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remove tcoder, switch alpha-plane compression to lossless

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* Method #1 is now calling the lossless encoder on the alpha plane.
Format is not final, it's just a first draft. We need ad-hoc functions.
* removed now useless utils/alpha.*
* added utils/quant_levels.h instead
* removed the TCoder code altogether

Change-Id: I636840b6129a43171b74860e0a0fc5bb1bcffc6a
This commit is contained in:
Pascal Massimino 2012-05-21 06:22:06 -07:00
parent 831bd13168
commit 3e863dda61
13 changed files with 389 additions and 1208 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Android.mk
View File

@ -39,7 +39,6 @@ LOCAL_SRC_FILES := \
src/mux/muxedit.c \
src/mux/muxinternal.c \
src/mux/muxread.c \
src/utils/alpha.c \
src/utils/bit_reader.c \
src/utils/bit_writer.c \
src/utils/color_cache.c \
@ -47,7 +46,6 @@ LOCAL_SRC_FILES := \
src/utils/huffman.c \
src/utils/quant_levels.c \
src/utils/rescaler.c \
src/utils/tcoder.c \
src/utils/thread.c \
LOCAL_CFLAGS := -Wall -DANDROID -DHAVE_MALLOC_H -DHAVE_PTHREAD \

6
Makefile.vc
View File

@ -178,16 +178,19 @@ EX_UTIL_OBJS = \
ENC_OBJS = \
$(DIROBJ)\enc\alpha.obj \
$(DIROBJ)\enc\analysis.obj \
$(DIROBJ)\enc\backward_references.obj \
$(DIROBJ)\enc\config.obj \
$(DIROBJ)\enc\cost.obj \
$(DIROBJ)\enc\filter.obj \
$(DIROBJ)\enc\frame.obj \
$(DIROBJ)\enc\histogram.obj \
$(DIROBJ)\enc\iterator.obj \
$(DIROBJ)\enc\layer.obj \
$(DIROBJ)\enc\picture.obj \
$(DIROBJ)\enc\quant.obj \
$(DIROBJ)\enc\syntax.obj \
$(DIROBJ)\enc\tree.obj \
$(DIROBJ)\enc\vp8l.obj \
$(DIROBJ)\enc\webpenc.obj \
MUX_OBJS = \
@ -196,15 +199,14 @@ MUX_OBJS = \
$(DIROBJ)\mux\muxread.obj \
UTILS_OBJS = \
$(DIROBJ)\utils\alpha.obj \
$(DIROBJ)\utils\bit_reader.obj \
$(DIROBJ)\utils\bit_writer.obj \
$(DIROBJ)\utils\color_cache.obj \
$(DIROBJ)\utils\filters.obj \
$(DIROBJ)\utils\huffman.obj \
$(DIROBJ)\utils\huffman_encode.obj \
$(DIROBJ)\utils\quant_levels.obj \
$(DIROBJ)\utils\rescaler.obj \
$(DIROBJ)\utils\tcoder.obj \
$(DIROBJ)\utils\thread.obj \
X_OBJS = $(DEC_OBJS) $(DSP_OBJS) $(ENC_OBJS) $(MUX_OBJS) $(UTILS_OBJS) $(X_OBJS)

6
makefile.unix
View File

@ -115,7 +115,6 @@ MUX_OBJS = \
src/mux/muxread.o \
UTILS_OBJS = \
src/utils/alpha.o \
src/utils/bit_reader.o \
src/utils/bit_writer.o \
src/utils/color_cache.o \
@ -124,7 +123,6 @@ UTILS_OBJS = \
src/utils/huffman_encode.o \
src/utils/quant_levels.o \
src/utils/rescaler.o \
src/utils/tcoder.o \
src/utils/thread.o \
LIBWEBP_OBJS = $(DEC_OBJS) $(DSP_OBJS) $(ENC_OBJS) $(UTILS_OBJS)
@ -139,15 +137,13 @@ HDRS = \
src/dsp/yuv.h \
src/enc/cost.h \
src/enc/vp8enci.h \
src/utils/alpha.h \
src/utils/bit_reader.h \
src/utils/bit_writer.h \
src/utils/color_cache.h \
src/utils/filters.h \
src/utils/huffman.h \
src/utils/quant_levels.h \
src/utils/rescaler.h \
src/utils/tcoder.h \
src/utils/tcoderi.h \
src/utils/thread.h \
src/webp/decode.h \
src/webp/decode_vp8.h \

103
src/dec/alpha.c
View File

@ -11,12 +11,113 @@
#include <stdlib.h>
#include "./vp8i.h"
#include "../utils/alpha.h"
#include "../webp/decode.h"
#include "../utils/filters.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// TODO(skal): find a common place between enc/ and dec/ for these:
#define ALPHA_HEADER_LEN 2
#define ALPHA_NO_COMPRESSION 0
#define ALPHA_LOSSLESS_COMPRESSION 1
// 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;
}
}
//------------------------------------------------------------------------------
// Decodes the compressed data 'data' of size 'data_size' into the 'output'.
// The 'output' buffer should be pre-allocated and must be of the same
// dimension 'height'x'stride', as that of the image.
//
// Returns 1 on successfully decoding the compressed alpha and
// 0 if either:
// error in bit-stream header (invalid compression mode or filter), or
// error returned by appropriate compression method.
static int DecodeAlpha(const uint8_t* data, size_t data_size,
int width, int height, int stride, uint8_t* output) {
uint8_t* decoded_data = NULL;
const size_t decoded_size = height * width;
uint8_t* unfiltered_data = NULL;
WEBP_FILTER_TYPE filter;
int ok = 0;
int method;
assert(width > 0 && height > 0 && stride >= width);
assert(data != NULL && output != NULL);
if (data_size <= ALPHA_HEADER_LEN) {
return 0;
}
method = data[0] & 0x0f;
filter = data[0] >> 4;
ok = (data[1] == 0);
if (method < ALPHA_NO_COMPRESSION ||
method > ALPHA_LOSSLESS_COMPRESSION ||
filter >= WEBP_FILTER_LAST || !ok) {
return 0;
}
if (method == ALPHA_NO_COMPRESSION) {
ok = (data_size >= decoded_size);
decoded_data = (uint8_t*)data + ALPHA_HEADER_LEN;
} else {
size_t i;
int w, h;
uint32_t* const output =
(uint32_t*)WebPDecodeRGBA(data + ALPHA_HEADER_LEN,
data_size - ALPHA_HEADER_LEN,
&w, &h);
if (w != width || h != height || output == NULL) {
free(output);
return 0;
}
decoded_data = (uint8_t*)malloc(decoded_size);
if (decoded_data == NULL) {
free(output);
return 0;
}
for (i = 0; i < decoded_size; ++i) {
decoded_data[i] = (output[i] >> 8) & 0xff;
}
free(output);
}
if (ok) {
WebPFilterFunc unfilter_func = WebPUnfilters[filter];
if (unfilter_func) {
unfiltered_data = (uint8_t*)malloc(decoded_size);
if (unfiltered_data == NULL) {
if (method != ALPHA_NO_COMPRESSION) free(decoded_data);
return 0;
}
// TODO(vikas): Implement on-the-fly decoding & filter mechanism to decode
// and apply filter per image-row.
unfilter_func(decoded_data, width, height, 1, width, unfiltered_data);
// Construct raw_data (height x stride) from alpha data (height x width).
CopyPlane(unfiltered_data, width, output, stride, width, height);
free(unfiltered_data);
} else {
// Construct raw_data (height x stride) from alpha data (height x width).
CopyPlane(decoded_data, width, output, stride, width, height);
}
}
if (method != ALPHA_NO_COMPRESSION) {
free(decoded_data);
}
return ok;
}
//------------------------------------------------------------------------------
const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,

247
src/enc/alpha.c
View File

@ -13,14 +13,259 @@
#include <stdlib.h>
#include "./vp8enci.h"
#include "../utils/alpha.h"
#include "../utils/filters.h"
#include "../utils/quant_levels.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
#define ALPHA_HEADER_LEN 2
#define ALPHA_NO_COMPRESSION 0
#define ALPHA_LOSSLESS_COMPRESSION 1
// -----------------------------------------------------------------------------
// int EncodeAlpha(const uint8_t* data, int width, int height, int stride,
// int quality, int method, int filter,
// uint8_t** output, size_t* output_size)
//
// Encodes the given alpha data 'data' of size 'stride'x'height' via specified
// compression method 'method'. The pre-processing (Quantization) is
// performed if 'quality' is less than 100. For such cases, the encoding is
// lossy. Valid ranges for 'quality' is [0, 100] and 'method' is [0, 1]:
// '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 prediction mode.
// '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.
#ifdef USE_LOSSLESS_ENCODER
#include "../enc/vp8li.h"
#include "../webp/encode.h"
static int MyWriter(const uint8_t* data, size_t data_size,
const WebPPicture* const picture) {
VP8BitWriter* const bw = (VP8BitWriter*)picture->custom_ptr;
if (data_size > 0) {
VP8BitWriterAppend(bw, data, data_size);
}
return !bw->error_;
}
static int EncodeLossless(const uint8_t* data, int width, int height,
VP8BitWriter* const bw) {
int ok = 0;
WebPConfig config;
WebPPicture picture;
WebPPictureInit(&picture);
picture.width = width;
picture.height = height;
picture.use_argb_input = 1;
if (!WebPPictureAlloc(&picture)) return 0;
{
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;
}
}
picture.writer = MyWriter;
picture.custom_ptr = (void*)bw;
WebPConfigInit(&config);
config.lossless = 1;
config.method = 2;
config.quality = 100;
ok = WebPEncode(&config, &picture);
WebPPictureFree(&picture);
return ok && !bw->error_;
}
#endif
// -----------------------------------------------------------------------------
static int EncodeAlphaInternal(const uint8_t* data, int width, int height,
int method, int filter, size_t data_size,
uint8_t* tmp_alpha, VP8BitWriter* const bw) {
int ok = 0;
const uint8_t* alpha_src;
WebPFilterFunc filter_func;
uint8_t header[ALPHA_HEADER_LEN];
size_t expected_size;
#ifndef USE_LOSSLESS_ENCODER
method = ALPHA_NO_COMPRESSION;
#endif
expected_size =
(method == ALPHA_NO_COMPRESSION) ? (ALPHA_HEADER_LEN + data_size)
: (data_size >> 5);
header[0] = (filter << 4) | method;
header[1] = 0; // reserved byte for later use
VP8BitWriterInit(bw, expected_size);
VP8BitWriterAppend(bw, header, sizeof(header));
filter_func = WebPFilters[filter];
if (filter_func) {
filter_func(data, width, height, 1, 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 {
#ifdef USE_LOSSLESS_ENCODER
ok = EncodeLossless(alpha_src, width, height, bw);
VP8BitWriterFinish(bw);
#else
assert(0); // not reached.
#endif
}
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 EncodeAlpha(const uint8_t* data, int width, int height, int stride,
int quality, int method, int filter,
uint8_t** output, size_t* output_size) {
uint8_t* quant_alpha = NULL;
const size_t data_size = height * width;
int ok = 1;
// quick sanity checks
assert(data != NULL && output != NULL && output_size != NULL);
assert(width > 0 && height > 0);
assert(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(data, stride, quant_alpha, width, width, height);
if (quality < 100) { // 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, NULL);
}
if (ok) {
VP8BitWriter bw;
size_t best_score;
int test_filter;
uint8_t* filtered_alpha = NULL;
// We always test WEBP_FILTER_NONE first.
ok = EncodeAlphaInternal(quant_alpha, width, height, method,
WEBP_FILTER_NONE, data_size, NULL, &bw);
if (!ok) {
VP8BitWriterWipeOut(&bw);
goto End;
}
best_score = VP8BitWriterSize(&bw);
if (filter == WEBP_FILTER_FAST) { // Quick estimate of a second candidate?
filter = EstimateBestFilter(quant_alpha, width, height, width);
}
// 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).
for (test_filter = WEBP_FILTER_HORIZONTAL;
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,
data_size, filtered_alpha, &tmp_bw);
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;
}
} else {
VP8BitWriterWipeOut(&bw);
}
VP8BitWriterWipeOut(&tmp_bw);
}
Ok:
if (ok) {
*output_size = VP8BitWriterSize(&bw);
*output = VP8BitWriterBuf(&bw);
}
free(filtered_alpha);
}
End:
free(quant_alpha);
return ok;
}
//------------------------------------------------------------------------------
// Main calls
void VP8EncInitAlpha(VP8Encoder* enc) {
enc->has_alpha_ = (enc->pic_->a != NULL);

6
src/utils/Makefile.am
View File

@ -2,8 +2,6 @@ AM_CPPFLAGS = -I$(top_srcdir)/src
noinst_LTLIBRARIES = libwebputils.la
libwebputils_la_SOURCES =
libwebputils_la_SOURCES += alpha.c
libwebputils_la_SOURCES += alpha.h
libwebputils_la_SOURCES += bit_reader.c
libwebputils_la_SOURCES += bit_reader.h
libwebputils_la_SOURCES += bit_writer.c
@ -15,10 +13,8 @@ libwebputils_la_SOURCES += filters.h
libwebputils_la_SOURCES += huffman.c
libwebputils_la_SOURCES += huffman.h
libwebputils_la_SOURCES += quant_levels.c
libwebputils_la_SOURCES += quant_levels.h
libwebputils_la_SOURCES += rescaler.c
libwebputils_la_SOURCES += tcoder.c
libwebputils_la_SOURCES += tcoder.h
libwebputils_la_SOURCES += tcoderi.h
libwebputils_la_SOURCES += thread.c
libwebputils_la_SOURCES += thread.h

464
src/utils/alpha.c
View File

@ -1,464 +0,0 @@
// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Alpha plane encoding and decoding library.
//
// Author: vikasa@google.com (Vikas Arora)
#include <string.h> // for memcpy()
#include "./alpha.h"
#include "./bit_reader.h"
#include "./bit_writer.h"
#include "./filters.h"
#include "./tcoder.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
#define MAX_SYMBOLS 255
#define ALPHA_HEADER_LEN 2
// -----------------------------------------------------------------------------
// Zlib-like encoding using TCoder
typedef struct {
int dist; // backward distance (=0 means: literal)
int literal; // literal value (if dist = 0)
int len; // length of matched string for non-literal
} Token;
#define MIN_LEN 2
#define DEFER_SKIP 1 // for deferred evaluation (0 = off)
#define CACHED_COST(coder, c) ((cost_cache[(c)] == 0.) ? \
(cost_cache[(c)] = lit_mode_cost + TCoderSymbolCost((coder), (c))) \
: cost_cache[(c)])
// Record symbol
#define RECORD(TOKEN) { \
TCoderEncode(coderd, (TOKEN)->dist, NULL); \
if ((TOKEN)->dist == 0) { \
TCoderEncode(coder, (TOKEN)->literal, NULL); \
} else { \
TCoderEncode(coderl, (TOKEN)->len - MIN_LEN, NULL); \
} \
}
static int GetLongestMatch(const uint8_t* const data,
const uint8_t* const ref, int max_len) {
int n;
for (n = 0; (n < max_len) && (data[n] == ref[n]); ++n) { /* do nothing */ }
return n;
}
static int EncodeZlibTCoder(const uint8_t* data, int width, int height,
VP8BitWriter* const bw) {
int ok = 0;
const int data_len = width * height;
const int MAX_DIST = 3 * width;
const int MAX_LEN = 2 * width;
Token* const msg = (Token*)malloc(data_len * sizeof(*msg));
int num_tokens;
TCoder* const coder = TCoderNew(MAX_SYMBOLS);
TCoder* const coderd = TCoderNew(MAX_DIST);
TCoder* const coderl = TCoderNew(MAX_LEN - MIN_LEN);
if (coder == NULL || coderd == NULL || coderl == NULL) {
goto End;
}
if (msg == NULL) {
goto End;
}
{
int deferred_eval = 0;
int n = 0;
num_tokens = 0;
while (n < data_len) {
const double lit_mode_cost = TCoderSymbolCost(coderd, 0);
double cost_cache[MAX_SYMBOLS + 1] = { 0. };
Token best;
int dist = 0;
double best_cost = CACHED_COST(coder, data[n]);
const int max_len = (MAX_LEN > data_len - n) ? data_len - n : MAX_LEN;
best.dist = 0;
best.literal = data[n];
best.len = 1;
for (dist = 1; dist <= MAX_DIST && dist <= n; ++dist) {
const int pos = n - dist;
const int min_len = best.len - 1;
int len;
// Early out: we probe at two locations for a quick match check
if (data[pos] != data[n] ||
data[pos + min_len] != data[n + min_len]) {
continue;
}
len = GetLongestMatch(data + pos, data + n, max_len);
if (len >= MIN_LEN && len >= best.len) {
// This is the cost of the coding proposal
const double cost = TCoderSymbolCost(coderl, len - MIN_LEN)
+ TCoderSymbolCost(coderd, dist);
// We're gaining an extra len-best.len coded message over the last
// known best. Compute how this would have cost if coded all literal.
// (TODO: we should fully re-evaluate at position best.len and not
// assume all is going be coded as literals. But it's at least an
// upper-bound (worst-case coding). Deferred evaluation used below
// partially addresses this.
double lit_cost = 0;
int i;
for (i = best.len; i < len; ++i) {
lit_cost += CACHED_COST(coder, data[n + i]);
}
// So, is it worth ?
if (best_cost + lit_cost >= cost) {
best_cost = cost;
best.len = len;
best.dist = dist;
}
}
if (len >= max_len) {
break; // No need to search further. We already got a max-long match
}
}
// Deferred evaluation: before finalizing a choice we try to find
// best cost at position n + 1 and see if we get a longer
// match then current best. If so, we transform the current match
// into a literal, go to position n + 1, and try again.
{
Token* cur = &msg[num_tokens];
int forget = 0;
if (deferred_eval) {
--cur;
// If the next match isn't longer, keep previous match
if (best.len <= cur->len) {
deferred_eval = 0;
n += cur->len - DEFER_SKIP;
forget = 1; // forget the new match
RECORD(cur)
} else { // else transform previous match into a shorter one
cur->len = DEFER_SKIP;
if (DEFER_SKIP == 1) {
cur->dist = 0; // literal
}
// TODO(later): RECORD() macro should be changed to take an extra
// "is_final" param, so that we could write the bitstream at once.
RECORD(cur)
++cur;
}
}
if (!forget) {
*cur = best;
++num_tokens;
if (DEFER_SKIP > 0) {
deferred_eval = (cur->len > 2) && (cur->len < MAX_LEN / 2);
}
if (deferred_eval) {
// will probe at a later position before finalizing.
n += DEFER_SKIP;
} else {
// Keep the current choice.
n += cur->len;
RECORD(cur)
}
}
}
}
}
// Final bitstream assembly.
{
int n;
TCoderInit(coder);
TCoderInit(coderd);
TCoderInit(coderl);
for (n = 0; n < num_tokens; ++n) {
const Token* const t = &msg[n];
const int is_literal = (t->dist == 0);
TCoderEncode(coderd, t->dist, bw);
if (is_literal) { // literal
TCoderEncode(coder, t->literal, bw);
} else {
TCoderEncode(coderl, t->len - MIN_LEN, bw);
}
}
ok = 1;
}
End:
if (coder) TCoderDelete(coder);
if (coderl) TCoderDelete(coderl);
if (coderd) TCoderDelete(coderd);
free(msg);
return ok && !bw->error_;
}
// -----------------------------------------------------------------------------
static int EncodeAlphaInternal(const uint8_t* data, int width, int height,
int method, int filter, size_t data_size,
uint8_t* tmp_alpha, VP8BitWriter* const bw) {
int ok = 0;
const uint8_t* alpha_src;
WebPFilterFunc filter_func;
uint8_t header[ALPHA_HEADER_LEN];
const size_t expected_size = (method == 0) ?
(ALPHA_HEADER_LEN + data_size) : (data_size >> 5);
header[0] = (filter << 4) | method;
header[1] = 0; // reserved byte for later use
VP8BitWriterInit(bw, expected_size);
VP8BitWriterAppend(bw, header, sizeof(header));
filter_func = WebPFilters[filter];
if (filter_func) {
filter_func(data, width, height, 1, width, tmp_alpha);
alpha_src = tmp_alpha;
} else {
alpha_src = data;
}
if (method == 0) {
ok = VP8BitWriterAppend(bw, alpha_src, width * height);
ok = ok && !bw->error_;
} else {
ok = EncodeZlibTCoder(alpha_src, width, height, bw);
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;
}
}
int EncodeAlpha(const uint8_t* data, int width, int height, int stride,
int quality, int method, int filter,
uint8_t** output, size_t* output_size) {
uint8_t* quant_alpha = NULL;
const size_t data_size = height * width;
int ok = 1;
// quick sanity checks
assert(data != NULL && output != NULL && output_size != NULL);
assert(width > 0 && height > 0);
assert(stride >= width);
assert(filter >= WEBP_FILTER_NONE && filter <= WEBP_FILTER_FAST);
if (quality < 0 || quality > 100) {
return 0;
}
if (method < 0 || method > 1) {
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(data, stride, quant_alpha, width, width, height);
if (quality < 100) { // 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, NULL);
}
if (ok) {
VP8BitWriter bw;
size_t best_score;
int test_filter;
uint8_t* filtered_alpha = NULL;
// We always test WEBP_FILTER_NONE first.
ok = EncodeAlphaInternal(quant_alpha, width, height, method,
WEBP_FILTER_NONE, data_size, NULL, &bw);
if (!ok) {
VP8BitWriterWipeOut(&bw);
goto End;
}
best_score = VP8BitWriterSize(&bw);
if (filter == WEBP_FILTER_FAST) { // Quick estimate of a second candidate?
filter = EstimateBestFilter(quant_alpha, width, height, width);
}
// 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).
for (test_filter = WEBP_FILTER_HORIZONTAL;
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,
data_size, filtered_alpha, &tmp_bw);
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;
}
} else {
VP8BitWriterWipeOut(&bw);
}
VP8BitWriterWipeOut(&tmp_bw);
}
Ok:
if (ok) {
*output_size = VP8BitWriterSize(&bw);
*output = VP8BitWriterBuf(&bw);
}
free(filtered_alpha);
}
End:
free(quant_alpha);
return ok;
}
// -----------------------------------------------------------------------------
// Alpha Decode.
static int DecompressZlibTCoder(VP8BitReader* const br, int width,
uint8_t* output, size_t output_size) {
int ok = 0;
const int MAX_DIST = 3 * width;
const int MAX_LEN = 2 * width;
TCoder* const coder = TCoderNew(MAX_SYMBOLS);
TCoder* const coderd = TCoderNew(MAX_DIST);
TCoder* const coderl = TCoderNew(MAX_LEN - MIN_LEN);
if (coder == NULL || coderd == NULL || coderl == NULL) {
goto End;
}
{
size_t pos = 0;
assert(br != NULL);
while (pos < output_size && !br->eof_) {
const size_t dist = TCoderDecode(coderd, br);
if (dist == 0) {
output[pos] = TCoderDecode(coder, br);
++pos;
} else {
const size_t len = MIN_LEN + TCoderDecode(coderl, br);
size_t k;
if (pos + len > output_size || pos < dist) goto End;
for (k = 0; k < len; ++k) {
output[pos + k] = output[pos + k - dist];
}
pos += len;
}
}
ok = !br->eof_;
}
End:
if (coder) TCoderDelete(coder);
if (coderl) TCoderDelete(coderl);
if (coderd) TCoderDelete(coderd);
return ok;
}
// -----------------------------------------------------------------------------
int DecodeAlpha(const uint8_t* data, size_t data_size,
int width, int height, int stride,
uint8_t* output) {
uint8_t* decoded_data = NULL;
const size_t decoded_size = height * width;
uint8_t* unfiltered_data = NULL;
WEBP_FILTER_TYPE filter;
int ok = 0;
int method;
assert(width > 0 && height > 0 && stride >= width);
assert(data != NULL && output != NULL);
if (data_size <= ALPHA_HEADER_LEN) {
return 0;
}
method = data[0] & 0x0f;
filter = data[0] >> 4;
ok = (data[1] == 0);
if (method < 0 || method > 1 ||
filter > WEBP_FILTER_GRADIENT || !ok) {
return 0;
}
if (method == 0) {
ok = (data_size >= decoded_size);
decoded_data = (uint8_t*)data + ALPHA_HEADER_LEN;
} else if (method == 1) {
VP8BitReader br;
decoded_data = (uint8_t*)malloc(decoded_size);
if (decoded_data == NULL) {
return 0;
}
VP8InitBitReader(&br, data + ALPHA_HEADER_LEN, data + data_size);
ok = DecompressZlibTCoder(&br, width, decoded_data, decoded_size);
}
if (ok) {
WebPFilterFunc unfilter_func = WebPUnfilters[filter];
if (unfilter_func) {
unfiltered_data = (uint8_t*)malloc(decoded_size);
if (unfiltered_data == NULL) {
if (method == 1) free(decoded_data);
return 0;
}
// TODO(vikas): Implement on-the-fly decoding & filter mechanism to decode
// and apply filter per image-row.
unfilter_func(decoded_data, width, height, 1, width, unfiltered_data);
// Construct raw_data (height x stride) from alpha data (height x width).
CopyPlane(unfiltered_data, width, output, stride, width, height);
free(unfiltered_data);
} else {
// Construct raw_data (height x stride) from alpha data (height x width).
CopyPlane(decoded_data, width, output, stride, width, height);
}
}
if (method == 1) {
free(decoded_data);
}
return ok;
}
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif

69
src/utils/alpha.h
View File

@ -1,69 +0,0 @@
// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Alpha plane encoding and decoding library.
//
// Author: vikasa@google.com (Vikas Arora)
#ifndef WEBP_UTILS_ALPHA_H_
#define WEBP_UTILS_ALPHA_H_
#include <stdlib.h>
#include "../webp/types.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// Encodes the given alpha data 'data' of size 'stride'x'height' via specified
// compression method 'method'. The pre-processing (Quantization) is
// performed if 'quality' is less than 100. For such cases, the encoding is
// lossy. Valid ranges for 'quality' is [0, 100] and 'method' is [0, 1]:
// 'method = 0' - No compression;
// 'method = 1' - Backward reference counts encoded with arithmetic encoder;
// '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 prediction mode.
// '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.
int EncodeAlpha(const uint8_t* data, int width, int height, int stride,
int quality, int method, int filter,
uint8_t** output, size_t* output_size);
// Decodes the compressed data 'data' of size 'data_size' into the 'output'.
// The 'output' buffer should be pre-allocated and must be of the same
// dimension 'height'x'stride', as that of the image.
//
// Returns 1 on successfully decoding the compressed alpha and
// 0 if either:
// error in bit-stream header (invalid compression mode or filter), or
// error returned by appropriate compression method.
int DecodeAlpha(const uint8_t* data, size_t data_size,
int width, int height, int stride, uint8_t* output);
// Replace the input 'data' of size 'width'x'height' with 'num-levels'
// quantized values. If not NULL, 'mse' will contain the mean-squared error.
// Valid range for 'num_levels' is [2, 256].
// Returns false in case of error (data is NULL, or parameters are invalid).
int QuantizeLevels(uint8_t* data, int width, int height, int num_levels,
float* mse);
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
#endif /* WEBP_UTILS_ALPHA_H_ */

2
src/utils/quant_levels.c
View File

@ -13,7 +13,7 @@
#include <assert.h>
#include <math.h> // for sqrt()
#include "./alpha.h"
#include "./quant_levels.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {

34
src/utils/quant_levels.h Normal file
View File

@ -0,0 +1,34 @@
// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Alpha plane quantization utility
//
// Author: vikasa@google.com (Vikas Arora)
#ifndef WEBP_UTILS_QUANT_LEVELS_H_
#define WEBP_UTILS_QUANT_LEVELS_H_
#include <stdlib.h>
#include "../webp/types.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// Replace the input 'data' of size 'width'x'height' with 'num-levels'
// quantized values. If not NULL, 'mse' will contain the mean-squared error.
// Valid range for 'num_levels' is [2, 256].
// Returns false in case of error (data is NULL, or parameters are invalid).
int QuantizeLevels(uint8_t* data, int width, int height, int num_levels,
float* mse);
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
#endif /* WEBP_UTILS_QUANT_LEVELS_H_ */

497
src/utils/tcoder.c
View File

@ -1,497 +0,0 @@
// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Tree-coder using VP8's boolean coder
//
// Author: Skal (pascal.massimino@gmail.com)
//
// Rationale:
// We extend the boolean (binary) coder to handle arbitrary-sized alphabets,
// and not just binary ones.
// We dynamically maintain the population count and use the locally-optimal
// probability distribution for coding every symbol. Every symbol can be
// coded using _any_ binary tree. The boolean coder would traverse it and
// branch each nodes left and right with the accumulated probability.
//
// E.g. with 3 symbols A, B, C already coded 30, 50 and 120 times respectively:
//
/* Root Node #0 (count=30+50+120=200)
| \
| A (count=30)
Inner-Node #1 (count=50+120=170)
| \
| C (count=120)
B (count=50)
*/
// If the next symbol to code is "C", we'll first code '0' with probability
// p0 = 170/200 (which is the probability of taking the left branch at the
// Root Node #0) and then code '1' with a probability p1 = 120/170 (which
// is the probability of taking the right branch at the Inner-Node #1). The
// total probability p0 * p1 = 120 / 200 is the correct one for symbol 'C'
// (up to small rounding differences in the boolean coder).
// The alphabet could be coded with _any_ tree, provided the count at the
// inner nodes are updated appropriately. Put otherwise, the binary tree
// is only used to efficiently update the frequency counts in O(ln(N)) time
// instead of O(N).
// For instance, we could use the equivalent tree:
/* Root (count=200)
| \
| C (count=120)
Inner (count=50+30=80)
| \
| B (count=50)
A (count=30)
*/
// The frequency distribution would still be respected when coding the symbols.
// But! There's a noticeable difference: it only takes _one_ call to VP8PutBit()
// when coding the letter 'C' (with probability 120/200), which is the most
// frequent symbol. This has an impact on speed, considering that each call
// to VP8PutBit/VP8GetBit is costly. Hence, in order to minimize the number
// of binary coding, the frequent symbol should be up in the tree.
// Using Huffman tree is a solution, but the management and updating can be
// quite complicated. Here we opt for a simpler option: we use _ternary_
// tree instead, where each inner node can be associated with a symbol, in
// addition to the regular left/right branches. When we traverse down
// the tree, a stop bit is used to signal whether the traversal is finished
// or not. Its probability is proportional to the frequency with which the
// node's symbol has been seen (see probaS_). If the traversal is not
// finished, we keep branching right or left according with a probability
// proportional to each branch's use count (see probaL_).
// When a symbol is seen more frequently than its parent, we simply
// exchange the two symbols without changing the tree structure or the
// left/right branches.
// Hence, both tree examples above can be coded using this ternary tree:
/* Root #0 (count=200)
/ | \
/ C \
Node #1 Node #2
/ | \ / | \
x A x x B x <- where 'x' means un-assigned branches.
*/
// Here, if the symbol 'A' becomes more frequent afterward, we'll just swap it
// with 'C' (cf ExchangeSymbol()) without reorganizing the tree.
//
// Using this simple maintenance, we observed a typical 10-20% reduction
// in the number of calls to VP8PutBit(), leading to 3-5% speed gain.
//
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "./tcoderi.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
#if defined(_MSC_VER) && !defined(NOT_HAVE_LOG2)
# define NOT_HAVE_LOG2 1
#endif
#ifdef NOT_HAVE_LOG2
static double log2(double d) {
const double kLog2Reciprocal = 1.442695040888963;
return log(d) * kLog2Reciprocal;
}
#endif
// For code=00001xxx..., returns the position of the leftmost leading '1' bit.
static WEBP_INLINE int CodeLength(int code) {
int length = 0;
if (code > 0) {
while ((code >> length) != 1) ++length;
}
return length;
}
// -----------------------------------------------------------------------------
TCoder* TCoderNew(int max_symbol) {
const int num_nodes = max_symbol + 1;
TCoder* c;
uint8_t* memory;
int size;
if (max_symbol < 0 || max_symbol >= TCODER_MAX_SYMBOL) {
return NULL;
}
size = sizeof(*c) + num_nodes * sizeof(*c->nodes_)
+ num_nodes * sizeof(*c->symbols_);
memory = (uint8_t*)malloc(size);
if (memory == NULL) return NULL;
c = (TCoder*)memory;
memory += sizeof(*c);
c->nodes_ = (Node*)memory - 1;
memory += num_nodes * sizeof(*c->nodes_);
c->symbols_ = (int*)memory;
c->num_nodes_ = num_nodes;
c->frozen_ = 0;
TCoderInit(c);
return c;
}
static WEBP_INLINE void ResetNode(Node* const node, Symbol_t symbol) {
assert(node);
node->countS_ = (Count_t)0;
node->count_ = (Count_t)0;
node->probaS_ = HALF_PROBA;
node->probaL_ = HALF_PROBA;
node->symbol_ = symbol;
}
// Wipe the tree clean.
static void ResetTree(TCoder* const c) {
int pos;
assert(c);
c->num_symbols_ = 0;
c->total_coded_ = 0;
for (pos = 1; pos <= c->num_nodes_; ++pos) {
ResetNode(&c->nodes_[pos], INVALID_SYMBOL);
}
c->fixed_symbols_ = 0;
c->symbol_bit_cost_ = 5 + CodeLength(c->num_nodes_);
}
static void ResetSymbolMap(TCoder* const c) {
Symbol_t s;
assert(c);
c->num_symbols_ = 0;
for (s = 0; s < c->num_nodes_; ++s) {
c->symbols_[s] = INVALID_POS;
}
}
void TCoderInit(TCoder* const c) {
assert(c);
if (!c->frozen_) { // Reset counters
ResetTree(c);
ResetSymbolMap(c);
}
}
void TCoderDelete(TCoder* const c) {
free(c);
}
// -----------------------------------------------------------------------------
// Tree utils around nodes
// Total number of visits on this nodes
static WEBP_INLINE Count_t TotalCount(const Node* const n) {
return n->countS_ + n->count_;
}
// Returns true if node has no child.
static WEBP_INLINE int IsLeaf(const TCoder* const c, int pos) {
return (2 * pos > c->num_symbols_);
}
// Returns true if node has no right child.
static WEBP_INLINE int HasOnlyLeftChild(const TCoder* const c, int pos) {
return (2 * pos == c->num_symbols_);
}
// -----------------------------------------------------------------------------
// Node management
static int NewNode(TCoder* const c, int s) {
// For an initial new symbol position, we pick the slot that is the
// closest to the top of the tree. It shortens the paths' length.
const int pos = 1 + c->num_symbols_;
assert(c);
assert(c->num_symbols_ < c->num_nodes_);
assert(c->symbols_[s] == INVALID_POS);
assert(c->nodes_[pos].symbol_ == INVALID_SYMBOL);
c->symbols_[s] = pos;
ResetNode(&c->nodes_[pos], s);
++c->num_symbols_;
return pos;
}
// trivial method, mainly for debug
static WEBP_INLINE int SymbolToNode(const TCoder* const c, int s) {
const int pos = c->symbols_[s];
assert(s >= 0 && s < c->num_nodes_ && s != INVALID_SYMBOL);
assert(pos != INVALID_POS);
assert(c->nodes_[pos].symbol_ == s);
return pos;
}
#define SWAP(T, a, b) do { \
const T tmp = (a); \
(a) = (b); \
(b) = tmp; \
} while (0)
// Make child symbol bubble up one level
static void ExchangeSymbol(const TCoder* const c, const int pos) {
const int parent = pos >> 1;
Node* const node0 = &c->nodes_[parent]; // parent node
Node* const node1 = &c->nodes_[pos]; // child node
const Symbol_t S0 = node0->symbol_;
const Symbol_t S1 = node1->symbol_;
c->symbols_[S1] = parent;
c->symbols_[S0] = pos;
assert(node1->countS_ >= node0->countS_);
node0->count_ -= (node1->countS_ - node0->countS_);
assert(node0->count_ > 0);
SWAP(Count_t, node0->countS_, node1->countS_);
SWAP(Symbol_t, node0->symbol_, node1->symbol_);
// Note: probaL_ and probaS_ are recomputed. No need to SWAP them.
}
#undef SWAP
// -----------------------------------------------------------------------------
// probability computation
static WEBP_INLINE int CalcProba(Count_t num, Count_t total, int max_proba) {
int p;
assert(total > 0);
p = num * max_proba / total;
assert(p >= 0 && p <= MAX_PROBA);
return MAX_PROBA - p;
}
static WEBP_INLINE void UpdateNodeProbas(TCoder* const c, int pos) {
Node* const node = &c->nodes_[pos];
const Count_t total = TotalCount(node);
if (total < COUNTER_CUT_OFF)
node->probaS_ = CalcProba(node->countS_, total, MAX_PROBA);
if (!IsLeaf(c, pos)) {
const Count_t total_count = node->count_;
if (total_count < COUNTER_CUT_OFF) {
const Count_t left_count = TotalCount(&c->nodes_[2 * pos]);
node->probaL_ =
MAX_PROBA - CalcProba(left_count, total_count, MAX_PROBA);
}
}
}
static void UpdateProbas(TCoder* const c, int pos) {
for ( ; pos >= 1; pos >>= 1) {
UpdateNodeProbas(c, pos);
}
}
// -----------------------------------------------------------------------------
static void UpdateTree(TCoder* const c, int pos) {
Node* node = &c->nodes_[pos];
const int is_fresh_new_symbol = (node->countS_ == 0);
assert(c);
assert(pos >= 1 && pos <= c->num_nodes_);
assert(node->symbol_ != INVALID_SYMBOL);
if (!(c->frozen_ || node->countS_ >= COUNTER_CUT_OFF) ||
is_fresh_new_symbol) {
const int starting_pos = pos; // save for later
// Update the counters up the tree, possibly exchanging some nodes
++node->countS_;
while (pos > 1) {
Node* const parent = &c->nodes_[pos >> 1];
++parent->count_;
if (parent->countS_ < node->countS_) {
ExchangeSymbol(c, pos);
}
pos >>= 1;
node = parent;
}
++c->total_coded_;
UpdateProbas(c, starting_pos); // Update the probas along the modified path
}
}
// -----------------------------------------------------------------------------
// Fixed-length symbol coding
// Note: the symbol will be coded exactly once at most, so using a fixed length
// code is better than Golomb-code (e.g.) on average.
// We use the exact bit-distribution probability considering the upper-bound
// supplied:
// Written in binary, a symbol 's' has a probability of having its k-th bit
// set to 1 which is given by:
// If the k-th bit of max_value is 0:
// P0(k) = [(max_value >> (k + 1)) << k] / max_value
// If the k-th bit of max_value is 1:
// P1(k) = P0(k) + [max_value & ((1 << k) - 1)] / max_value
static WEBP_INLINE void CodeSymbol(VP8BitWriter* const bw, int s,
int max_value) {
int i, up = 1;
assert(bw);
assert(s < max_value);
for (i = 0; up < max_value; up <<= 1, ++i) {
int den = (max_value >> 1) & ~(up - 1);
if (max_value & up) den |= max_value & (up - 1);
VP8PutBit(bw, (s >> i) & 1, MAX_PROBA - MAX_PROBA * den / max_value);
}
}
static WEBP_INLINE int DecodeSymbol(VP8BitReader* const br, int max_value) {
int i, up = 1, v = 0;
assert(br);
for (i = 0; up < max_value; ++i) {
int den = (max_value >> 1) & ~(up - 1);
if (max_value & up) den |= max_value & (up - 1);
v |= VP8GetBit(br, MAX_PROBA - MAX_PROBA * den / max_value) << i;
up <<= 1;
}
return v;
}
// -----------------------------------------------------------------------------
// Encoding
void TCoderEncode(TCoder* const c, int s, VP8BitWriter* const bw) {
int pos;
const int is_new_symbol = (c->symbols_[s] == INVALID_POS);
assert(c);
assert(s >= 0 && s < c->num_nodes_);
if (!c->fixed_symbols_ && c->num_symbols_ < c->num_nodes_) {
if (c->num_symbols_ > 0) {
if (bw != NULL) {
const int new_symbol_proba =
CalcProba(c->num_symbols_, c->total_coded_, HALF_PROBA - 1);
VP8PutBit(bw, is_new_symbol, new_symbol_proba);
}
} else {
assert(is_new_symbol);
}
} else {
assert(!is_new_symbol);
}
if (is_new_symbol) {
if (bw != NULL) {
int k, count = 0;
for (k = 0; k < s; ++k) {
count += (c->symbols_[k] == INVALID_POS);
}
CodeSymbol(bw, count, c->num_nodes_ - c->num_symbols_);
}
pos = NewNode(c, s);
} else {
pos = SymbolToNode(c, s);
if (bw != NULL) {
const int length = CodeLength(pos);
int parent = 1;
int i;
for (i = 0; !IsLeaf(c, parent); ++i) {
const Node* const node = &c->nodes_[parent];
const int symbol_proba = node->probaS_;
const int is_stop = (i == length);
if (VP8PutBit(bw, is_stop, symbol_proba)) {
break;
} else if (!HasOnlyLeftChild(c, parent)) {
const int left_proba = node->probaL_;
const int is_right =
(pos >> (length - 1 - i)) & 1; // extract bits #i
VP8PutBit(bw, is_right, left_proba);
parent = (parent << 1) | is_right;
} else {
parent <<= 1;
break;
}
}
assert(parent == pos);
}
}
UpdateTree(c, pos);
}
// -----------------------------------------------------------------------------
// Decoding
int TCoderDecode(TCoder* const c, VP8BitReader* const br) {
int s;
int pos;
int is_new_symbol = 0;
assert(c);
assert(br);
// Check if we need to transmit the new symbol's value
if (!c->fixed_symbols_ && c->num_symbols_ < c->num_nodes_) {
if (c->num_symbols_ > 0) {
const int new_symbol_proba =
CalcProba(c->num_symbols_, c->total_coded_, HALF_PROBA - 1);
is_new_symbol = VP8GetBit(br, new_symbol_proba);
} else {
is_new_symbol = 1;
}
}
// Code either the raw value, or the path downward to its node.
if (is_new_symbol) {
int count = DecodeSymbol(br, c->num_nodes_ - c->num_symbols_);
// The 'count' value specifies the number of empty slots to jump
// over. We skip the already-used ones.
for (s = 0; s < c->num_nodes_; ++s) {
if (c->symbols_[s] == INVALID_POS) {
if (count-- == 0) break;
}
}
if (s == c->num_nodes_) {
goto Error;
}
pos = NewNode(c, s);
} else {
pos = 1;
while (!IsLeaf(c, pos)) {
const Node* const node = &c->nodes_[pos];
// Did we reach the stopping node?
const int symbol_proba = node->probaS_;
const int is_stop = VP8GetBit(br, symbol_proba);
if (is_stop) {
break; // reached the stopping node for the coded symbol.
} else {
// Not yet done, keep traversing and branching.
if (!HasOnlyLeftChild(c, pos)) {
const int left_proba = node->probaL_;
const int is_right = VP8GetBit(br, left_proba);
pos = (pos << 1) | is_right;
} else {
pos <<= 1;
break;
}
assert(pos <= c->num_nodes_);
}
}
assert(pos <= c->num_symbols_);
s = c->nodes_[pos].symbol_;
assert(pos == SymbolToNode(c, s));
}
assert(pos <= c->num_symbols_);
UpdateTree(c, pos);
return s;
Error:
br->eof_ = 1; // will make decoding abort.
return 0;
}
// -----------------------------------------------------------------------------
double TCoderSymbolCost(const TCoder* const c, int symbol) {
const int pos = c->symbols_[symbol];
assert(c);
assert(symbol >= 0 && symbol < c->num_nodes_);
if (pos != INVALID_POS) {
const Node* const node = &c->nodes_[pos];
const Count_t count = node->countS_;
assert(count > 0);
assert(c->total_coded_ > 0);
// Note: we use 1 + total_coded_ as denominator because we most probably
// intend to code an extra symbol afterward.
// TODO(skal): is log2() too slow ?
return -log2(count / (1. + c->total_coded_));
}
return c->symbol_bit_cost_;
}
// -----------------------------------------------------------------------------
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif

86
src/utils/tcoder.h
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@ -1,86 +0,0 @@
// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Tree-coder using VP8's boolean coder
//
// Symbols are stored as nodes of a tree that records their frequencies and
// is dynamically updated.
//
// Author: Skal (pascal.massimino@gmail.com)
//
// Encoding example:
/*
static int Compress(const uint8_t* src, int src_length,
uint8_t** output, size_t* output_size) {
int i;
TCoder* coder = TCoderNew(255);
VP8BitWriter bw;
VP8BitWriterInit(&bw, 0);
for (i = 0; i < src_length; ++i)
TCoderEncode(coder, src[i], &bw);
TCoderDelete(coder);
VP8BitWriterFinish(&bw);
*output = VP8BitWriterBuf(&bw);
*output_size = VP8BitWriterSize(&bw);
return !bw.error_;
}
*/
//
// Decoding example:
/*
static int Decompress(const uint8_t* src, size_t src_size,
uint8_t* dst, int dst_length) {
int i;
TCoder* coder = TCoderNew(255);
VP8BitReader br;
VP8InitBitReader(&br, src, src + src_size);
for (i = 0; i < dst_length; ++i)
dst[i] = TCoderDecode(coder, &br);
TCoderDelete(coder);
return !br.eof_;
}
*/
#ifndef WEBP_UTILS_TCODER_H_
#define WEBP_UTILS_TCODER_H_
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
struct VP8BitReader;
struct VP8BitWriter;
typedef struct TCoder TCoder;
// Creates a tree-coder capable of coding symbols in
// the [0, max_symbol] range. Returns NULL in case of memory error.
// 'max_symbol' must be in the range [0, TCODER_MAX_SYMBOL)
#define TCODER_MAX_SYMBOL (1 << 24)
TCoder* TCoderNew(int max_symbol);
// Re-initialize an existing object, make it ready for a new encoding or
// decoding cycle.
void TCoderInit(TCoder* const c);
// destroys the tree-coder object and frees memory.
void TCoderDelete(TCoder* const c);
// Code next symbol 's'. If the bit-writer 'bw' is NULL, the function will
// just record the symbol, and update the internal frequency counters.
void TCoderEncode(TCoder* const c, int s, struct VP8BitWriter* const bw);
// Decode and return next symbol.
int TCoderDecode(TCoder* const c, struct VP8BitReader* const br);
// Theoretical number of bits needed to code 'symbol' in the current state.
double TCoderSymbolCost(const TCoder* const c, int symbol);
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
#endif // WEBP_UTILS_TCODER_H_

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src/utils/tcoderi.h
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// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Internal header for tree-coder
//
// Author: Skal (pascal.massimino@gmail.com)
//
#ifndef WEBP_UTILS_TCODERI_H_
#define WEBP_UTILS_TCODERI_H_
#include "./tcoder.h"
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "../utils/bit_reader.h"
#include "../utils/bit_writer.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
typedef int Symbol_t;
typedef uint32_t Count_t; // TODO(skal): check overflow during coding.
#define INVALID_SYMBOL ((Symbol_t)(-1))
#define INVALID_POS 0
#define MAX_PROBA 255
#define HALF_PROBA 128
// Limit the number of tree updates above which we freeze the probabilities.
// Mainly for speed reason.
// TODO(skal): could be a bitstream parameter?
#define COUNTER_CUT_OFF 16383
typedef struct { // ternary node.
Symbol_t symbol_;
// Note: theoretically, one of this three field is redundant and could be
// omitted, but it'd make the code quite complicated (having to look-up the
// parent's total count in order to deduce the missing field). Better not.
Count_t countS_; // count for symbol
Count_t count_; // count for non-symbol (derived from sub-tree)
int probaL_; // cached left proba = TotalCount(left) / count_
int probaS_; // cached approximate proba = countS_ / TotalCount
} Node;
struct TCoder {
// dynamic fields:
int num_symbols_; // number of symbols actually used
Count_t total_coded_; // total number of coded symbols
int frozen_; // if true, frequencies are not updated
int fixed_symbols_; // if true, symbols are not updated
// constants:
int num_nodes_; // max number of symbols or nodes. Constant, > 0.
double symbol_bit_cost_; // latest evaluation of the bit-cost per new symbol
Node* nodes_; // nodes (1-based indexed)
int* symbols_; // for each symbol, location of its node
};
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
#endif // WEBP_UTILS_TCODERI_H_