libwebp: update to 0.5.0

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 <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
+
+// Computes quantized pixel value and distance from original value.
+static void GetValAndDistance(int a, int initial, int bits,
+                              int* const val, int* const distance) {
+  const int mask = ~((1 << bits) - 1);
+  *val = (initial & mask) | (initial >> (8 - bits));
+  *distance = 2 * abs(a - *val);
+}
+
+// Clamps the value to range [0, 255].
+static int Clamp8b(int val) {
+  const int min_val = 0;
+  const int max_val = 0xff;
+  return (val < min_val) ? min_val : (val > max_val) ? max_val : val;
+}
+
+// Quantizes values {a, a+(1<<bits), a-(1<<bits)} and returns the nearest one.
+static int FindClosestDiscretized(int a, int bits) {
+  int best_val = a, i;
+  int min_distance = 256;
+
+  for (i = -1; i <= 1; ++i) {
+    int candidate, distance;
+    const int val = Clamp8b(a + i * (1 << bits));
+    GetValAndDistance(a, val, bits, &candidate, &distance);
+    if (i != 0) {
+      ++distance;
+    }
+    // Smallest distance but favor i == 0 over i == -1 and i == 1
+    // since that keeps the overall intensity more constant in the
+    // images.
+    if (distance < min_distance) {
+      min_distance = distance;
+      best_val = candidate;
+    }
+  }
+  return best_val;
+}
+
+// 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;
+    }
+  }
+}
+
+static int QualityToLimitBits(int quality) {
+  // quality mapping:
+  //  0..19 -> 5
+  //  0..39 -> 4
+  //  0..59 -> 3
+  //  0..79 -> 2
+  //  0..99 -> 1
+  //  100   -> 0
+  return MAX_LIMIT_BITS - quality / 20;
+}
+
+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 = QualityToLimitBits(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;
+}