third_party/libwebp/utils/quant_levels_dec.c - chromium/src - Git at Google

 // 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;
 }
	// 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;
	}