third_party/libwebp/enc/alpha.c

   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@gmail.com)
  13
  14 #include <assert.h>
  15 #include <stdlib.h>
  16
  17 #include "./vp8enci.h"
  18 #include "../utils/filters.h"
  19 #include "../utils/quant_levels.h"
  20 #include "../webp/format_constants.h"
  21
  22 // -----------------------------------------------------------------------------
  23 // Encodes the given alpha data via specified compression method 'method'.
  24 // The pre-processing (quantization) is performed if 'quality' is less than 100.
  25 // For such cases, the encoding is lossy. The valid range is [0, 100] for
  26 // 'quality' and [0, 1] for 'method':
  27 //   'method = 0' - No compression;
  28 //   'method = 1' - Use lossless coder on the alpha plane only
  29 // 'filter' values [0, 4] correspond to prediction modes none, horizontal,
  30 // vertical & gradient filters. The prediction mode 4 will try all the
  31 // prediction modes 0 to 3 and pick the best one.
  32 // 'effort_level': specifies how much effort must be spent to try and reduce
  33 //  the compressed output size. In range 0 (quick) to 6 (slow).
  34 //
  35 // 'output' corresponds to the buffer containing compressed alpha data.
  36 //          This buffer is allocated by this method and caller should call
  37 //          free(*output) when done.
  38 // 'output_size' corresponds to size of this compressed alpha buffer.
  39 //
  40 // Returns 1 on successfully encoding the alpha and
  41 //         0 if either:
  42 //           invalid quality or method, or
  43 //           memory allocation for the compressed data fails.
  44
  45 #include "../enc/vp8li.h"
  46
  47 static int EncodeLossless(const uint8_t* const data, int width, int height,
  48                           int effort_level,  // in [0..6] range
  49                           VP8BitWriter* const bw,
  50                           WebPAuxStats* const stats) {
  51   int ok = 0;
  52   WebPConfig config;
  53   WebPPicture picture;
  54   VP8LBitWriter tmp_bw;
  55
  56   WebPPictureInit(&picture);
  57   picture.width = width;
  58   picture.height = height;
  59   picture.use_argb = 1;
  60   picture.stats = stats;
  61   if (!WebPPictureAlloc(&picture)) return 0;
  62
  63   // Transfer the alpha values to the green channel.
  64   {
  65     int i, j;
  66     uint32_t* dst = picture.argb;
  67     const uint8_t* src = data;
  68     for (j = 0; j < picture.height; ++j) {
  69       for (i = 0; i < picture.width; ++i) {
  70         dst[i] = src[i] << 8;  // we leave A/R/B channels zero'd.
  71       }
  72       src += width;
  73       dst += picture.argb_stride;
  74     }
  75   }
  76
  77   WebPConfigInit(&config);
  78   config.lossless = 1;
  79   config.method = effort_level;  // impact is very small
  80   // Set a low default quality for encoding alpha. Ensure that Alpha quality at
  81   // lower methods (3 and below) is less than the threshold for triggering
  82   // costly 'BackwardReferencesTraceBackwards'.
  83   config.quality = 8.f * effort_level;
  84   assert(config.quality >= 0 && config.quality <= 100.f);
  85
  86   ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);
  87   ok = ok && (VP8LEncodeStream(&config, &picture, &tmp_bw) == VP8_ENC_OK);
  88   WebPPictureFree(&picture);
  89   if (ok) {
  90     const uint8_t* const buffer = VP8LBitWriterFinish(&tmp_bw);
  91     const size_t buffer_size = VP8LBitWriterNumBytes(&tmp_bw);
  92     VP8BitWriterAppend(bw, buffer, buffer_size);
  93   }
  94   VP8LBitWriterDestroy(&tmp_bw);
  95   return ok && !bw->error_;
  96 }
  97
  98 // -----------------------------------------------------------------------------
  99
 100 // Small struct to hold the result of a filter mode compression attempt.
 101 typedef struct {
 102   size_t score;
 103   VP8BitWriter bw;
 104   WebPAuxStats stats;
 105 } FilterTrial;
 106
 107 // This function always returns an initialized 'bw' object, even upon error.
 108 static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
 109                                int method, int filter, int reduce_levels,
 110                                int effort_level,  // in [0..6] range
 111                                uint8_t* const tmp_alpha,
 112                                FilterTrial* result) {
 113   int ok = 0;
 114   const uint8_t* alpha_src;
 115   WebPFilterFunc filter_func;
 116   uint8_t header;
 117   size_t expected_size;
 118   const size_t data_size = width * height;
 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   // TODO(skal): have a common function and #define's to validate alpha params.
 126
 127   expected_size =
 128       (method == ALPHA_NO_COMPRESSION) ? (ALPHA_HEADER_LEN + data_size)
 129                                        : (data_size >> 5);
 130   header = method | (filter << 2);
 131   if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
 132
 133   VP8BitWriterInit(&result->bw, expected_size);
 134   VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN);
 135
 136   filter_func = WebPFilters[filter];
 137   if (filter_func != NULL) {
 138     filter_func(data, width, height, width, tmp_alpha);
 139     alpha_src = tmp_alpha;
 140   }  else {
 141     alpha_src = data;
 142   }
 143
 144   if (method == ALPHA_NO_COMPRESSION) {
 145     ok = VP8BitWriterAppend(&result->bw, alpha_src, width * height);
 146     ok = ok && !result->bw.error_;
 147   } else {
 148     ok = EncodeLossless(alpha_src, width, height, effort_level,
 149                         &result->bw, &result->stats);
 150     VP8BitWriterFinish(&result->bw);
 151   }
 152   result->score = VP8BitWriterSize(&result->bw);
 153   return ok;
 154 }
 155
 156 // -----------------------------------------------------------------------------
 157
 158 // TODO(skal): move to dsp/ ?
 159 static void CopyPlane(const uint8_t* src, int src_stride,
 160                       uint8_t* dst, int dst_stride, int width, int height) {
 161   while (height-- > 0) {
 162     memcpy(dst, src, width);
 163     src += src_stride;
 164     dst += dst_stride;
 165   }
 166 }
 167
 168 static int GetNumColors(const uint8_t* data, int width, int height,
 169                         int stride) {
 170   int j;
 171   int colors = 0;
 172   uint8_t color[256] = { 0 };
 173
 174   for (j = 0; j < height; ++j) {
 175     int i;
 176     const uint8_t* const p = data + j * stride;
 177     for (i = 0; i < width; ++i) {
 178       color[p[i]] = 1;
 179     }
 180   }
 181   for (j = 0; j < 256; ++j) {
 182     if (color[j] > 0) ++colors;
 183   }
 184   return colors;
 185 }
 186
 187 #define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE)
 188 #define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1)
 189
 190 // Given the input 'filter' option, return an OR'd bit-set of filters to try.
 191 static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height,
 192                              int filter, int effort_level) {
 193   uint32_t bit_map = 0U;
 194   if (filter == WEBP_FILTER_FAST) {
 195     // Quick estimate of the best candidate.
 196     int try_filter_none = (effort_level > 3);
 197     const int kMinColorsForFilterNone = 16;
 198     const int kMaxColorsForFilterNone = 192;
 199     const int num_colors = GetNumColors(alpha, width, height, width);
 200     // For low number of colors, NONE yields better compression.
 201     filter = (num_colors <= kMinColorsForFilterNone) ? WEBP_FILTER_NONE :
 202              EstimateBestFilter(alpha, width, height, width);
 203     bit_map |= 1 << filter;
 204     // For large number of colors, try FILTER_NONE in addition to the best
 205     // filter as well.
 206     if (try_filter_none || num_colors > kMaxColorsForFilterNone) {
 207       bit_map |= FILTER_TRY_NONE;
 208     }
 209   } else if (filter == WEBP_FILTER_NONE) {
 210     bit_map = FILTER_TRY_NONE;
 211   } else {  // WEBP_FILTER_BEST -> try all
 212     bit_map = FILTER_TRY_ALL;
 213   }
 214   return bit_map;
 215 }
 216
 217 static void InitFilterTrial(FilterTrial* const score) {
 218   score->score = (size_t)~0U;
 219   VP8BitWriterInit(&score->bw, 0);
 220 }
 221
 222 static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height,
 223                                  size_t data_size, int method, int filter,
 224                                  int reduce_levels, int effort_level,
 225                                  uint8_t** const output,
 226                                  size_t* const output_size,
 227                                  WebPAuxStats* const stats) {
 228   int ok = 1;
 229   FilterTrial best;
 230   uint32_t try_map =
 231       GetFilterMap(alpha, width, height, filter, effort_level);
 232   InitFilterTrial(&best);
 233   if (try_map != FILTER_TRY_NONE) {
 234     uint8_t* filtered_alpha =  (uint8_t*)malloc(data_size);
 235     if (filtered_alpha == NULL) return 0;
 236
 237     for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) {
 238       if (try_map & 1) {
 239         FilterTrial trial;
 240         ok = EncodeAlphaInternal(alpha, width, height, method, filter,
 241                                  reduce_levels, effort_level, filtered_alpha,
 242                                  &trial);
 243         if (ok && trial.score < best.score) {
 244           VP8BitWriterWipeOut(&best.bw);
 245           best = trial;
 246         } else {
 247           VP8BitWriterWipeOut(&trial.bw);
 248         }
 249       }
 250     }
 251     free(filtered_alpha);
 252   } else {
 253     ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE,
 254                              reduce_levels, effort_level, NULL, &best);
 255   }
 256   if (ok) {
 257     if (stats != NULL) *stats = best.stats;
 258     *output_size = VP8BitWriterSize(&best.bw);
 259     *output = VP8BitWriterBuf(&best.bw);
 260   } else {
 261     VP8BitWriterWipeOut(&best.bw);
 262   }
 263   return ok;
 264 }
 265
 266 static int EncodeAlpha(VP8Encoder* const enc,
 267                        int quality, int method, int filter,
 268                        int effort_level,
 269                        uint8_t** const output, size_t* const output_size) {
 270   const WebPPicture* const pic = enc->pic_;
 271   const int width = pic->width;
 272   const int height = pic->height;
 273
 274   uint8_t* quant_alpha = NULL;
 275   const size_t data_size = width * height;
 276   uint64_t sse = 0;
 277   int ok = 1;
 278   const int reduce_levels = (quality < 100);
 279
 280   // quick sanity checks
 281   assert((uint64_t)data_size == (uint64_t)width * height);  // as per spec
 282   assert(enc != NULL && pic != NULL && pic->a != NULL);
 283   assert(output != NULL && output_size != NULL);
 284   assert(width > 0 && height > 0);
 285   assert(pic->a_stride >= width);
 286   assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST);
 287
 288   if (quality < 0 || quality > 100) {
 289     return 0;
 290   }
 291
 292   if (method < ALPHA_NO_COMPRESSION || method > ALPHA_LOSSLESS_COMPRESSION) {
 293     return 0;
 294   }
 295
 296   if (method == ALPHA_NO_COMPRESSION) {
 297     // Don't filter, as filtering will make no impact on compressed size.
 298     filter = WEBP_FILTER_NONE;
 299   }
 300
 301   quant_alpha = (uint8_t*)malloc(data_size);
 302   if (quant_alpha == NULL) {
 303     return 0;
 304   }
 305
 306   // Extract alpha data (width x height) from raw_data (stride x height).
 307   CopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height);
 308
 309   if (reduce_levels) {  // No Quantization required for 'quality = 100'.
 310     // 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence
 311     // mapped to moderate quality 70. Hence Quality:[0, 70] -> Levels:[2, 16]
 312     // and Quality:]70, 100] -> Levels:]16, 256].
 313     const int alpha_levels = (quality <= 70) ? (2 + quality / 5)
 314                                              : (16 + (quality - 70) * 8);
 315     ok = QuantizeLevels(quant_alpha, width, height, alpha_levels, &sse);
 316   }
 317
 318   if (ok) {
 319     ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method,
 320                                filter, reduce_levels, effort_level, output,
 321                                output_size, pic->stats);
 322     if (pic->stats != NULL) {  // need stats?
 323       pic->stats->coded_size += (int)(*output_size);
 324       enc->sse_[3] = sse;
 325     }
 326   }
 327
 328   free(quant_alpha);
 329   return ok;
 330 }
 331
 332 //------------------------------------------------------------------------------
 333 // Main calls
 334
 335 static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) {
 336   const WebPConfig* config = enc->config_;
 337   uint8_t* alpha_data = NULL;
 338   size_t alpha_size = 0;
 339   const int effort_level = config->method;  // maps to [0..6]
 340   const WEBP_FILTER_TYPE filter =
 341       (config->alpha_filtering == 0) ? WEBP_FILTER_NONE :
 342       (config->alpha_filtering == 1) ? WEBP_FILTER_FAST :
 343                                        WEBP_FILTER_BEST;
 344   if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression,
 345                    filter, effort_level, &alpha_data, &alpha_size)) {
 346     return 0;
 347   }
 348   if (alpha_size != (uint32_t)alpha_size) {  // Sanity check.
 349     free(alpha_data);
 350     return 0;
 351   }
 352   enc->alpha_data_size_ = (uint32_t)alpha_size;
 353   enc->alpha_data_ = alpha_data;
 354   (void)dummy;
 355   return 1;
 356 }
 357
 358 void VP8EncInitAlpha(VP8Encoder* const enc) {
 359   enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_);
 360   enc->alpha_data_ = NULL;
 361   enc->alpha_data_size_ = 0;
 362   if (enc->thread_level_ > 0) {
 363     WebPWorker* const worker = &enc->alpha_worker_;
 364     WebPWorkerInit(worker);
 365     worker->data1 = enc;
 366     worker->data2 = NULL;
 367     worker->hook = (WebPWorkerHook)CompressAlphaJob;
 368   }
 369 }
 370
 371 int VP8EncStartAlpha(VP8Encoder* const enc) {
 372   if (enc->has_alpha_) {
 373     if (enc->thread_level_ > 0) {
 374       WebPWorker* const worker = &enc->alpha_worker_;
 375       if (!WebPWorkerReset(worker)) {    // Makes sure worker is good to go.
 376         return 0;
 377       }
 378       WebPWorkerLaunch(worker);
 379       return 1;
 380     } else {
 381       return CompressAlphaJob(enc, NULL);   // just do the job right away
 382     }
 383   }
 384   return 1;
 385 }
 386
 387 int VP8EncFinishAlpha(VP8Encoder* const enc) {
 388   if (enc->has_alpha_) {
 389     if (enc->thread_level_ > 0) {
 390       WebPWorker* const worker = &enc->alpha_worker_;
 391       if (!WebPWorkerSync(worker)) return 0;  // error
 392     }
 393   }
 394   return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
 395 }
 396
 397 int VP8EncDeleteAlpha(VP8Encoder* const enc) {
 398   int ok = 1;
 399   if (enc->thread_level_ > 0) {
 400     WebPWorker* const worker = &enc->alpha_worker_;
 401     ok = WebPWorkerSync(worker);  // finish anything left in flight
 402     WebPWorkerEnd(worker);  // still need to end the worker, even if !ok
 403   }
 404   free(enc->alpha_data_);
 405   enc->alpha_data_ = NULL;
 406   enc->alpha_data_size_ = 0;
 407   enc->has_alpha_ = 0;
 408   return ok;
 409 }
 410