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 "./vp8i_enc.h" 18 #include "../dsp/dsp.h" 19 #include "../utils/filters_utils.h" 20 #include "../utils/quant_levels_utils.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_enc.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 // TODO(urvang): Temporary fix to avoid generating images that trigger 83 // a decoder bug related to alpha with color cache. 84 // See: https://code.google.com/p/webp/issues/detail?id=239 85 // Need to re-enable this later. 86 ok = (VP8LEncodeStream(&config, &picture, bw, 0 /*use_cache*/) == VP8_ENC_OK); 87 WebPPictureFree(&picture); 88 ok = ok && !bw->error_; 89 if (!ok) { 90 VP8LBitWriterWipeOut(bw); 91 return 0; 92 } 93 return 1; 94 } 95 96 // ----------------------------------------------------------------------------- 97 98 // Small struct to hold the result of a filter mode compression attempt. 99 typedef struct { 100 size_t score; 101 VP8BitWriter bw; 102 WebPAuxStats stats; 103 } FilterTrial; 104 105 // This function always returns an initialized 'bw' object, even upon error. 106 static int EncodeAlphaInternal(const uint8_t* const data, int width, int height, 107 int method, int filter, int reduce_levels, 108 int effort_level, // in [0..6] range 109 uint8_t* const tmp_alpha, 110 FilterTrial* result) { 111 int ok = 0; 112 const uint8_t* alpha_src; 113 WebPFilterFunc filter_func; 114 uint8_t header; 115 const size_t data_size = width * height; 116 const uint8_t* output = NULL; 117 size_t output_size = 0; 118 VP8LBitWriter tmp_bw; 119 120 assert((uint64_t)data_size == (uint64_t)width * height); // as per spec 121 assert(filter >= 0 && filter < WEBP_FILTER_LAST); 122 assert(method >= ALPHA_NO_COMPRESSION); 123 assert(method <= ALPHA_LOSSLESS_COMPRESSION); 124 assert(sizeof(header) == ALPHA_HEADER_LEN); 125 126 filter_func = WebPFilters[filter]; 127 if (filter_func != NULL) { 128 filter_func(data, width, height, width, tmp_alpha); 129 alpha_src = tmp_alpha; 130 } else { 131 alpha_src = data; 132 } 133 134 if (method != ALPHA_NO_COMPRESSION) { 135 ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3); 136 ok = ok && EncodeLossless(alpha_src, width, height, effort_level, 137 &tmp_bw, &result->stats); 138 if (ok) { 139 output = VP8LBitWriterFinish(&tmp_bw); 140 output_size = VP8LBitWriterNumBytes(&tmp_bw); 141 if (output_size > data_size) { 142 // compressed size is larger than source! Revert to uncompressed mode. 143 method = ALPHA_NO_COMPRESSION; 144 VP8LBitWriterWipeOut(&tmp_bw); 145 } 146 } else { 147 VP8LBitWriterWipeOut(&tmp_bw); 148 return 0; 149 } 150 } 151 152 if (method == ALPHA_NO_COMPRESSION) { 153 output = alpha_src; 154 output_size = data_size; 155 ok = 1; 156 } 157 158 // Emit final result. 159 header = method | (filter << 2); 160 if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4; 161 162 VP8BitWriterInit(&result->bw, ALPHA_HEADER_LEN + output_size); 163 ok = ok && VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN); 164 ok = ok && VP8BitWriterAppend(&result->bw, output, output_size); 165 166 if (method != ALPHA_NO_COMPRESSION) { 167 VP8LBitWriterWipeOut(&tmp_bw); 168 } 169 ok = ok && !result->bw.error_; 170 result->score = VP8BitWriterSize(&result->bw); 171 return ok; 172 } 173 174 // ----------------------------------------------------------------------------- 175 176 static int GetNumColors(const uint8_t* data, int width, int height, 177 int stride) { 178 int j; 179 int colors = 0; 180 uint8_t color[256] = { 0 }; 181 182 for (j = 0; j < height; ++j) { 183 int i; 184 const uint8_t* const p = data + j * stride; 185 for (i = 0; i < width; ++i) { 186 color[p[i]] = 1; 187 } 188 } 189 for (j = 0; j < 256; ++j) { 190 if (color[j] > 0) ++colors; 191 } 192 return colors; 193 } 194 195 #define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE) 196 #define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1) 197 198 // Given the input 'filter' option, return an OR'd bit-set of filters to try. 199 static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height, 200 int filter, int effort_level) { 201 uint32_t bit_map = 0U; 202 if (filter == WEBP_FILTER_FAST) { 203 // Quick estimate of the best candidate. 204 int try_filter_none = (effort_level > 3); 205 const int kMinColorsForFilterNone = 16; 206 const int kMaxColorsForFilterNone = 192; 207 const int num_colors = GetNumColors(alpha, width, height, width); 208 // For low number of colors, NONE yields better compression. 209 filter = (num_colors <= kMinColorsForFilterNone) 210 ? WEBP_FILTER_NONE 211 : WebPEstimateBestFilter(alpha, width, height, width); 212 bit_map |= 1 << filter; 213 // For large number of colors, try FILTER_NONE in addition to the best 214 // filter as well. 215 if (try_filter_none || num_colors > kMaxColorsForFilterNone) { 216 bit_map |= FILTER_TRY_NONE; 217 } 218 } else if (filter == WEBP_FILTER_NONE) { 219 bit_map = FILTER_TRY_NONE; 220 } else { // WEBP_FILTER_BEST -> try all 221 bit_map = FILTER_TRY_ALL; 222 } 223 return bit_map; 224 } 225 226 static void InitFilterTrial(FilterTrial* const score) { 227 score->score = (size_t)~0U; 228 VP8BitWriterInit(&score->bw, 0); 229 } 230 231 static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height, 232 size_t data_size, int method, int filter, 233 int reduce_levels, int effort_level, 234 uint8_t** const output, 235 size_t* const output_size, 236 WebPAuxStats* const stats) { 237 int ok = 1; 238 FilterTrial best; 239 uint32_t try_map = 240 GetFilterMap(alpha, width, height, filter, effort_level); 241 InitFilterTrial(&best); 242 243 if (try_map != FILTER_TRY_NONE) { 244 uint8_t* filtered_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size); 245 if (filtered_alpha == NULL) return 0; 246 247 for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) { 248 if (try_map & 1) { 249 FilterTrial trial; 250 ok = EncodeAlphaInternal(alpha, width, height, method, filter, 251 reduce_levels, effort_level, filtered_alpha, 252 &trial); 253 if (ok && trial.score < best.score) { 254 VP8BitWriterWipeOut(&best.bw); 255 best = trial; 256 } else { 257 VP8BitWriterWipeOut(&trial.bw); 258 } 259 } 260 } 261 WebPSafeFree(filtered_alpha); 262 } else { 263 ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE, 264 reduce_levels, effort_level, NULL, &best); 265 } 266 if (ok) { 267 if (stats != NULL) { 268 stats->lossless_features = best.stats.lossless_features; 269 stats->histogram_bits = best.stats.histogram_bits; 270 stats->transform_bits = best.stats.transform_bits; 271 stats->cache_bits = best.stats.cache_bits; 272 stats->palette_size = best.stats.palette_size; 273 stats->lossless_size = best.stats.lossless_size; 274 stats->lossless_hdr_size = best.stats.lossless_hdr_size; 275 stats->lossless_data_size = best.stats.lossless_data_size; 276 } 277 *output_size = VP8BitWriterSize(&best.bw); 278 *output = VP8BitWriterBuf(&best.bw); 279 } else { 280 VP8BitWriterWipeOut(&best.bw); 281 } 282 return ok; 283 } 284 285 static int EncodeAlpha(VP8Encoder* const enc, 286 int quality, int method, int filter, 287 int effort_level, 288 uint8_t** const output, size_t* const output_size) { 289 const WebPPicture* const pic = enc->pic_; 290 const int width = pic->width; 291 const int height = pic->height; 292 293 uint8_t* quant_alpha = NULL; 294 const size_t data_size = width * height; 295 uint64_t sse = 0; 296 int ok = 1; 297 const int reduce_levels = (quality < 100); 298 299 // quick sanity checks 300 assert((uint64_t)data_size == (uint64_t)width * height); // as per spec 301 assert(enc != NULL && pic != NULL && pic->a != NULL); 302 assert(output != NULL && output_size != NULL); 303 assert(width > 0 && height > 0); 304 assert(pic->a_stride >= width); 305 assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST); 306 307 if (quality < 0 || quality > 100) { 308 return 0; 309 } 310 311 if (method < ALPHA_NO_COMPRESSION || method > ALPHA_LOSSLESS_COMPRESSION) { 312 return 0; 313 } 314 315 if (method == ALPHA_NO_COMPRESSION) { 316 // Don't filter, as filtering will make no impact on compressed size. 317 filter = WEBP_FILTER_NONE; 318 } 319 320 quant_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size); 321 if (quant_alpha == NULL) { 322 return 0; 323 } 324 325 // Extract alpha data (width x height) from raw_data (stride x height). 326 WebPCopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height); 327 328 if (reduce_levels) { // No Quantization required for 'quality = 100'. 329 // 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence 330 // mapped to moderate quality 70. Hence Quality:[0, 70] -> Levels:[2, 16] 331 // and Quality:]70, 100] -> Levels:]16, 256]. 332 const int alpha_levels = (quality <= 70) ? (2 + quality / 5) 333 : (16 + (quality - 70) * 8); 334 ok = QuantizeLevels(quant_alpha, width, height, alpha_levels, &sse); 335 } 336 337 if (ok) { 338 VP8FiltersInit(); 339 ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method, 340 filter, reduce_levels, effort_level, output, 341 output_size, pic->stats); 342 if (pic->stats != NULL) { // need stats? 343 pic->stats->coded_size += (int)(*output_size); 344 enc->sse_[3] = sse; 345 } 346 } 347 348 WebPSafeFree(quant_alpha); 349 return ok; 350 } 351 352 //------------------------------------------------------------------------------ 353 // Main calls 354 355 static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) { 356 const WebPConfig* config = enc->config_; 357 uint8_t* alpha_data = NULL; 358 size_t alpha_size = 0; 359 const int effort_level = config->method; // maps to [0..6] 360 const WEBP_FILTER_TYPE filter = 361 (config->alpha_filtering == 0) ? WEBP_FILTER_NONE : 362 (config->alpha_filtering == 1) ? WEBP_FILTER_FAST : 363 WEBP_FILTER_BEST; 364 if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression, 365 filter, effort_level, &alpha_data, &alpha_size)) { 366 return 0; 367 } 368 if (alpha_size != (uint32_t)alpha_size) { // Sanity check. 369 WebPSafeFree(alpha_data); 370 return 0; 371 } 372 enc->alpha_data_size_ = (uint32_t)alpha_size; 373 enc->alpha_data_ = alpha_data; 374 (void)dummy; 375 return 1; 376 } 377 378 void VP8EncInitAlpha(VP8Encoder* const enc) { 379 WebPInitAlphaProcessing(); 380 enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_); 381 enc->alpha_data_ = NULL; 382 enc->alpha_data_size_ = 0; 383 if (enc->thread_level_ > 0) { 384 WebPWorker* const worker = &enc->alpha_worker_; 385 WebPGetWorkerInterface()->Init(worker); 386 worker->data1 = enc; 387 worker->data2 = NULL; 388 worker->hook = (WebPWorkerHook)CompressAlphaJob; 389 } 390 } 391 392 int VP8EncStartAlpha(VP8Encoder* const enc) { 393 if (enc->has_alpha_) { 394 if (enc->thread_level_ > 0) { 395 WebPWorker* const worker = &enc->alpha_worker_; 396 // Makes sure worker is good to go. 397 if (!WebPGetWorkerInterface()->Reset(worker)) { 398 return 0; 399 } 400 WebPGetWorkerInterface()->Launch(worker); 401 return 1; 402 } else { 403 return CompressAlphaJob(enc, NULL); // just do the job right away 404 } 405 } 406 return 1; 407 } 408 409 int VP8EncFinishAlpha(VP8Encoder* const enc) { 410 if (enc->has_alpha_) { 411 if (enc->thread_level_ > 0) { 412 WebPWorker* const worker = &enc->alpha_worker_; 413 if (!WebPGetWorkerInterface()->Sync(worker)) return 0; // error 414 } 415 } 416 return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_); 417 } 418 419 int VP8EncDeleteAlpha(VP8Encoder* const enc) { 420 int ok = 1; 421 if (enc->thread_level_ > 0) { 422 WebPWorker* const worker = &enc->alpha_worker_; 423 // finish anything left in flight 424 ok = WebPGetWorkerInterface()->Sync(worker); 425 // still need to end the worker, even if !ok 426 WebPGetWorkerInterface()->End(worker); 427 } 428 WebPSafeFree(enc->alpha_data_); 429 enc->alpha_data_ = NULL; 430 enc->alpha_data_size_ = 0; 431 enc->has_alpha_ = 0; 432 return ok; 433 } 434
