if called with a weird row_info; no harm has been done,
-    * so just issue a warning.
-    */
-   png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
-}
-#endif
-
-#ifdef PNG_READ_EXPAND_SUPPORTED
-/* Expands a palette row to an RGB or RGBA row depending
- * upon whether you supply trans and num_trans.
- */
-void /* PRIVATE */
-png_do_expand_palette(png_row_infop row_info, png_bytep row,
-   png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
-{
-   int shift, value;
-   png_bytep sp, dp;
-   png_uint_32 i;
-   png_uint_32 row_width=row_info->width;
-
-   png_debug(1, "in png_do_expand_palette");
-
-   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
-   {
-      if (row_info->bit_depth < 8)
-      {
-         switch (row_info->bit_depth)
-         {
-            case 1:
-            {
-               sp = row + (png_size_t)((row_width - 1) >> 3);
-               dp = row + (png_size_t)row_width - 1;
-               shift = 7 - (int)((row_width + 7) & 0x07);
-               for (i = 0; i < row_width; i++)
-               {
-                  if ((*sp >> shift) & 0x01)
-                     *dp = 1;
-
-                  else
-                     *dp = 0;
-
-                  if (shift == 7)
-                  {
-                     shift = 0;
-                     sp--;
-                  }
-
-                  else
-                     shift++;
-
-                  dp--;
-               }
-               break;
-            }
-
-            case 2:
-            {
-               sp = row + (png_size_t)((row_width - 1) >> 2);
-               dp = row + (png_size_t)row_width - 1;
-               shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
-               for (i = 0; i < row_width; i++)
-               {
-                  value = (*sp >> shift) & 0x03;
-                  *dp = (png_byte)value;
-                  if (shift == 6)
-                  {
-                     shift = 0;
-                     sp--;
-                  }
-
-                  else
-                     shift += 2;
-
-                  dp--;
-               }
-               break;
-            }
-
-            case 4:
-            {
-               sp = row + (png_size_t)((row_width - 1) >> 1);
-               dp = row + (png_size_t)row_width - 1;
-               shift = (int)((row_width & 0x01) << 2);
-               for (i = 0; i < row_width; i++)
-               {
-                  value = (*sp >> shift) & 0x0f;
-                  *dp = (png_byte)value;
-                  if (shift == 4)
-                  {
-                     shift = 0;
-                     sp--;
-                  }
-
-                  else
-                     shift += 4;
-
-                  dp--;
-               }
-               break;
-            }
-
-            default:
-               break;
-         }
-         row_info->bit_depth = 8;
-         row_info->pixel_depth = 8;
-         row_info->rowbytes = row_width;
-      }
-
-      if (row_info->bit_depth == 8)
-      {
-         {
-            if (num_trans > 0)
-            {
-               sp = row + (png_size_t)row_width - 1;
-               dp = row + (png_size_t)(row_width << 2) - 1;
-
-               for (i = 0; i < row_width; i++)
-               {
-                  if ((int)(*sp) >= num_trans)
-                     *dp-- = 0xff;
-
-                  else
-                     *dp-- = trans_alpha[*sp];
-
-                  *dp-- = palette[*sp].blue;
-                  *dp-- = palette[*sp].green;
-                  *dp-- = palette[*sp].red;
-                  sp--;
-               }
-               row_info->bit_depth = 8;
-               row_info->pixel_depth = 32;
-               row_info->rowbytes = row_width * 4;
-               row_info->color_type = 6;
-               row_info->channels = 4;
-            }
-
-            else
-            {
-               sp = row + (png_size_t)row_width - 1;
-               dp = row + (png_size_t)(row_width * 3) - 1;
-
-               for (i = 0; i < row_width; i++)
-               {
-                  *dp-- = palette[*sp].blue;
-                  *dp-- = palette[*sp].green;
-                  *dp-- = palette[*sp].red;
-                  sp--;
-               }
-
-               row_info->bit_depth = 8;
-               row_info->pixel_depth = 24;
-               row_info->rowbytes = row_width * 3;
-               row_info->color_type = 2;
-               row_info->channels = 3;
-            }
-         }
-      }
-   }
-}
-
-/* If the bit depth < 8, it is expanded to 8.  Also, if the already
- * expanded transparency value is supplied, an alpha channel is built.
- */
-void /* PRIVATE */
-png_do_expand(png_row_infop row_info, png_bytep row,
-    png_const_color_16p trans_color)
-{
-   int shift, value;
-   png_bytep sp, dp;
-   png_uint_32 i;
-   png_uint_32 row_width=row_info->width;
-
-   png_debug(1, "in png_do_expand");
-
-   {
-      if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
-      {
-         unsigned int gray = trans_color ? trans_color->gray : 0;
-
-         if (row_info->bit_depth < 8)
-         {
-            switch (row_info->bit_depth)
-            {
-               case 1:
-               {
-                  gray = (gray & 0x01) * 0xff;
-                  sp = row + (png_size_t)((row_width - 1) >> 3);
-                  dp = row + (png_size_t)row_width - 1;
-                  shift = 7 - (int)((row_width + 7) & 0x07);
-                  for (i = 0; i < row_width; i++)
-                  {
-                     if ((*sp >> shift) & 0x01)
-                        *dp = 0xff;
-
-                     else
-                        *dp = 0;
-
-                     if (shift == 7)
-                     {
-                        shift = 0;
-                        sp--;
-                     }
-
-                     else
-                        shift++;
-
-                     dp--;
-                  }
-                  break;
-               }
-
-               case 2:
-               {
-                  gray = (gray & 0x03) * 0x55;
-                  sp = row + (png_size_t)((row_width - 1) >> 2);
-                  dp = row + (png_size_t)row_width - 1;
-                  shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
-                  for (i = 0; i < row_width; i++)
-                  {
-                     value = (*sp >> shift) & 0x03;
-                     *dp = (png_byte)(value | (value << 2) | (value << 4) |
-                        (value << 6));
-                     if (shift == 6)
-                     {
-                        shift = 0;
-                        sp--;
-                     }
-
-                     else
-                        shift += 2;
-
-                     dp--;
-                  }
-                  break;
-               }
-
-               case 4:
-               {
-                  gray = (gray & 0x0f) * 0x11;
-                  sp = row + (png_size_t)((row_width - 1) >> 1);
-                  dp = row + (png_size_t)row_width - 1;
-                  shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
-                  for (i = 0; i < row_width; i++)
-                  {
-                     value = (*sp >> shift) & 0x0f;
-                     *dp = (png_byte)(value | (value << 4));
-                     if (shift == 4)
-                     {
-                        shift = 0;
-                        sp--;
-                     }
-
-                     else
-                        shift = 4;
-
-                     dp--;
-                  }
-                  break;
-               }
-
-               default:
-                  break;
-            }
-
-            row_info->bit_depth = 8;
-            row_info->pixel_depth = 8;
-            row_info->rowbytes = row_width;
-         }
-
-         if (trans_color != NULL)
-         {
-            if (row_info->bit_depth == 8)
-            {
-               gray = gray & 0xff;
-               sp = row + (png_size_t)row_width - 1;
-               dp = row + (png_size_t)(row_width << 1) - 1;
-
-               for (i = 0; i < row_width; i++)
-               {
-                  if (*sp == gray)
-                     *dp-- = 0;
-
-                  else
-                     *dp-- = 0xff;
-
-                  *dp-- = *sp--;
-               }
-            }
-
-            else if (row_info->bit_depth == 16)
-            {
-               unsigned int gray_high = (gray >> 8) & 0xff;
-               unsigned int gray_low = gray & 0xff;
-               sp = row + row_info->rowbytes - 1;
-               dp = row + (row_info->rowbytes << 1) - 1;
-               for (i = 0; i < row_width; i++)
-               {
-                  if (*(sp - 1) == gray_high && *(sp) == gray_low)
-                  {
-                     *dp-- = 0;
-                     *dp-- = 0;
-                  }
-
-                  else
-                  {
-                     *dp-- = 0xff;
-                     *dp-- = 0xff;
-                  }
-
-                  *dp-- = *sp--;
-                  *dp-- = *sp--;
-               }
-            }
-
-            row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
-            row_info->channels = 2;
-            row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
-            row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
-               row_width);
-         }
-      }
-      else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_color)
-      {
-         if (row_info->bit_depth == 8)
-         {
-            png_byte red = (png_byte)(trans_color->red & 0xff);
-            png_byte green = (png_byte)(trans_color->green & 0xff);
-            png_byte blue = (png_byte)(trans_color->blue & 0xff);
-            sp = row + (png_size_t)row_info->rowbytes - 1;
-            dp = row + (png_size_t)(row_width << 2) - 1;
-            for (i = 0; i < row_width; i++)
-            {
-               if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
-                  *dp-- = 0;
-
-               else
-                  *dp-- = 0xff;
-
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-            }
-         }
-         else if (row_info->bit_depth == 16)
-         {
-            png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
-            png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
-            png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
-            png_byte red_low = (png_byte)(trans_color->red & 0xff);
-            png_byte green_low = (png_byte)(trans_color->green & 0xff);
-            png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
-            sp = row + row_info->rowbytes - 1;
-            dp = row + (png_size_t)(row_width << 3) - 1;
-            for (i = 0; i < row_width; i++)
-            {
-               if (*(sp - 5) == red_high &&
-                   *(sp - 4) == red_low &&
-                   *(sp - 3) == green_high &&
-                   *(sp - 2) == green_low &&
-                   *(sp - 1) == blue_high &&
-                   *(sp    ) == blue_low)
-               {
-                  *dp-- = 0;
-                  *dp-- = 0;
-               }
-
-               else
-               {
-                  *dp-- = 0xff;
-                  *dp-- = 0xff;
-               }
-
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-               *dp-- = *sp--;
-            }
-         }
-         row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
-         row_info->channels = 4;
-         row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
-      }
-   }
-}
-#endif
-
-#ifdef PNG_READ_EXPAND_16_SUPPORTED
-/* If the bit depth is 8 and the color type is not a palette type expand the
- * whole row to 16 bits.  Has no effect otherwise.
- */
-void /* PRIVATE */
-png_do_expand_16(png_row_infop row_info, png_bytep row)
-{
-   if (row_info->bit_depth == 8 &&
-      row_info->color_type != PNG_COLOR_TYPE_PALETTE)
-   {
-      /* The row have a sequence of bytes containing [0..255] and we need
-       * to turn it into another row containing [0..65535], to do this we
-       * calculate:
-       *
-       *  (input / 255) * 65535
-       *
-       *  Which happens to be exactly input * 257 and this can be achieved
-       *  simply by byte replication in place (copying backwards).
-       */
-      png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
-      png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
-      while (dp > sp)
-         dp[-2] = dp[-1] = *--sp, dp -= 2;
-
-      row_info->rowbytes *= 2;
-      row_info->bit_depth = 16;
-      row_info->pixel_depth = (png_byte)(row_info->channels * 16);
-   }
-}
-#endif
-
-#ifdef PNG_READ_QUANTIZE_SUPPORTED
-void /* PRIVATE */
-png_do_quantize(png_row_infop row_info, png_bytep row,
-    png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
-{
-   png_bytep sp, dp;
-   png_uint_32 i;
-   png_uint_32 row_width=row_info->width;
-
-   png_debug(1, "in png_do_quantize");
-
-   if (row_info->bit_depth == 8)
-   {
-      if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
-      {
-         int r, g, b, p;
-         sp = row;
-         dp = row;
-         for (i = 0; i < row_width; i++)
-         {
-            r = *sp++;
-            g = *sp++;
-            b = *sp++;
-
-            /* This looks real messy, but the compiler will reduce
-             * it down to a reasonable formula.  For example, with
-             * 5 bits per color, we get:
-             * p = (((r >> 3) & 0x1f) << 10) |
-             *    (((g >> 3) & 0x1f) << 5) |
-             *    ((b >> 3) & 0x1f);
-             */
-            p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
-                ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
-                (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
-                (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
-                ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
-                (PNG_QUANTIZE_BLUE_BITS)) |
-                ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
-                ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
-
-            *dp++ = palette_lookup[p];
-         }
-
-         row_info->color_type = PNG_COLOR_TYPE_PALETTE;
-         row_info->channels = 1;
-         row_info->pixel_depth = row_info->bit_depth;
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
-      }
-
-      else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
-         palette_lookup != NULL)
-      {
-         int r, g, b, p;
-         sp = row;
-         dp = row;
-         for (i = 0; i < row_width; i++)
-         {
-            r = *sp++;
-            g = *sp++;
-            b = *sp++;
-            sp++;
-
-            p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
-                ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
-                (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
-                (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
-                ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
-                (PNG_QUANTIZE_BLUE_BITS)) |
-                ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
-                ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
-
-            *dp++ = palette_lookup[p];
-         }
-
-         row_info->color_type = PNG_COLOR_TYPE_PALETTE;
-         row_info->channels = 1;
-         row_info->pixel_depth = row_info->bit_depth;
-         row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
-      }
-
-      else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
-         quantize_lookup)
-      {
-         sp = row;
-
-         for (i = 0; i < row_width; i++, sp++)
-         {
-            *sp = quantize_lookup[*sp];
-         }
-      }
-   }
-}
-#endif /* PNG_READ_QUANTIZE_SUPPORTED */
-#endif /* PNG_READ_TRANSFORMS_SUPPORTED */
-
-#ifdef PNG_MNG_FEATURES_SUPPORTED
-/* Undoes intrapixel differencing  */
-void /* PRIVATE */
-png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
-{
-   png_debug(1, "in png_do_read_intrapixel");
-
-   if (
-       (row_info->color_type & PNG_COLOR_MASK_COLOR))
-   {
-      int bytes_per_pixel;
-      png_uint_32 row_width = row_info->width;
-
-      if (row_info->bit_depth == 8)
-      {
-         png_bytep rp;
-         png_uint_32 i;
-
-         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
-            bytes_per_pixel = 3;
-
-         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
-            bytes_per_pixel = 4;
-
-         else
-            return;
-
-         for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
-         {
-            *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
-            *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
-         }
-      }
-      else if (row_info->bit_depth == 16)
-      {
-         png_bytep rp;
-         png_uint_32 i;
-
-         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
-            bytes_per_pixel = 6;
-
-         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
-            bytes_per_pixel = 8;
-
-         else
-            return;
-
-         for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
-         {
-            png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
-            png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
-            png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
-            png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
-            png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
-            *(rp    ) = (png_byte)((red >> 8) & 0xff);
-            *(rp + 1) = (png_byte)(red & 0xff);
-            *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
-            *(rp + 5) = (png_byte)(blue & 0xff);
-         }
-      }
-   }
-}
-#endif /* PNG_MNG_FEATURES_SUPPORTED */
-#endif /* PNG_READ_SUPPORTED */