libwebp-0.6.0-rc1

third_party/libwebp/enc/near_lossless.c

-// Copyright 2014 Google Inc. All Rights Reserved.
-//
-// Use of this source code is governed by a BSD-style license
-// that can be found in the COPYING file in the root of the source
-// tree. An additional intellectual property rights grant can be found
-// in the file PATENTS. All contributing project authors may
-// be found in the AUTHORS file in the root of the source tree.
-// -----------------------------------------------------------------------------
-//
-// Near-lossless image preprocessing adjusts pixel values to help
-// compressibility with a guarantee of maximum deviation between original and
-// resulting pixel values.
-//
-// Author: Jyrki Alakuijala (jyrki@google.com)
-// Converted to C by Aleksander Kramarz (akramarz@google.com)
-
-#include <assert.h>
-#include <stdlib.h>
-
-#include "../dsp/lossless.h"
-#include "../utils/utils.h"
-#include "./vp8enci.h"
-
-#define MIN_DIM_FOR_NEAR_LOSSLESS 64
-#define MAX_LIMIT_BITS             5
-
-// Quantizes the value up or down to a multiple of 1<<bits (or to 255),
-// choosing the closer one, resolving ties using bankers' rounding.
-static int FindClosestDiscretized(int a, int bits) {
-  const int mask = (1 << bits) - 1;
-  const int biased = a + (mask >> 1) + ((a >> bits) & 1);
-  assert(bits > 0);
-  if (biased > 0xff) return 0xff;
-  return biased & ~mask;
-}
-
-// Applies FindClosestDiscretized to all channels of pixel.
-static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) {
-  return
-      (FindClosestDiscretized(a >> 24, bits) << 24) |
-      (FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) |
-      (FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) |
-      (FindClosestDiscretized(a & 0xff, bits));
-}
-
-// Checks if distance between corresponding channel values of pixels a and b
-// is within the given limit.
-static int IsNear(uint32_t a, uint32_t b, int limit) {
-  int k;
-  for (k = 0; k < 4; ++k) {
-    const int delta =
-        (int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff);
-    if (delta >= limit || delta <= -limit) {
-      return 0;
-    }
-  }
-  return 1;
-}
-
-static int IsSmooth(const uint32_t* const prev_row,
-                    const uint32_t* const curr_row,
-                    const uint32_t* const next_row,
-                    int ix, int limit) {
-  // Check that all pixels in 4-connected neighborhood are smooth.
-  return (IsNear(curr_row[ix], curr_row[ix - 1], limit) &&
-          IsNear(curr_row[ix], curr_row[ix + 1], limit) &&
-          IsNear(curr_row[ix], prev_row[ix], limit) &&
-          IsNear(curr_row[ix], next_row[ix], limit));
-}
-
-// Adjusts pixel values of image with given maximum error.
-static void NearLossless(int xsize, int ysize, uint32_t* argb,
-                         int limit_bits, uint32_t* copy_buffer) {
-  int x, y;
-  const int limit = 1 << limit_bits;
-  uint32_t* prev_row = copy_buffer;
-  uint32_t* curr_row = prev_row + xsize;
-  uint32_t* next_row = curr_row + xsize;
-  memcpy(copy_buffer, argb, xsize * 2 * sizeof(argb[0]));
-
-  for (y = 1; y < ysize - 1; ++y) {
-    uint32_t* const curr_argb_row = argb + y * xsize;
-    uint32_t* const next_argb_row = curr_argb_row + xsize;
-    memcpy(next_row, next_argb_row, xsize * sizeof(argb[0]));
-    for (x = 1; x < xsize - 1; ++x) {
-      if (!IsSmooth(prev_row, curr_row, next_row, x, limit)) {
-        curr_argb_row[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits);
-      }
-    }
-    {
-      // Three-way swap.
-      uint32_t* const temp = prev_row;
-      prev_row = curr_row;
-      curr_row = next_row;
-      next_row = temp;
-    }
-  }
-}
-
-int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
-  int i;
-  uint32_t* const copy_buffer =
-      (uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer));
-  const int limit_bits = VP8LNearLosslessBits(quality);
-  assert(argb != NULL);
-  assert(limit_bits >= 0);
-  assert(limit_bits <= MAX_LIMIT_BITS);
-  if (copy_buffer == NULL) {
-    return 0;
-  }
-  // For small icon images, don't attempt to apply near-lossless compression.
-  if (xsize < MIN_DIM_FOR_NEAR_LOSSLESS && ysize < MIN_DIM_FOR_NEAR_LOSSLESS) {
-    WebPSafeFree(copy_buffer);
-    return 1;
-  }
-
-  for (i = limit_bits; i != 0; --i) {
-    NearLossless(xsize, ysize, argb, i, copy_buffer);
-  }
-  WebPSafeFree(copy_buffer);
-  return 1;
-}