Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/utils/quant_levels_dec.c

+// Copyright 2013 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.
+// -----------------------------------------------------------------------------
+//
+// Implement gradient smoothing: we replace a current alpha value by its
+// surrounding average if it's close enough (that is: the change will be less
+// than the minimum distance between two quantized level).
+// We use sliding window for computing the 2d moving average.
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include "./quant_levels_dec.h"
+
+#include <string.h>   // for memset
+
+#include "./utils.h"
+
+// #define USE_DITHERING   // uncomment to enable ordered dithering (not vital)
+
+#define FIX 16     // fix-point precision for averaging
+#define LFIX 2     // extra precision for look-up table
+#define LUT_SIZE ((1 << (8 + LFIX)) - 1)  // look-up table size
+
+#if defined(USE_DITHERING)
+
+#define DFIX 4           // extra precision for ordered dithering
+#define DSIZE 4          // dithering size (must be a power of two)
+// cf. http://en.wikipedia.org/wiki/Ordered_dithering
+static const uint8_t kOrderedDither[DSIZE][DSIZE] = {
+  {  0,  8,  2, 10 },     // coefficients are in DFIX fixed-point precision
+  { 12,  4, 14,  6 },
+  {  3, 11,  1,  9 },
+  { 15,  7, 13,  5 }
+};
+
+#else
+#define DFIX 0
+#endif
+
+typedef struct {
+  int width_, height_;  // dimension
+  int row_;             // current input row being processed
+  uint8_t* src_;        // input pointer
+  uint8_t* dst_;        // output pointer
+
+  int radius_;          // filter radius (=delay)
+  int scale_;           // normalization factor, in FIX bits precision
+
+  void* mem_;           // all memory
+
+  // various scratch buffers
+  uint16_t* start_;
+  uint16_t* cur_;
+  uint16_t* end_;
+  uint16_t* top_;
+  uint16_t* average_;
+
+  // input levels distribution
+  int num_levels_;       // number of quantized levels
+  int min_, max_;        // min and max level values
+  int min_level_dist_;   // smallest distance between two consecutive levels
+
+  int16_t* correction_;  // size = 1 + 2*LUT_SIZE  -> ~4k memory
+} SmoothParams;
+
+//------------------------------------------------------------------------------
+
+#define CLIP_MASK (int)(~0U << (8 + DFIX))
+static WEBP_INLINE uint8_t clip_8b(int v) {
+  return (!(v & CLIP_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u;
+}
+
+// vertical accumulation
+static void VFilter(SmoothParams* const p) {
+  const uint8_t* src = p->src_;
+  const int w = p->width_;
+  uint16_t* const cur = p->cur_;
+  const uint16_t* const top = p->top_;
+  uint16_t* const out = p->end_;
+  uint16_t sum = 0;               // all arithmetic is modulo 16bit
+  int x;
+
+  for (x = 0; x < w; ++x) {
+    uint16_t new_value;
+    sum += src[x];
+    new_value = top[x] + sum;
+    out[x] = new_value - cur[x];  // vertical sum of 'r' pixels.
+    cur[x] = new_value;
+  }
+  // move input pointers one row down
+  p->top_ = p->cur_;
+  p->cur_ += w;
+  if (p->cur_ == p->end_) p->cur_ = p->start_;  // roll-over
+  // We replicate edges, as it's somewhat easier as a boundary condition.
+  // That's why we don't update the 'src' pointer on top/bottom area:
+  if (p->row_ >= 0 && p->row_ < p->height_ - 1) {
+    p->src_ += p->width_;
+  }
+}
+
+// horizontal accumulation. We use mirror replication of missing pixels, as it's
+// a little easier to implement (surprisingly).
+static void HFilter(SmoothParams* const p) {
+  const uint16_t* const in = p->end_;
+  uint16_t* const out = p->average_;
+  const uint32_t scale = p->scale_;
+  const int w = p->width_;
+  const int r = p->radius_;
+
+  int x;
+  for (x = 0; x <= r; ++x) {   // left mirroring
+    const uint16_t delta = in[x + r - 1] + in[r - x];
+    out[x] = (delta * scale) >> FIX;
+  }
+  for (; x < w - r; ++x) {     // bulk middle run
+    const uint16_t delta = in[x + r] - in[x - r - 1];
+    out[x] = (delta * scale) >> FIX;
+  }
+  for (; x < w; ++x) {         // right mirroring
+    const uint16_t delta =
+        2 * in[w - 1] - in[2 * w - 2 - r - x] - in[x - r - 1];
+    out[x] = (delta * scale) >> FIX;
+  }
+}
+
+// emit one filtered output row
+static void ApplyFilter(SmoothParams* const p) {
+  const uint16_t* const average = p->average_;
+  const int w = p->width_;
+  const int16_t* const correction = p->correction_;
+#if defined(USE_DITHERING)
+  const uint8_t* const dither = kOrderedDither[p->row_ % DSIZE];
+#endif
+  uint8_t* const dst = p->dst_;
+  int x;
+  for (x = 0; x < w; ++x) {
+    const int v = dst[x];
+    if (v < p->max_ && v > p->min_) {
+      const int c = (v << DFIX) + correction[average[x] - (v << LFIX)];
+#if defined(USE_DITHERING)
+      dst[x] = clip_8b(c + dither[x % DSIZE]);
+#else
+      dst[x] = clip_8b(c);
+#endif
+    }
+  }
+  p->dst_ += w;  // advance output pointer
+}
+
+//------------------------------------------------------------------------------
+// Initialize correction table
+
+static void InitCorrectionLUT(int16_t* const lut, int min_dist) {
+  // The correction curve is:
+  //   f(x) = x for x <= threshold2
+  //   f(x) = 0 for x >= threshold1
+  // and a linear interpolation for range x=[threshold2, threshold1]
+  // (along with f(-x) = -f(x) symmetry).
+  // Note that: threshold2 = 3/4 * threshold1
+  const int threshold1 = min_dist << LFIX;
+  const int threshold2 = (3 * threshold1) >> 2;
+  const int max_threshold = threshold2 << DFIX;
+  const int delta = threshold1 - threshold2;
+  int i;
+  for (i = 1; i <= LUT_SIZE; ++i) {
+    int c = (i <= threshold2) ? (i << DFIX)
+          : (i < threshold1) ? max_threshold * (threshold1 - i) / delta
+          : 0;
+    c >>= LFIX;
+    lut[+i] = +c;
+    lut[-i] = -c;
+  }
+  lut[0] = 0;
+}
+
+static void CountLevels(const uint8_t* const data, int size,
+                        SmoothParams* const p) {
+  int i, last_level;
+  uint8_t used_levels[256] = { 0 };
+  p->min_ = 255;
+  p->max_ = 0;
+  for (i = 0; i < size; ++i) {
+    const int v = data[i];
+    if (v < p->min_) p->min_ = v;
+    if (v > p->max_) p->max_ = v;
+    used_levels[v] = 1;
+  }
+  // Compute the mininum distance between two non-zero levels.
+  p->min_level_dist_ = p->max_ - p->min_;
+  last_level = -1;
+  for (i = 0; i < 256; ++i) {
+    if (used_levels[i]) {
+      ++p->num_levels_;
+      if (last_level >= 0) {
+        const int level_dist = i - last_level;
+        if (level_dist < p->min_level_dist_) {
+          p->min_level_dist_ = level_dist;
+        }
+      }
+      last_level = i;
+    }
+  }
+}
+
+// Initialize all params.
+static int InitParams(uint8_t* const data, int width, int height,
+                      int radius, SmoothParams* const p) {
+  const int R = 2 * radius + 1;  // total size of the kernel
+
+  const size_t size_scratch_m = (R + 1) * width * sizeof(*p->start_);
+  const size_t size_m =  width * sizeof(*p->average_);
+  const size_t size_lut = (1 + 2 * LUT_SIZE) * sizeof(*p->correction_);
+  const size_t total_size = size_scratch_m + size_m + size_lut;
+  uint8_t* mem = (uint8_t*)WebPSafeMalloc(1U, total_size);
+
+  if (mem == NULL) return 0;
+  p->mem_ = (void*)mem;
+
+  p->start_ = (uint16_t*)mem;
+  p->cur_ = p->start_;
+  p->end_ = p->start_ + R * width;
+  p->top_ = p->end_ - width;
+  memset(p->top_, 0, width * sizeof(*p->top_));
+  mem += size_scratch_m;
+
+  p->average_ = (uint16_t*)mem;
+  mem += size_m;
+
+  p->width_ = width;
+  p->height_ = height;
+  p->src_ = data;
+  p->dst_ = data;
+  p->radius_ = radius;
+  p->scale_ = (1 << (FIX + LFIX)) / (R * R);  // normalization constant
+  p->row_ = -radius;
+
+  // analyze the input distribution so we can best-fit the threshold
+  CountLevels(data, width * height, p);
+
+  // correction table
+  p->correction_ = ((int16_t*)mem) + LUT_SIZE;
+  InitCorrectionLUT(p->correction_, p->min_level_dist_);
+
+  return 1;
+}
+
+static void CleanupParams(SmoothParams* const p) {
+  WebPSafeFree(p->mem_);
+}
+
+int WebPDequantizeLevels(uint8_t* const data, int width, int height,
+                         int strength) {
+  const int radius = 4 * strength / 100;
+  if (strength < 0 || strength > 100) return 0;
+  if (data == NULL || width <= 0 || height <= 0) return 0;  // bad params
+  if (radius > 0) {
+    SmoothParams p;
+    memset(&p, 0, sizeof(p));
+    if (!InitParams(data, width, height, radius, &p)) return 0;
+    if (p.num_levels_ > 2) {
+      for (; p.row_ < p.height_; ++p.row_) {
+        VFilter(&p);  // accumulate average of input
+        // Need to wait few rows in order to prime the filter,
+        // before emitting some output.
+        if (p.row_ >= p.radius_) {
+          HFilter(&p);
+          ApplyFilter(&p);
+        }
+      }
+    }
+    CleanupParams(&p);
+  }
+  return 1;
+}