1 // Copyright 2011 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 // Alpha-plane compression. 11 // 12 // Author: Skal (pascal.massimino (at) gmail.com) 13 14 #include <assert.h> 15 #include <stdlib.h> 16 17 #include "./vp8enci.h" 18 #include "../dsp/dsp.h" 19 #include "../utils/filters.h" 20 #include "../utils/quant_levels.h" 21 #include "../utils/utils.h" 22 #include "../webp/format_constants.h" 23 24 // ----------------------------------------------------------------------------- 25 // Encodes the given alpha data via specified compression method 'method'. 26 // The pre-processing (quantization) is performed if 'quality' is less than 100. 27 // For such cases, the encoding is lossy. The valid range is [0, 100] for 28 // 'quality' and [0, 1] for 'method': 29 // 'method = 0' - No compression; 30 // 'method = 1' - Use lossless coder on the alpha plane only 31 // 'filter' values [0, 4] correspond to prediction modes none, horizontal, 32 // vertical & gradient filters. The prediction mode 4 will try all the 33 // prediction modes 0 to 3 and pick the best one. 34 // 'effort_level': specifies how much effort must be spent to try and reduce 35 // the compressed output size. In range 0 (quick) to 6 (slow). 36 // 37 // 'output' corresponds to the buffer containing compressed alpha data. 38 // This buffer is allocated by this method and caller should call 39 // WebPSafeFree(*output) when done. 40 // 'output_size' corresponds to size of this compressed alpha buffer. 41 // 42 // Returns 1 on successfully encoding the alpha and 43 // 0 if either: 44 // invalid quality or method, or 45 // memory allocation for the compressed data fails. 46 47 #include "../enc/vp8li.h" 48 49 static int EncodeLossless(const uint8_t* const data, int width, int height, 50 int effort_level, // in [0..6] range 51 VP8LBitWriter* const bw, 52 WebPAuxStats* const stats) { 53 int ok = 0; 54 WebPConfig config; 55 WebPPicture picture; 56 57 WebPPictureInit(&picture); 58 picture.width = width; 59 picture.height = height; 60 picture.use_argb = 1; 61 picture.stats = stats; 62 if (!WebPPictureAlloc(&picture)) return 0; 63 64 // Transfer the alpha values to the green channel. 65 WebPDispatchAlphaToGreen(data, width, picture.width, picture.height, 66 picture.argb, picture.argb_stride); 67 68 WebPConfigInit(&config); 69 config.lossless = 1; 70 // Enable exact, or it would alter RGB values of transparent alpha, which is 71 // normally OK but not here since we are not encoding the input image but an 72 // internal encoding-related image containing necessary exact information in 73 // RGB channels. 74 config.exact = 1; 75 config.method = effort_level; // impact is very small 76 // Set a low default quality for encoding alpha. Ensure that Alpha quality at 77 // lower methods (3 and below) is less than the threshold for triggering 78 // costly 'BackwardReferencesTraceBackwards'. 79 config.quality = 8.f * effort_level; 80 assert(config.quality >= 0 && config.quality <= 100.f); 81 82 ok = (VP8LEncodeStream(&config, &picture, bw) == VP8_ENC_OK); 83 WebPPictureFree(&picture); 84 ok = ok && !bw->error_; 85 if (!ok) { 86 VP8LBitWriterWipeOut(bw); 87 return 0; 88 } 89 return 1; 90 } 91 92 // ----------------------------------------------------------------------------- 93 94 // Small struct to hold the result of a filter mode compression attempt. 95 typedef struct { 96 size_t score; 97 VP8BitWriter bw; 98 WebPAuxStats stats; 99 } FilterTrial; 100 101 // This function always returns an initialized 'bw' object, even upon error. 102 static int EncodeAlphaInternal(const uint8_t* const data, int width, int height, 103 int method, int filter, int reduce_levels, 104 int effort_level, // in [0..6] range 105 uint8_t* const tmp_alpha, 106 FilterTrial* result) { 107 int ok = 0; 108 const uint8_t* alpha_src; 109 WebPFilterFunc filter_func; 110 uint8_t header; 111 const size_t data_size = width * height; 112 const uint8_t* output = NULL; 113 size_t output_size = 0; 114 VP8LBitWriter tmp_bw; 115 116 assert((uint64_t)data_size == (uint64_t)width * height); // as per spec 117 assert(filter >= 0 && filter < WEBP_FILTER_LAST); 118 assert(method >= ALPHA_NO_COMPRESSION); 119 assert(method <= ALPHA_LOSSLESS_COMPRESSION); 120 assert(sizeof(header) == ALPHA_HEADER_LEN); 121 // TODO(skal): have a common function and #define's to validate alpha params. 122 123 filter_func = WebPFilters[filter]; 124 if (filter_func != NULL) { 125 filter_func(data, width, height, width, tmp_alpha); 126 alpha_src = tmp_alpha; 127 } else { 128 alpha_src = data; 129 } 130 131 if (method != ALPHA_NO_COMPRESSION) { 132 ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3); 133 ok = ok && EncodeLossless(alpha_src, width, height, effort_level, 134 &tmp_bw, &result->stats); 135 if (ok) { 136 output = VP8LBitWriterFinish(&tmp_bw); 137 output_size = VP8LBitWriterNumBytes(&tmp_bw); 138 if (output_size > data_size) { 139 // compressed size is larger than source! Revert to uncompressed mode. 140 method = ALPHA_NO_COMPRESSION; 141 VP8LBitWriterWipeOut(&tmp_bw); 142 } 143 } else { 144 VP8LBitWriterWipeOut(&tmp_bw); 145 return 0; 146 } 147 } 148 149 if (method == ALPHA_NO_COMPRESSION) { 150 output = alpha_src; 151 output_size = data_size; 152 ok = 1; 153 } 154 155 // Emit final result. 156 header = method | (filter << 2); 157 if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4; 158 159 VP8BitWriterInit(&result->bw, ALPHA_HEADER_LEN + output_size); 160 ok = ok && VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN); 161 ok = ok && VP8BitWriterAppend(&result->bw, output, output_size); 162 163 if (method != ALPHA_NO_COMPRESSION) { 164 VP8LBitWriterWipeOut(&tmp_bw); 165 } 166 ok = ok && !result->bw.error_; 167 result->score = VP8BitWriterSize(&result->bw); 168 return ok; 169 } 170 171 // ----------------------------------------------------------------------------- 172 173 static int GetNumColors(const uint8_t* data, int width, int height, 174 int stride) { 175 int j; 176 int colors = 0; 177 uint8_t color[256] = { 0 }; 178 179 for (j = 0; j < height; ++j) { 180 int i; 181 const uint8_t* const p = data + j * stride; 182 for (i = 0; i < width; ++i) { 183 color[p[i]] = 1; 184 } 185 } 186 for (j = 0; j < 256; ++j) { 187 if (color[j] > 0) ++colors; 188 } 189 return colors; 190 } 191 192 #define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE) 193 #define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1) 194 195 // Given the input 'filter' option, return an OR'd bit-set of filters to try. 196 static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height, 197 int filter, int effort_level) { 198 uint32_t bit_map = 0U; 199 if (filter == WEBP_FILTER_FAST) { 200 // Quick estimate of the best candidate. 201 int try_filter_none = (effort_level > 3); 202 const int kMinColorsForFilterNone = 16; 203 const int kMaxColorsForFilterNone = 192; 204 const int num_colors = GetNumColors(alpha, width, height, width); 205 // For low number of colors, NONE yields better compression. 206 filter = (num_colors <= kMinColorsForFilterNone) 207 ? WEBP_FILTER_NONE 208 : WebPEstimateBestFilter(alpha, width, height, width); 209 bit_map |= 1 << filter; 210 // For large number of colors, try FILTER_NONE in addition to the best 211 // filter as well. 212 if (try_filter_none || num_colors > kMaxColorsForFilterNone) { 213 bit_map |= FILTER_TRY_NONE; 214 } 215 } else if (filter == WEBP_FILTER_NONE) { 216 bit_map = FILTER_TRY_NONE; 217 } else { // WEBP_FILTER_BEST -> try all 218 bit_map = FILTER_TRY_ALL; 219 } 220 return bit_map; 221 } 222 223 static void InitFilterTrial(FilterTrial* const score) { 224 score->score = (size_t)~0U; 225 VP8BitWriterInit(&score->bw, 0); 226 } 227 228 static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height, 229 size_t data_size, int method, int filter, 230 int reduce_levels, int effort_level, 231 uint8_t** const output, 232 size_t* const output_size, 233 WebPAuxStats* const stats) { 234 int ok = 1; 235 FilterTrial best; 236 uint32_t try_map = 237 GetFilterMap(alpha, width, height, filter, effort_level); 238 InitFilterTrial(&best); 239 240 if (try_map != FILTER_TRY_NONE) { 241 uint8_t* filtered_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size); 242 if (filtered_alpha == NULL) return 0; 243 244 for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) { 245 if (try_map & 1) { 246 FilterTrial trial; 247 ok = EncodeAlphaInternal(alpha, width, height, method, filter, 248 reduce_levels, effort_level, filtered_alpha, 249 &trial); 250 if (ok && trial.score < best.score) { 251 VP8BitWriterWipeOut(&best.bw); 252 best = trial; 253 } else { 254 VP8BitWriterWipeOut(&trial.bw); 255 } 256 } 257 } 258 WebPSafeFree(filtered_alpha); 259 } else { 260 ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE, 261 reduce_levels, effort_level, NULL, &best); 262 } 263 if (ok) { 264 if (stats != NULL) { 265 stats->lossless_features = best.stats.lossless_features; 266 stats->histogram_bits = best.stats.histogram_bits; 267 stats->transform_bits = best.stats.transform_bits; 268 stats->cache_bits = best.stats.cache_bits; 269 stats->palette_size = best.stats.palette_size; 270 stats->lossless_size = best.stats.lossless_size; 271 stats->lossless_hdr_size = best.stats.lossless_hdr_size; 272 stats->lossless_data_size = best.stats.lossless_data_size; 273 } 274 *output_size = VP8BitWriterSize(&best.bw); 275 *output = VP8BitWriterBuf(&best.bw); 276 } else { 277 VP8BitWriterWipeOut(&best.bw); 278 } 279 return ok; 280 } 281 282 static int EncodeAlpha(VP8Encoder* const enc, 283 int quality, int method, int filter, 284 int effort_level, 285 uint8_t** const output, size_t* const output_size) { 286 const WebPPicture* const pic = enc->pic_; 287 const int width = pic->width; 288 const int height = pic->height; 289 290 uint8_t* quant_alpha = NULL; 291 const size_t data_size = width * height; 292 uint64_t sse = 0; 293 int ok = 1; 294 const int reduce_levels = (quality < 100); 295 296 // quick sanity checks 297 assert((uint64_t)data_size == (uint64_t)width * height); // as per spec 298 assert(enc != NULL && pic != NULL && pic->a != NULL); 299 assert(output != NULL && output_size != NULL); 300 assert(width > 0 && height > 0); 301 assert(pic->a_stride >= width); 302 assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST); 303 304 if (quality < 0 || quality > 100) { 305 return 0; 306 } 307 308 if (method < ALPHA_NO_COMPRESSION || method > ALPHA_LOSSLESS_COMPRESSION) { 309 return 0; 310 } 311 312 if (method == ALPHA_NO_COMPRESSION) { 313 // Don't filter, as filtering will make no impact on compressed size. 314 filter = WEBP_FILTER_NONE; 315 } 316 317 quant_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size); 318 if (quant_alpha == NULL) { 319 return 0; 320 } 321 322 // Extract alpha data (width x height) from raw_data (stride x height). 323 WebPCopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height); 324 325 if (reduce_levels) { // No Quantization required for 'quality = 100'. 326 // 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence 327 // mapped to moderate quality 70. Hence Quality:[0, 70] -> Levels:[2, 16] 328 // and Quality:]70, 100] -> Levels:]16, 256]. 329 const int alpha_levels = (quality <= 70) ? (2 + quality / 5) 330 : (16 + (quality - 70) * 8); 331 ok = QuantizeLevels(quant_alpha, width, height, alpha_levels, &sse); 332 } 333 334 if (ok) { 335 VP8FiltersInit(); 336 ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method, 337 filter, reduce_levels, effort_level, output, 338 output_size, pic->stats); 339 if (pic->stats != NULL) { // need stats? 340 pic->stats->coded_size += (int)(*output_size); 341 enc->sse_[3] = sse; 342 } 343 } 344 345 WebPSafeFree(quant_alpha); 346 return ok; 347 } 348 349 //------------------------------------------------------------------------------ 350 // Main calls 351 352 static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) { 353 const WebPConfig* config = enc->config_; 354 uint8_t* alpha_data = NULL; 355 size_t alpha_size = 0; 356 const int effort_level = config->method; // maps to [0..6] 357 const WEBP_FILTER_TYPE filter = 358 (config->alpha_filtering == 0) ? WEBP_FILTER_NONE : 359 (config->alpha_filtering == 1) ? WEBP_FILTER_FAST : 360 WEBP_FILTER_BEST; 361 if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression, 362 filter, effort_level, &alpha_data, &alpha_size)) { 363 return 0; 364 } 365 if (alpha_size != (uint32_t)alpha_size) { // Sanity check. 366 WebPSafeFree(alpha_data); 367 return 0; 368 } 369 enc->alpha_data_size_ = (uint32_t)alpha_size; 370 enc->alpha_data_ = alpha_data; 371 (void)dummy; 372 return 1; 373 } 374 375 void VP8EncInitAlpha(VP8Encoder* const enc) { 376 WebPInitAlphaProcessing(); 377 enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_); 378 enc->alpha_data_ = NULL; 379 enc->alpha_data_size_ = 0; 380 if (enc->thread_level_ > 0) { 381 WebPWorker* const worker = &enc->alpha_worker_; 382 WebPGetWorkerInterface()->Init(worker); 383 worker->data1 = enc; 384 worker->data2 = NULL; 385 worker->hook = (WebPWorkerHook)CompressAlphaJob; 386 } 387 } 388 389 int VP8EncStartAlpha(VP8Encoder* const enc) { 390 if (enc->has_alpha_) { 391 if (enc->thread_level_ > 0) { 392 WebPWorker* const worker = &enc->alpha_worker_; 393 // Makes sure worker is good to go. 394 if (!WebPGetWorkerInterface()->Reset(worker)) { 395 return 0; 396 } 397 WebPGetWorkerInterface()->Launch(worker); 398 return 1; 399 } else { 400 return CompressAlphaJob(enc, NULL); // just do the job right away 401 } 402 } 403 return 1; 404 } 405 406 int VP8EncFinishAlpha(VP8Encoder* const enc) { 407 if (enc->has_alpha_) { 408 if (enc->thread_level_ > 0) { 409 WebPWorker* const worker = &enc->alpha_worker_; 410 if (!WebPGetWorkerInterface()->Sync(worker)) return 0; // error 411 } 412 } 413 return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_); 414 } 415 416 int VP8EncDeleteAlpha(VP8Encoder* const enc) { 417 int ok = 1; 418 if (enc->thread_level_ > 0) { 419 WebPWorker* const worker = &enc->alpha_worker_; 420 // finish anything left in flight 421 ok = WebPGetWorkerInterface()->Sync(worker); 422 // still need to end the worker, even if !ok 423 WebPGetWorkerInterface()->End(worker); 424 } 425 WebPSafeFree(enc->alpha_data_); 426 enc->alpha_data_ = NULL; 427 enc->alpha_data_size_ = 0; 428 enc->has_alpha_ = 0; 429 return ok; 430 } 431
