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| 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 | |
| 34 static 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 | |
| 45 typedef struct { | |
| 46 int width_, height_; // dimension | |
| 47 int stride_; // stride in bytes | |
| 48 int row_; // current input row being processed | |
| 49 uint8_t* src_; // input pointer | |
| 50 uint8_t* dst_; // output pointer | |
| 51 | |
| 52 int radius_; // filter radius (=delay) | |
| 53 int scale_; // normalization factor, in FIX bits precision | |
| 54 | |
| 55 void* mem_; // all memory | |
| 56 | |
| 57 // various scratch buffers | |
| 58 uint16_t* start_; | |
| 59 uint16_t* cur_; | |
| 60 uint16_t* end_; | |
| 61 uint16_t* top_; | |
| 62 uint16_t* average_; | |
| 63 | |
| 64 // input levels distribution | |
| 65 int num_levels_; // number of quantized levels | |
| 66 int min_, max_; // min and max level values | |
| 67 int min_level_dist_; // smallest distance between two consecutive levels | |
| 68 | |
| 69 int16_t* correction_; // size = 1 + 2*LUT_SIZE -> ~4k memory | |
| 70 } SmoothParams; | |
| 71 | |
| 72 //------------------------------------------------------------------------------ | |
| 73 | |
| 74 #define CLIP_MASK (int)(~0U << (8 + DFIX)) | |
| 75 static WEBP_INLINE uint8_t clip_8b(int v) { | |
| 76 return (!(v & CLIP_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u; | |
| 77 } | |
| 78 | |
| 79 // vertical accumulation | |
| 80 static void VFilter(SmoothParams* const p) { | |
| 81 const uint8_t* src = p->src_; | |
| 82 const int w = p->width_; | |
| 83 uint16_t* const cur = p->cur_; | |
| 84 const uint16_t* const top = p->top_; | |
| 85 uint16_t* const out = p->end_; | |
| 86 uint16_t sum = 0; // all arithmetic is modulo 16bit | |
| 87 int x; | |
| 88 | |
| 89 for (x = 0; x < w; ++x) { | |
| 90 uint16_t new_value; | |
| 91 sum += src[x]; | |
| 92 new_value = top[x] + sum; | |
| 93 out[x] = new_value - cur[x]; // vertical sum of 'r' pixels. | |
| 94 cur[x] = new_value; | |
| 95 } | |
| 96 // move input pointers one row down | |
| 97 p->top_ = p->cur_; | |
| 98 p->cur_ += w; | |
| 99 if (p->cur_ == p->end_) p->cur_ = p->start_; // roll-over | |
| 100 // We replicate edges, as it's somewhat easier as a boundary condition. | |
| 101 // That's why we don't update the 'src' pointer on top/bottom area: | |
| 102 if (p->row_ >= 0 && p->row_ < p->height_ - 1) { | |
| 103 p->src_ += p->stride_; | |
| 104 } | |
| 105 } | |
| 106 | |
| 107 // horizontal accumulation. We use mirror replication of missing pixels, as it's | |
| 108 // a little easier to implement (surprisingly). | |
| 109 static void HFilter(SmoothParams* const p) { | |
| 110 const uint16_t* const in = p->end_; | |
| 111 uint16_t* const out = p->average_; | |
| 112 const uint32_t scale = p->scale_; | |
| 113 const int w = p->width_; | |
| 114 const int r = p->radius_; | |
| 115 | |
| 116 int x; | |
| 117 for (x = 0; x <= r; ++x) { // left mirroring | |
| 118 const uint16_t delta = in[x + r - 1] + in[r - x]; | |
| 119 out[x] = (delta * scale) >> FIX; | |
| 120 } | |
| 121 for (; x < w - r; ++x) { // bulk middle run | |
| 122 const uint16_t delta = in[x + r] - in[x - r - 1]; | |
| 123 out[x] = (delta * scale) >> FIX; | |
| 124 } | |
| 125 for (; x < w; ++x) { // right mirroring | |
| 126 const uint16_t delta = | |
| 127 2 * in[w - 1] - in[2 * w - 2 - r - x] - in[x - r - 1]; | |
| 128 out[x] = (delta * scale) >> FIX; | |
| 129 } | |
| 130 } | |
| 131 | |
| 132 // emit one filtered output row | |
| 133 static void ApplyFilter(SmoothParams* const p) { | |
| 134 const uint16_t* const average = p->average_; | |
| 135 const int w = p->width_; | |
| 136 const int16_t* const correction = p->correction_; | |
| 137 #if defined(USE_DITHERING) | |
| 138 const uint8_t* const dither = kOrderedDither[p->row_ % DSIZE]; | |
| 139 #endif | |
| 140 uint8_t* const dst = p->dst_; | |
| 141 int x; | |
| 142 for (x = 0; x < w; ++x) { | |
| 143 const int v = dst[x]; | |
| 144 if (v < p->max_ && v > p->min_) { | |
| 145 const int c = (v << DFIX) + correction[average[x] - (v << LFIX)]; | |
| 146 #if defined(USE_DITHERING) | |
| 147 dst[x] = clip_8b(c + dither[x % DSIZE]); | |
| 148 #else | |
| 149 dst[x] = clip_8b(c); | |
| 150 #endif | |
| 151 } | |
| 152 } | |
| 153 p->dst_ += p->stride_; // advance output pointer | |
| 154 } | |
| 155 | |
| 156 //------------------------------------------------------------------------------ | |
| 157 // Initialize correction table | |
| 158 | |
| 159 static void InitCorrectionLUT(int16_t* const lut, int min_dist) { | |
| 160 // The correction curve is: | |
| 161 // f(x) = x for x <= threshold2 | |
| 162 // f(x) = 0 for x >= threshold1 | |
| 163 // and a linear interpolation for range x=[threshold2, threshold1] | |
| 164 // (along with f(-x) = -f(x) symmetry). | |
| 165 // Note that: threshold2 = 3/4 * threshold1 | |
| 166 const int threshold1 = min_dist << LFIX; | |
| 167 const int threshold2 = (3 * threshold1) >> 2; | |
| 168 const int max_threshold = threshold2 << DFIX; | |
| 169 const int delta = threshold1 - threshold2; | |
| 170 int i; | |
| 171 for (i = 1; i <= LUT_SIZE; ++i) { | |
| 172 int c = (i <= threshold2) ? (i << DFIX) | |
| 173 : (i < threshold1) ? max_threshold * (threshold1 - i) / delta | |
| 174 : 0; | |
| 175 c >>= LFIX; | |
| 176 lut[+i] = +c; | |
| 177 lut[-i] = -c; | |
| 178 } | |
| 179 lut[0] = 0; | |
| 180 } | |
| 181 | |
| 182 static void CountLevels(SmoothParams* const p) { | |
| 183 int i, j, last_level; | |
| 184 uint8_t used_levels[256] = { 0 }; | |
| 185 const uint8_t* data = p->src_; | |
| 186 p->min_ = 255; | |
| 187 p->max_ = 0; | |
| 188 for (j = 0; j < p->height_; ++j) { | |
| 189 for (i = 0; i < p->width_; ++i) { | |
| 190 const int v = data[i]; | |
| 191 if (v < p->min_) p->min_ = v; | |
| 192 if (v > p->max_) p->max_ = v; | |
| 193 used_levels[v] = 1; | |
| 194 } | |
| 195 data += p->stride_; | |
| 196 } | |
| 197 // Compute the mininum distance between two non-zero levels. | |
| 198 p->min_level_dist_ = p->max_ - p->min_; | |
| 199 last_level = -1; | |
| 200 for (i = 0; i < 256; ++i) { | |
| 201 if (used_levels[i]) { | |
| 202 ++p->num_levels_; | |
| 203 if (last_level >= 0) { | |
| 204 const int level_dist = i - last_level; | |
| 205 if (level_dist < p->min_level_dist_) { | |
| 206 p->min_level_dist_ = level_dist; | |
| 207 } | |
| 208 } | |
| 209 last_level = i; | |
| 210 } | |
| 211 } | |
| 212 } | |
| 213 | |
| 214 // Initialize all params. | |
| 215 static int InitParams(uint8_t* const data, int width, int height, int stride, | |
| 216 int radius, SmoothParams* const p) { | |
| 217 const int R = 2 * radius + 1; // total size of the kernel | |
| 218 | |
| 219 const size_t size_scratch_m = (R + 1) * width * sizeof(*p->start_); | |
| 220 const size_t size_m = width * sizeof(*p->average_); | |
| 221 const size_t size_lut = (1 + 2 * LUT_SIZE) * sizeof(*p->correction_); | |
| 222 const size_t total_size = size_scratch_m + size_m + size_lut; | |
| 223 uint8_t* mem = (uint8_t*)WebPSafeMalloc(1U, total_size); | |
| 224 | |
| 225 if (mem == NULL) return 0; | |
| 226 p->mem_ = (void*)mem; | |
| 227 | |
| 228 p->start_ = (uint16_t*)mem; | |
| 229 p->cur_ = p->start_; | |
| 230 p->end_ = p->start_ + R * width; | |
| 231 p->top_ = p->end_ - width; | |
| 232 memset(p->top_, 0, width * sizeof(*p->top_)); | |
| 233 mem += size_scratch_m; | |
| 234 | |
| 235 p->average_ = (uint16_t*)mem; | |
| 236 mem += size_m; | |
| 237 | |
| 238 p->width_ = width; | |
| 239 p->height_ = height; | |
| 240 p->stride_ = stride; | |
| 241 p->src_ = data; | |
| 242 p->dst_ = data; | |
| 243 p->radius_ = radius; | |
| 244 p->scale_ = (1 << (FIX + LFIX)) / (R * R); // normalization constant | |
| 245 p->row_ = -radius; | |
| 246 | |
| 247 // analyze the input distribution so we can best-fit the threshold | |
| 248 CountLevels(p); | |
| 249 | |
| 250 // correction table | |
| 251 p->correction_ = ((int16_t*)mem) + LUT_SIZE; | |
| 252 InitCorrectionLUT(p->correction_, p->min_level_dist_); | |
| 253 | |
| 254 return 1; | |
| 255 } | |
| 256 | |
| 257 static void CleanupParams(SmoothParams* const p) { | |
| 258 WebPSafeFree(p->mem_); | |
| 259 } | |
| 260 | |
| 261 int WebPDequantizeLevels(uint8_t* const data, int width, int height, int stride, | |
| 262 int strength) { | |
| 263 const int radius = 4 * strength / 100; | |
| 264 if (strength < 0 || strength > 100) return 0; | |
| 265 if (data == NULL || width <= 0 || height <= 0) return 0; // bad params | |
| 266 if (radius > 0) { | |
| 267 SmoothParams p; | |
| 268 memset(&p, 0, sizeof(p)); | |
| 269 if (!InitParams(data, width, height, stride, radius, &p)) return 0; | |
| 270 if (p.num_levels_ > 2) { | |
| 271 for (; p.row_ < p.height_; ++p.row_) { | |
| 272 VFilter(&p); // accumulate average of input | |
| 273 // Need to wait few rows in order to prime the filter, | |
| 274 // before emitting some output. | |
| 275 if (p.row_ >= p.radius_) { | |
| 276 HFilter(&p); | |
| 277 ApplyFilter(&p); | |
| 278 } | |
| 279 } | |
| 280 } | |
| 281 CleanupParams(&p); | |
| 282 } | |
| 283 return 1; | |
| 284 } | |
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Issue 2651883004:
libwebp-0.6.0-rc1 (Closed)
