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// Copyright 2011 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Alpha-plane compression.
//
// Author: Skal (pascal.massimino@gmail.com)
#include <assert.h>
#include <stdlib.h>
#include "src/enc/vp8i_enc.h"
#include "src/dsp/dsp.h"
#include "src/utils/filters_utils.h"
#include "src/utils/quant_levels_utils.h"
#include "src/utils/utils.h"
#include "src/webp/format_constants.h"
// -----------------------------------------------------------------------------
// Encodes the given alpha data via specified compression method 'method'.
// The pre-processing (quantization) is performed if 'quality' is less than 100.
// For such cases, the encoding is lossy. The valid range is [0, 100] for
// 'quality' and [0, 1] for 'method':
// 'method = 0' - No compression;
// 'method = 1' - Use lossless coder on the alpha plane only
// 'filter' values [0, 4] correspond to prediction modes none, horizontal,
// vertical & gradient filters. The prediction mode 4 will try all the
// prediction modes 0 to 3 and pick the best one.
// 'effort_level': specifies how much effort must be spent to try and reduce
// the compressed output size. In range 0 (quick) to 6 (slow).
//
// 'output' corresponds to the buffer containing compressed alpha data.
// This buffer is allocated by this method and caller should call
// WebPSafeFree(*output) when done.
// 'output_size' corresponds to size of this compressed alpha buffer.
//
// Returns 1 on successfully encoding the alpha and
// 0 if either:
// invalid quality or method, or
// memory allocation for the compressed data fails.
#include "src/enc/vp8li_enc.h"
static int EncodeLossless(const uint8_t* const data, int width, int height,
int effort_level, // in [0..6] range
int use_quality_100, VP8LBitWriter* const bw,
WebPAuxStats* const stats) {
int ok = 0;
WebPConfig config;
WebPPicture picture;
WebPPictureInit(&picture);
picture.width = width;
picture.height = height;
picture.use_argb = 1;
picture.stats = stats;
if (!WebPPictureAlloc(&picture)) return 0;
// Transfer the alpha values to the green channel.
WebPDispatchAlphaToGreen(data, width, picture.width, picture.height,
picture.argb, picture.argb_stride);
WebPConfigInit(&config);
config.lossless = 1;
// Enable exact, or it would alter RGB values of transparent alpha, which is
// normally OK but not here since we are not encoding the input image but an
// internal encoding-related image containing necessary exact information in
// RGB channels.
config.exact = 1;
config.method = effort_level; // impact is very small
// Set a low default quality for encoding alpha. Ensure that Alpha quality at
// lower methods (3 and below) is less than the threshold for triggering
// costly 'BackwardReferencesTraceBackwards'.
// If the alpha quality is set to 100 and the method to 6, allow for a high
// lossless quality to trigger the cruncher.
config.quality =
(use_quality_100 && effort_level == 6) ? 100 : 8.f * effort_level;
assert(config.quality >= 0 && config.quality <= 100.f);
// TODO(urvang): Temporary fix to avoid generating images that trigger
// a decoder bug related to alpha with color cache.
// See: https://code.google.com/p/webp/issues/detail?id=239
// Need to re-enable this later.
ok = (VP8LEncodeStream(&config, &picture, bw, 0 /*use_cache*/) == VP8_ENC_OK);
WebPPictureFree(&picture);
ok = ok && !bw->error_;
if (!ok) {
VP8LBitWriterWipeOut(bw);
return 0;
}
return 1;
}
// -----------------------------------------------------------------------------
// Small struct to hold the result of a filter mode compression attempt.
typedef struct {
size_t score;
VP8BitWriter bw;
WebPAuxStats stats;
} FilterTrial;
// This function always returns an initialized 'bw' object, even upon error.
static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
int method, int filter, int reduce_levels,
int effort_level, // in [0..6] range
uint8_t* const tmp_alpha,
FilterTrial* result) {
int ok = 0;
const uint8_t* alpha_src;
WebPFilterFunc filter_func;
uint8_t header;
const size_t data_size = width * height;
const uint8_t* output = NULL;
size_t output_size = 0;
VP8LBitWriter tmp_bw;
assert((uint64_t)data_size == (uint64_t)width * height); // as per spec
assert(filter >= 0 && filter < WEBP_FILTER_LAST);
assert(method >= ALPHA_NO_COMPRESSION);
assert(method <= ALPHA_LOSSLESS_COMPRESSION);
assert(sizeof(header) == ALPHA_HEADER_LEN);
filter_func = WebPFilters[filter];
if (filter_func != NULL) {
filter_func(data, width, height, width, tmp_alpha);
alpha_src = tmp_alpha;
} else {
alpha_src = data;
}
if (method != ALPHA_NO_COMPRESSION) {
ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3);
ok = ok && EncodeLossless(alpha_src, width, height, effort_level,
!reduce_levels, &tmp_bw, &result->stats);
if (ok) {
output = VP8LBitWriterFinish(&tmp_bw);
output_size = VP8LBitWriterNumBytes(&tmp_bw);
if (output_size > data_size) {
// compressed size is larger than source! Revert to uncompressed mode.
method = ALPHA_NO_COMPRESSION;
VP8LBitWriterWipeOut(&tmp_bw);
}
} else {
VP8LBitWriterWipeOut(&tmp_bw);
return 0;
}
}
if (method == ALPHA_NO_COMPRESSION) {
output = alpha_src;
output_size = data_size;
ok = 1;
}
// Emit final result.
header = method | (filter << 2);
if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
VP8BitWriterInit(&result->bw, ALPHA_HEADER_LEN + output_size);
ok = ok && VP8BitWriterAppend(&result->bw, &header, ALPHA_HEADER_LEN);
ok = ok && VP8BitWriterAppend(&result->bw, output, output_size);
if (method != ALPHA_NO_COMPRESSION) {
VP8LBitWriterWipeOut(&tmp_bw);
}
ok = ok && !result->bw.error_;
result->score = VP8BitWriterSize(&result->bw);
return ok;
}
// -----------------------------------------------------------------------------
static int GetNumColors(const uint8_t* data, int width, int height,
int stride) {
int j;
int colors = 0;
uint8_t color[256] = { 0 };
for (j = 0; j < height; ++j) {
int i;
const uint8_t* const p = data + j * stride;
for (i = 0; i < width; ++i) {
color[p[i]] = 1;
}
}
for (j = 0; j < 256; ++j) {
if (color[j] > 0) ++colors;
}
return colors;
}
#define FILTER_TRY_NONE (1 << WEBP_FILTER_NONE)
#define FILTER_TRY_ALL ((1 << WEBP_FILTER_LAST) - 1)
// Given the input 'filter' option, return an OR'd bit-set of filters to try.
static uint32_t GetFilterMap(const uint8_t* alpha, int width, int height,
int filter, int effort_level) {
uint32_t bit_map = 0U;
if (filter == WEBP_FILTER_FAST) {
// Quick estimate of the best candidate.
int try_filter_none = (effort_level > 3);
const int kMinColorsForFilterNone = 16;
const int kMaxColorsForFilterNone = 192;
const int num_colors = GetNumColors(alpha, width, height, width);
// For low number of colors, NONE yields better compression.
filter = (num_colors <= kMinColorsForFilterNone)
? WEBP_FILTER_NONE
: WebPEstimateBestFilter(alpha, width, height, width);
bit_map |= 1 << filter;
// For large number of colors, try FILTER_NONE in addition to the best
// filter as well.
if (try_filter_none || num_colors > kMaxColorsForFilterNone) {
bit_map |= FILTER_TRY_NONE;
}
} else if (filter == WEBP_FILTER_NONE) {
bit_map = FILTER_TRY_NONE;
} else { // WEBP_FILTER_BEST -> try all
bit_map = FILTER_TRY_ALL;
}
return bit_map;
}
static void InitFilterTrial(FilterTrial* const score) {
score->score = (size_t)~0U;
VP8BitWriterInit(&score->bw, 0);
}
static int ApplyFiltersAndEncode(const uint8_t* alpha, int width, int height,
size_t data_size, int method, int filter,
int reduce_levels, int effort_level,
uint8_t** const output,
size_t* const output_size,
WebPAuxStats* const stats) {
int ok = 1;
FilterTrial best;
uint32_t try_map =
GetFilterMap(alpha, width, height, filter, effort_level);
InitFilterTrial(&best);
if (try_map != FILTER_TRY_NONE) {
uint8_t* filtered_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size);
if (filtered_alpha == NULL) return 0;
for (filter = WEBP_FILTER_NONE; ok && try_map; ++filter, try_map >>= 1) {
if (try_map & 1) {
FilterTrial trial;
ok = EncodeAlphaInternal(alpha, width, height, method, filter,
reduce_levels, effort_level, filtered_alpha,
&trial);
if (ok && trial.score < best.score) {
VP8BitWriterWipeOut(&best.bw);
best = trial;
} else {
VP8BitWriterWipeOut(&trial.bw);
}
}
}
WebPSafeFree(filtered_alpha);
} else {
ok = EncodeAlphaInternal(alpha, width, height, method, WEBP_FILTER_NONE,
reduce_levels, effort_level, NULL, &best);
}
if (ok) {
#if !defined(WEBP_DISABLE_STATS)
if (stats != NULL) {
stats->lossless_features = best.stats.lossless_features;
stats->histogram_bits = best.stats.histogram_bits;
stats->transform_bits = best.stats.transform_bits;
stats->cache_bits = best.stats.cache_bits;
stats->palette_size = best.stats.palette_size;
stats->lossless_size = best.stats.lossless_size;
stats->lossless_hdr_size = best.stats.lossless_hdr_size;
stats->lossless_data_size = best.stats.lossless_data_size;
}
#else
(void)stats;
#endif
*output_size = VP8BitWriterSize(&best.bw);
*output = VP8BitWriterBuf(&best.bw);
} else {
VP8BitWriterWipeOut(&best.bw);
}
return ok;
}
static int EncodeAlpha(VP8Encoder* const enc,
int quality, int method, int filter,
int effort_level,
uint8_t** const output, size_t* const output_size) {
const WebPPicture* const pic = enc->pic_;
const int width = pic->width;
const int height = pic->height;
uint8_t* quant_alpha = NULL;
const size_t data_size = width * height;
uint64_t sse = 0;
int ok = 1;
const int reduce_levels = (quality < 100);
// quick correctness checks
assert((uint64_t)data_size == (uint64_t)width * height); // as per spec
assert(enc != NULL && pic != NULL && pic->a != NULL);
assert(output != NULL && output_size != NULL);
assert(width > 0 && height > 0);
assert(pic->a_stride >= width);
assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST);
if (quality < 0 || quality > 100) {
return 0;
}
if (method < ALPHA_NO_COMPRESSION || method > ALPHA_LOSSLESS_COMPRESSION) {
return 0;
}
if (method == ALPHA_NO_COMPRESSION) {
// Don't filter, as filtering will make no impact on compressed size.
filter = WEBP_FILTER_NONE;
}
quant_alpha = (uint8_t*)WebPSafeMalloc(1ULL, data_size);
if (quant_alpha == NULL) {
return 0;
}
// Extract alpha data (width x height) from raw_data (stride x height).
WebPCopyPlane(pic->a, pic->a_stride, quant_alpha, width, width, height);
if (reduce_levels) { // No Quantization required for 'quality = 100'.
// 16 alpha levels gives quite a low MSE w.r.t original alpha plane hence
// mapped to moderate quality 70. Hence Quality:[0, 70] -> Levels:[2, 16]
// and Quality:]70, 100] -> Levels:]16, 256].
const int alpha_levels = (quality <= 70) ? (2 + quality / 5)
: (16 + (quality - 70) * 8);
ok = QuantizeLevels(quant_alpha, width, height, alpha_levels, &sse);
}
if (ok) {
VP8FiltersInit();
ok = ApplyFiltersAndEncode(quant_alpha, width, height, data_size, method,
filter, reduce_levels, effort_level, output,
output_size, pic->stats);
#if !defined(WEBP_DISABLE_STATS)
if (pic->stats != NULL) { // need stats?
pic->stats->coded_size += (int)(*output_size);
enc->sse_[3] = sse;
}
#endif
}
WebPSafeFree(quant_alpha);
return ok;
}
//------------------------------------------------------------------------------
// Main calls
static int CompressAlphaJob(void* arg1, void* unused) {
VP8Encoder* const enc = (VP8Encoder*)arg1;
const WebPConfig* config = enc->config_;
uint8_t* alpha_data = NULL;
size_t alpha_size = 0;
const int effort_level = config->method; // maps to [0..6]
const WEBP_FILTER_TYPE filter =
(config->alpha_filtering == 0) ? WEBP_FILTER_NONE :
(config->alpha_filtering == 1) ? WEBP_FILTER_FAST :
WEBP_FILTER_BEST;
if (!EncodeAlpha(enc, config->alpha_quality, config->alpha_compression,
filter, effort_level, &alpha_data, &alpha_size)) {
return 0;
}
if (alpha_size != (uint32_t)alpha_size) { // Soundness check.
WebPSafeFree(alpha_data);
return 0;
}
enc->alpha_data_size_ = (uint32_t)alpha_size;
enc->alpha_data_ = alpha_data;
(void)unused;
return 1;
}
void VP8EncInitAlpha(VP8Encoder* const enc) {
WebPInitAlphaProcessing();
enc->has_alpha_ = WebPPictureHasTransparency(enc->pic_);
enc->alpha_data_ = NULL;
enc->alpha_data_size_ = 0;
if (enc->thread_level_ > 0) {
WebPWorker* const worker = &enc->alpha_worker_;
WebPGetWorkerInterface()->Init(worker);
worker->data1 = enc;
worker->data2 = NULL;
worker->hook = CompressAlphaJob;
}
}
int VP8EncStartAlpha(VP8Encoder* const enc) {
if (enc->has_alpha_) {
if (enc->thread_level_ > 0) {
WebPWorker* const worker = &enc->alpha_worker_;
// Makes sure worker is good to go.
if (!WebPGetWorkerInterface()->Reset(worker)) {
return 0;
}
WebPGetWorkerInterface()->Launch(worker);
return 1;
} else {
return CompressAlphaJob(enc, NULL); // just do the job right away
}
}
return 1;
}
int VP8EncFinishAlpha(VP8Encoder* const enc) {
if (enc->has_alpha_) {
if (enc->thread_level_ > 0) {
WebPWorker* const worker = &enc->alpha_worker_;
if (!WebPGetWorkerInterface()->Sync(worker)) return 0; // error
}
}
return WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
}
int VP8EncDeleteAlpha(VP8Encoder* const enc) {
int ok = 1;
if (enc->thread_level_ > 0) {
WebPWorker* const worker = &enc->alpha_worker_;
// finish anything left in flight
ok = WebPGetWorkerInterface()->Sync(worker);
// still need to end the worker, even if !ok
WebPGetWorkerInterface()->End(worker);
}
WebPSafeFree(enc->alpha_data_);
enc->alpha_data_ = NULL;
enc->alpha_data_size_ = 0;
enc->has_alpha_ = 0;
return ok;
}