1// Copyright 2013 Google Inc. All Rights Reserved. 2// 3// Use of this source code is governed by a BSD-style license 4// that can be found in the COPYING file in the root of the source 5// tree. An additional intellectual property rights grant can be found 6// in the file PATENTS. All contributing project authors may 7// be found in the AUTHORS file in the root of the source tree. 8// ----------------------------------------------------------------------------- 9// 10// Implement gradient smoothing: we replace a current alpha value by its 11// surrounding average if it's close enough (that is: the change will be less 12// than the minimum distance between two quantized level). 13// We use sliding window for computing the 2d moving average. 14// 15// Author: Skal (pascal.massimino@gmail.com) 16 17#include "./quant_levels_dec.h" 18 19#include <string.h> // for memset 20 21#include "./utils.h" 22 23// #define USE_DITHERING // uncomment to enable ordered dithering (not vital) 24 25#define FIX 16 // fix-point precision for averaging 26#define LFIX 2 // extra precision for look-up table 27#define LUT_SIZE ((1 << (8 + LFIX)) - 1) // look-up table size 28 29#if defined(USE_DITHERING) 30 31#define DFIX 4 // extra precision for ordered dithering 32#define DSIZE 4 // dithering size (must be a power of two) 33// cf. http://en.wikipedia.org/wiki/Ordered_dithering 34static const uint8_t kOrderedDither[DSIZE][DSIZE] = { 35 { 0, 8, 2, 10 }, // coefficients are in DFIX fixed-point precision 36 { 12, 4, 14, 6 }, 37 { 3, 11, 1, 9 }, 38 { 15, 7, 13, 5 } 39}; 40 41#else 42#define DFIX 0 43#endif 44 45typedef struct { 46 int width_, height_; // dimension 47 int row_; // current input row being processed 48 uint8_t* src_; // input pointer 49 uint8_t* dst_; // output pointer 50 51 int radius_; // filter radius (=delay) 52 int scale_; // normalization factor, in FIX bits precision 53 54 void* mem_; // all memory 55 56 // various scratch buffers 57 uint16_t* start_; 58 uint16_t* cur_; 59 uint16_t* end_; 60 uint16_t* top_; 61 uint16_t* average_; 62 63 // input levels distribution 64 int num_levels_; // number of quantized levels 65 int min_, max_; // min and max level values 66 int min_level_dist_; // smallest distance between two consecutive levels 67 68 int16_t* correction_; // size = 1 + 2*LUT_SIZE -> ~4k memory 69} SmoothParams; 70 71//------------------------------------------------------------------------------ 72 73#define CLIP_MASK (int)(~0U << (8 + DFIX)) 74static WEBP_INLINE uint8_t clip_8b(int v) { 75 return (!(v & CLIP_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u; 76} 77 78// vertical accumulation 79static void VFilter(SmoothParams* const p) { 80 const uint8_t* src = p->src_; 81 const int w = p->width_; 82 uint16_t* const cur = p->cur_; 83 const uint16_t* const top = p->top_; 84 uint16_t* const out = p->end_; 85 uint16_t sum = 0; // all arithmetic is modulo 16bit 86 int x; 87 88 for (x = 0; x < w; ++x) { 89 uint16_t new_value; 90 sum += src[x]; 91 new_value = top[x] + sum; 92 out[x] = new_value - cur[x]; // vertical sum of 'r' pixels. 93 cur[x] = new_value; 94 } 95 // move input pointers one row down 96 p->top_ = p->cur_; 97 p->cur_ += w; 98 if (p->cur_ == p->end_) p->cur_ = p->start_; // roll-over 99 // We replicate edges, as it's somewhat easier as a boundary condition. 100 // That's why we don't update the 'src' pointer on top/bottom area: 101 if (p->row_ >= 0 && p->row_ < p->height_ - 1) { 102 p->src_ += p->width_; 103 } 104} 105 106// horizontal accumulation. We use mirror replication of missing pixels, as it's 107// a little easier to implement (surprisingly). 108static void HFilter(SmoothParams* const p) { 109 const uint16_t* const in = p->end_; 110 uint16_t* const out = p->average_; 111 const uint32_t scale = p->scale_; 112 const int w = p->width_; 113 const int r = p->radius_; 114 115 int x; 116 for (x = 0; x <= r; ++x) { // left mirroring 117 const uint16_t delta = in[x + r - 1] + in[r - x]; 118 out[x] = (delta * scale) >> FIX; 119 } 120 for (; x < w - r; ++x) { // bulk middle run 121 const uint16_t delta = in[x + r] - in[x - r - 1]; 122 out[x] = (delta * scale) >> FIX; 123 } 124 for (; x < w; ++x) { // right mirroring 125 const uint16_t delta = 126 2 * in[w - 1] - in[2 * w - 2 - r - x] - in[x - r - 1]; 127 out[x] = (delta * scale) >> FIX; 128 } 129} 130 131// emit one filtered output row 132static void ApplyFilter(SmoothParams* const p) { 133 const uint16_t* const average = p->average_; 134 const int w = p->width_; 135 const int16_t* const correction = p->correction_; 136#if defined(USE_DITHERING) 137 const uint8_t* const dither = kOrderedDither[p->row_ % DSIZE]; 138#endif 139 uint8_t* const dst = p->dst_; 140 int x; 141 for (x = 0; x < w; ++x) { 142 const int v = dst[x]; 143 if (v < p->max_ && v > p->min_) { 144 const int c = (v << DFIX) + correction[average[x] - (v << LFIX)]; 145#if defined(USE_DITHERING) 146 dst[x] = clip_8b(c + dither[x % DSIZE]); 147#else 148 dst[x] = clip_8b(c); 149#endif 150 } 151 } 152 p->dst_ += w; // advance output pointer 153} 154 155//------------------------------------------------------------------------------ 156// Initialize correction table 157 158static void InitCorrectionLUT(int16_t* const lut, int min_dist) { 159 // The correction curve is: 160 // f(x) = x for x <= threshold2 161 // f(x) = 0 for x >= threshold1 162 // and a linear interpolation for range x=[threshold2, threshold1] 163 // (along with f(-x) = -f(x) symmetry). 164 // Note that: threshold2 = 3/4 * threshold1 165 const int threshold1 = min_dist << LFIX; 166 const int threshold2 = (3 * threshold1) >> 2; 167 const int max_threshold = threshold2 << DFIX; 168 const int delta = threshold1 - threshold2; 169 int i; 170 for (i = 1; i <= LUT_SIZE; ++i) { 171 int c = (i <= threshold2) ? (i << DFIX) 172 : (i < threshold1) ? max_threshold * (threshold1 - i) / delta 173 : 0; 174 c >>= LFIX; 175 lut[+i] = +c; 176 lut[-i] = -c; 177 } 178 lut[0] = 0; 179} 180 181static void CountLevels(const uint8_t* const data, int size, 182 SmoothParams* const p) { 183 int i, last_level; 184 uint8_t used_levels[256] = { 0 }; 185 p->min_ = 255; 186 p->max_ = 0; 187 for (i = 0; i < size; ++i) { 188 const int v = data[i]; 189 if (v < p->min_) p->min_ = v; 190 if (v > p->max_) p->max_ = v; 191 used_levels[v] = 1; 192 } 193 // Compute the mininum distance between two non-zero levels. 194 p->min_level_dist_ = p->max_ - p->min_; 195 last_level = -1; 196 for (i = 0; i < 256; ++i) { 197 if (used_levels[i]) { 198 ++p->num_levels_; 199 if (last_level >= 0) { 200 const int level_dist = i - last_level; 201 if (level_dist < p->min_level_dist_) { 202 p->min_level_dist_ = level_dist; 203 } 204 } 205 last_level = i; 206 } 207 } 208} 209 210// Initialize all params. 211static int InitParams(uint8_t* const data, int width, int height, 212 int radius, SmoothParams* const p) { 213 const int R = 2 * radius + 1; // total size of the kernel 214 215 const size_t size_scratch_m = (R + 1) * width * sizeof(*p->start_); 216 const size_t size_m = width * sizeof(*p->average_); 217 const size_t size_lut = (1 + 2 * LUT_SIZE) * sizeof(*p->correction_); 218 const size_t total_size = size_scratch_m + size_m + size_lut; 219 uint8_t* mem = (uint8_t*)WebPSafeMalloc(1U, total_size); 220 221 if (mem == NULL) return 0; 222 p->mem_ = (void*)mem; 223 224 p->start_ = (uint16_t*)mem; 225 p->cur_ = p->start_; 226 p->end_ = p->start_ + R * width; 227 p->top_ = p->end_ - width; 228 memset(p->top_, 0, width * sizeof(*p->top_)); 229 mem += size_scratch_m; 230 231 p->average_ = (uint16_t*)mem; 232 mem += size_m; 233 234 p->width_ = width; 235 p->height_ = height; 236 p->src_ = data; 237 p->dst_ = data; 238 p->radius_ = radius; 239 p->scale_ = (1 << (FIX + LFIX)) / (R * R); // normalization constant 240 p->row_ = -radius; 241 242 // analyze the input distribution so we can best-fit the threshold 243 CountLevels(data, width * height, p); 244 245 // correction table 246 p->correction_ = ((int16_t*)mem) + LUT_SIZE; 247 InitCorrectionLUT(p->correction_, p->min_level_dist_); 248 249 return 1; 250} 251 252static void CleanupParams(SmoothParams* const p) { 253 WebPSafeFree(p->mem_); 254} 255 256int WebPDequantizeLevels(uint8_t* const data, int width, int height, 257 int strength) { 258 const int radius = 4 * strength / 100; 259 if (strength < 0 || strength > 100) return 0; 260 if (data == NULL || width <= 0 || height <= 0) return 0; // bad params 261 if (radius > 0) { 262 SmoothParams p; 263 memset(&p, 0, sizeof(p)); 264 if (!InitParams(data, width, height, radius, &p)) return 0; 265 if (p.num_levels_ > 2) { 266 for (; p.row_ < p.height_; ++p.row_) { 267 VFilter(&p); // accumulate average of input 268 // Need to wait few rows in order to prime the filter, 269 // before emitting some output. 270 if (p.row_ >= p.radius_) { 271 HFilter(&p); 272 ApplyFilter(&p); 273 } 274 } 275 } 276 CleanupParams(&p); 277 } 278 return 1; 279} 280