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Increase the transform bits if possible.
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This brings minor size improvements because repetitive values in
the transform images are easily explainable through LZ77. Still,
it makes an upcoming pull request a bit more stable.

Change-Id: I1c7135675cb59b5e27ca960738d74465f10d0deb
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@vrabaud
vrabaud committed May 17, 2024
1 parent 1bf198a commit 971a03d
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Showing 3 changed files with 98 additions and 28 deletions.
77 changes: 74 additions & 3 deletions src/enc/predictor_enc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,8 @@
// Urvang Joshi (urvang@google.com)
// Vincent Rabaud (vrabaud@google.com)

#include <string.h>

#include "src/dsp/lossless.h"
#include "src/dsp/lossless_common.h"
#include "src/enc/vp8i_enc.h"
Expand Down Expand Up @@ -467,6 +469,72 @@ static void CopyImageWithPrediction(int width, int height, int bits,
}
}

// Checks whether 'image' is sub-samplable by finding the biggest power of 2
// squares (defined by 'best_bits') of uniform value it is made out of.
static void OptimizeSampling(uint32_t* const image, int full_width,
int full_height, int bits, int* best_bits_out) {
int width = VP8LSubSampleSize(full_width, bits);
int height = VP8LSubSampleSize(full_height, bits);
int old_width, x, y, square_size;
int best_bits = bits;
*best_bits_out = bits;
// Check rows first.
while (best_bits < MAX_TRANSFORM_BITS) {
const int new_square_size = 1 << (best_bits + 1 - bits);
int is_good = 1;
square_size = 1 << (best_bits - bits);
for (y = 0; y + new_square_size <= height; y += new_square_size) {
// Check the first lines of consecutive line groups.
if (memcmp(&image[y * width], &image[(y + square_size) * width],
width * sizeof(*image)) != 0) {
is_good = 0;
break;
}
}
if (is_good) {
++best_bits;
} else {
break;
}
}
if (best_bits == bits) return;

// Check columns.
while (best_bits > bits) {
int is_good = 1;
square_size = 1 << (best_bits - bits);
for (y = 0; is_good && y < height; ++y) {
for (x = 0; is_good && x + square_size <= width; x += square_size) {
int i;
for (i = 1; i < square_size; ++i) {
if (image[y * width + x + i] != image[y * width + x]) {
is_good = 0;
break;
}
}
}
}
if (is_good) {
break;
} else {
--best_bits;
}
}
if (best_bits == bits) return;

// Subsample the image.
old_width = width;
square_size = 1 << (best_bits - bits);
width = VP8LSubSampleSize(full_width, best_bits);
height = VP8LSubSampleSize(full_height, best_bits);
for (y = 0; y < height; ++y) {
for (x = 0; x < width; ++x) {
image[y * width + x] = image[square_size * (y * old_width + x)];
}
}
*best_bits_out = best_bits;
}

// Finds the best predictor for each tile, and converts the image to residuals
// with respect to predictions. If near_lossless_quality < 100, applies
// near lossless processing, shaving off more bits of residuals for lower
Expand All @@ -476,7 +544,7 @@ int VP8LResidualImage(int width, int height, int bits, int low_effort,
uint32_t* const image, int near_lossless_quality,
int exact, int used_subtract_green,
const WebPPicture* const pic, int percent_range,
int* const percent) {
int* const percent, int* const best_bits) {
const int tiles_per_row = VP8LSubSampleSize(width, bits);
const int tiles_per_col = VP8LSubSampleSize(height, bits);
int percent_start = *percent;
Expand All @@ -486,6 +554,7 @@ int VP8LResidualImage(int width, int height, int bits, int low_effort,
for (i = 0; i < tiles_per_row * tiles_per_col; ++i) {
image[i] = ARGB_BLACK | (kPredLowEffort << 8);
}
*best_bits = bits;
} else {
int tile_y;
uint32_t histo[HISTO_SIZE] = { 0 };
Expand All @@ -504,9 +573,10 @@ int VP8LResidualImage(int width, int height, int bits, int low_effort,
return 0;
}
}
OptimizeSampling(image, width, height, bits, best_bits);
}

CopyImageWithPrediction(width, height, bits, image, argb_scratch, argb,
CopyImageWithPrediction(width, height, *best_bits, image, argb_scratch, argb,
low_effort, max_quantization, exact,
used_subtract_green);
return WebPReportProgress(pic, percent_start + percent_range, percent);
Expand Down Expand Up @@ -724,7 +794,7 @@ static void CopyTileWithColorTransform(int xsize, int ysize,
int VP8LColorSpaceTransform(int width, int height, int bits, int quality,
uint32_t* const argb, uint32_t* image,
const WebPPicture* const pic, int percent_range,
int* const percent) {
int* const percent, int* best_bits) {
const int max_tile_size = 1 << bits;
const int tile_xsize = VP8LSubSampleSize(width, bits);
const int tile_ysize = VP8LSubSampleSize(height, bits);
Expand Down Expand Up @@ -784,5 +854,6 @@ int VP8LColorSpaceTransform(int width, int height, int bits, int quality,
return 0;
}
}
OptimizeSampling(image, width, height, bits, best_bits);
return 1;
}
45 changes: 22 additions & 23 deletions src/enc/vp8l_enc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1071,26 +1071,27 @@ static int ApplyPredictFilter(VP8LEncoder* const enc, int width, int height,
int quality, int low_effort,
int used_subtract_green, VP8LBitWriter* const bw,
int percent_range, int* const percent) {
const int pred_bits = enc->predictor_transform_bits_;
const int transform_width = VP8LSubSampleSize(width, pred_bits);
const int transform_height = VP8LSubSampleSize(height, pred_bits);
const int min_bits = enc->predictor_transform_bits_;
int best_bits;
// we disable near-lossless quantization if palette is used.
const int near_lossless_strength =
enc->use_palette_ ? 100 : enc->config_->near_lossless;

if (!VP8LResidualImage(
width, height, pred_bits, low_effort, enc->argb_, enc->argb_scratch_,
enc->transform_data_, near_lossless_strength, enc->config_->exact,
used_subtract_green, enc->pic_, percent_range / 2, percent)) {
if (!VP8LResidualImage(width, height, min_bits, low_effort, enc->argb_,
enc->argb_scratch_, enc->transform_data_,
near_lossless_strength, enc->config_->exact,
used_subtract_green, enc->pic_, percent_range / 2,
percent, &best_bits)) {
return 0;
}
VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
VP8LPutBits(bw, PREDICTOR_TRANSFORM, 2);
assert(pred_bits >= MIN_TRANSFORM_BITS && pred_bits <= MAX_TRANSFORM_BITS);
VP8LPutBits(bw, pred_bits - MIN_TRANSFORM_BITS, NUM_TRANSFORM_BITS);
assert(best_bits >= MIN_TRANSFORM_BITS && best_bits <= MAX_TRANSFORM_BITS);
VP8LPutBits(bw, best_bits - MIN_TRANSFORM_BITS, NUM_TRANSFORM_BITS);
enc->predictor_transform_bits_ = best_bits;
return EncodeImageNoHuffman(
bw, enc->transform_data_, (VP8LHashChain*)&enc->hash_chain_,
(VP8LBackwardRefs*)&enc->refs_[0], transform_width, transform_height,
bw, enc->transform_data_, &enc->hash_chain_, &enc->refs_[0],
VP8LSubSampleSize(width, best_bits), VP8LSubSampleSize(height, best_bits),
quality, low_effort, enc->pic_, percent_range - percent_range / 2,
percent);
}
Expand All @@ -1099,24 +1100,22 @@ static int ApplyCrossColorFilter(VP8LEncoder* const enc, int width, int height,
int quality, int low_effort,
VP8LBitWriter* const bw, int percent_range,
int* const percent) {
const int ccolor_transform_bits = enc->cross_color_transform_bits_;
const int transform_width = VP8LSubSampleSize(width, ccolor_transform_bits);
const int transform_height = VP8LSubSampleSize(height, ccolor_transform_bits);
const int min_bits = enc->cross_color_transform_bits_;
int best_bits;

if (!VP8LColorSpaceTransform(width, height, ccolor_transform_bits, quality,
enc->argb_, enc->transform_data_, enc->pic_,
percent_range / 2, percent)) {
if (!VP8LColorSpaceTransform(width, height, min_bits, quality, enc->argb_,
enc->transform_data_, enc->pic_,
percent_range / 2, percent, &best_bits)) {
return 0;
}
VP8LPutBits(bw, TRANSFORM_PRESENT, 1);
VP8LPutBits(bw, CROSS_COLOR_TRANSFORM, 2);
assert(ccolor_transform_bits >= MIN_TRANSFORM_BITS &&
ccolor_transform_bits <= MAX_TRANSFORM_BITS);
VP8LPutBits(bw, ccolor_transform_bits - MIN_TRANSFORM_BITS,
NUM_TRANSFORM_BITS);
assert(best_bits >= MIN_TRANSFORM_BITS && best_bits <= MAX_TRANSFORM_BITS);
VP8LPutBits(bw, best_bits - MIN_TRANSFORM_BITS, NUM_TRANSFORM_BITS);
enc->cross_color_transform_bits_ = best_bits;
return EncodeImageNoHuffman(
bw, enc->transform_data_, (VP8LHashChain*)&enc->hash_chain_,
(VP8LBackwardRefs*)&enc->refs_[0], transform_width, transform_height,
bw, enc->transform_data_, &enc->hash_chain_, &enc->refs_[0],
VP8LSubSampleSize(width, best_bits), VP8LSubSampleSize(height, best_bits),
quality, low_effort, enc->pic_, percent_range - percent_range / 2,
percent);
}
Expand Down
4 changes: 2 additions & 2 deletions src/enc/vp8li_enc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -110,12 +110,12 @@ int VP8LResidualImage(int width, int height, int bits, int low_effort,
uint32_t* const image, int near_lossless_quality,
int exact, int used_subtract_green,
const WebPPicture* const pic, int percent_range,
int* const percent);
int* const percent, int* const best_bits);

int VP8LColorSpaceTransform(int width, int height, int bits, int quality,
uint32_t* const argb, uint32_t* image,
const WebPPicture* const pic, int percent_range,
int* const percent);
int* const percent, int* const best_bits);

//------------------------------------------------------------------------------

Expand Down

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