// 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 "./vp8enci.h"
#include "../utils/filters.h"
#include "../utils/quant_levels.h"
#include "../webp/format_constants.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// -----------------------------------------------------------------------------
// 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
// free(*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 "../enc/vp8li.h"
static int EncodeLossless(const uint8_t* const data, int width, int height,
int effort_level, // in [0..6] range
VP8BitWriter* const bw,
WebPAuxStats* const stats) {
int ok = 0;
WebPConfig config;
WebPPicture picture;
VP8LBitWriter tmp_bw;
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.
{
int i, j;
uint32_t* dst = picture.argb;
const uint8_t* src = data;
for (j = 0; j < picture.height; ++j) {
for (i = 0; i < picture.width; ++i) {
dst[i] = (src[i] << 8) | 0xff000000u;
}
src += width;
dst += picture.argb_stride;
}
}
WebPConfigInit(&config);
config.lossless = 1;
config.method = effort_level; // impact is very small
// Set a moderate default quality setting for alpha.
config.quality = 10.f * effort_level;
assert(config.quality >= 0 && config.quality <= 100.f);
ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);
ok = ok && (VP8LEncodeStream(&config, &picture, &tmp_bw) == VP8_ENC_OK);
WebPPictureFree(&picture);
if (ok) {
const uint8_t* const buffer = VP8LBitWriterFinish(&tmp_bw);
const size_t buffer_size = VP8LBitWriterNumBytes(&tmp_bw);
VP8BitWriterAppend(bw, buffer, buffer_size);
}
VP8LBitWriterDestroy(&tmp_bw);
return ok && !bw->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,
VP8BitWriter* const bw,
WebPAuxStats* const stats) {
int ok = 0;
const uint8_t* alpha_src;
WebPFilterFunc filter_func;
uint8_t header;
size_t expected_size;
const size_t data_size = width * height;
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);
// TODO(skal): have a common function and #define's to validate alpha params.
expected_size =
(method == ALPHA_NO_COMPRESSION) ? (ALPHA_HEADER_LEN + data_size)
: (data_size >> 5);
header = method | (filter << 2);
if (reduce_levels) header |= ALPHA_PREPROCESSED_LEVELS << 4;
VP8BitWriterInit(bw, expected_size);
VP8BitWriterAppend(bw, &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 = VP8BitWriterAppend(bw, alpha_src, width * height);
ok = ok && !bw->error_;
} else {
ok = EncodeLossless(alpha_src, width, height, effort_level, bw, stats);
VP8BitWriterFinish(bw);
}
return ok;
}
// -----------------------------------------------------------------------------
// TODO(skal): move to dsp/ ?
static void CopyPlane(const uint8_t* src, int src_stride,
uint8_t* dst, int dst_stride, int width, int height) {
while (height-- > 0) {
memcpy(dst, src, width);
src += src_stride;
dst += dst_stride;
}
}
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;
}
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 sanity 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;
}
quant_alpha = (uint8_t*)malloc(data_size);
if (quant_alpha == NULL) {
return 0;
}
// Extract alpha data (width x height) from raw_data (stride x height).
CopyPlane(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) {
VP8BitWriter bw;
int test_filter;
uint8_t* filtered_alpha = NULL;
int try_filter_none = (effort_level > 3);
if (filter == WEBP_FILTER_FAST) { // Quick estimate of the best candidate.
const int kMinColorsForFilterNone = 16;
const int kMaxColorsForFilterNone = 192;
const int num_colors = GetNumColors(quant_alpha, width, height, width);
// For low number of colors, NONE yeilds better compression.
filter = (num_colors <= kMinColorsForFilterNone) ? WEBP_FILTER_NONE :
EstimateBestFilter(quant_alpha, width, height, width);
// For large number of colors, try FILTER_NONE in addition to the best
// filter as well.
if (num_colors > kMaxColorsForFilterNone) {
try_filter_none = 1;
}
}
// Test for WEBP_FILTER_NONE for higher effort levels.
if (try_filter_none || filter == WEBP_FILTER_NONE) {
ok = EncodeAlphaInternal(quant_alpha, width, height,
method, WEBP_FILTER_NONE, reduce_levels,
effort_level, NULL, &bw, pic->stats);
if (!ok) {
VP8BitWriterWipeOut(&bw);
goto End;
}
}
// Stop?
if (filter == WEBP_FILTER_NONE) {
goto Ok;
}
filtered_alpha = (uint8_t*)malloc(data_size);
ok = (filtered_alpha != NULL);
if (!ok) {
goto End;
}
// Try the other mode(s).
{
WebPAuxStats best_stats;
size_t best_score = try_filter_none ?
VP8BitWriterSize(&bw) : (size_t)~0U;
int wipe_tmp_bw = try_filter_none;
memset(&best_stats, 0, sizeof(best_stats)); // prevent spurious warning
if (pic->stats != NULL) best_stats = *pic->stats;
for (test_filter =
try_filter_none ? WEBP_FILTER_HORIZONTAL : WEBP_FILTER_NONE;
ok && (test_filter <= WEBP_FILTER_GRADIENT);
++test_filter) {
VP8BitWriter tmp_bw;
if (filter != WEBP_FILTER_BEST && test_filter != filter) {
continue;
}
ok = EncodeAlphaInternal(quant_alpha, width, height,
method, test_filter, reduce_levels,
effort_level, filtered_alpha, &tmp_bw,
pic->stats);
if (ok) {
const size_t score = VP8BitWriterSize(&tmp_bw);
if (score < best_score) {
// swap bitwriter objects.
VP8BitWriter tmp = tmp_bw;
tmp_bw = bw;
bw = tmp;
best_score = score;
if (pic->stats != NULL) best_stats = *pic->stats;
}
} else {
VP8BitWriterWipeOut(&bw);
}
if (wipe_tmp_bw) {
VP8BitWriterWipeOut(&tmp_bw);
}
wipe_tmp_bw = 1; // For next filter trial for WEBP_FILTER_BEST.
}
if (pic->stats != NULL) *pic->stats = best_stats;
}
Ok:
if (ok) {
*output_size = VP8BitWriterSize(&bw);
*output = VP8BitWriterBuf(&bw);
if (pic->stats != NULL) { // need stats?
pic->stats->coded_size += (int)(*output_size);
enc->sse_[3] = sse;
}
}
free(filtered_alpha);
}
End:
free(quant_alpha);
return ok;
}
//------------------------------------------------------------------------------
// Main calls
static int CompressAlphaJob(VP8Encoder* const enc, void* dummy) {
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) { // Sanity check.
free(alpha_data);
return 0;
}
enc->alpha_data_size_ = (uint32_t)alpha_size;
enc->alpha_data_ = alpha_data;
(void)dummy;
return 1;
}
void VP8EncInitAlpha(VP8Encoder* const enc) {
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_;
WebPWorkerInit(worker);
worker->data1 = enc;
worker->data2 = NULL;
worker->hook = (WebPWorkerHook)CompressAlphaJob;
}
}
int VP8EncStartAlpha(VP8Encoder* const enc) {
if (enc->has_alpha_) {
if (enc->thread_level_ > 0) {
WebPWorker* const worker = &enc->alpha_worker_;
if (!WebPWorkerReset(worker)) { // Makes sure worker is good to go.
return 0;
}
WebPWorkerLaunch(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 (!WebPWorkerSync(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_;
ok = WebPWorkerSync(worker); // finish anything left in flight
WebPWorkerEnd(worker); // still need to end the worker, even if !ok
}
free(enc->alpha_data_);
enc->alpha_data_ = NULL;
enc->alpha_data_size_ = 0;
enc->has_alpha_ = 0;
return ok;
}
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif