generic-library/webp
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Merge "speed-up lossless (~3%) with ad-hoc histogram cost evaluation" into 0.3.0

Browse Source
This commit is contained in:
James Zern 2013-03-18 17:48:59 -07:00 committed by Gerrit Code Review
commit 401f7b856f
3 changed files with 159 additions and 76 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

211
src/enc/histogram.c
View File

@ -98,8 +98,6 @@ void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo,
}
}
static double BitsEntropy(const int* const array, int n) {
double retval = 0.;
int sum = 0;
@ -149,25 +147,6 @@ static double BitsEntropy(const int* const array, int n) {
}
}
double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p) {
double retval = BitsEntropy(&p->literal_[0], VP8LHistogramNumCodes(p))
+ BitsEntropy(&p->red_[0], 256)
+ BitsEntropy(&p->blue_[0], 256)
+ BitsEntropy(&p->alpha_[0], 256)
+ BitsEntropy(&p->distance_[0], NUM_DISTANCE_CODES);
// Compute the extra bits cost.
int i;
for (i = 2; i < NUM_LENGTH_CODES - 2; ++i) {
retval +=
(i >> 1) * p->literal_[256 + i + 2];
}
for (i = 2; i < NUM_DISTANCE_CODES - 2; ++i) {
retval += (i >> 1) * p->distance_[i + 2];
}
return retval;
}
// Returns the cost encode the rle-encoded entropy code.
// The constants in this function are experimental.
static double HuffmanCost(const int* const population, int length) {
@ -207,19 +186,150 @@ static double HuffmanCost(const int* const population, int length) {
return retval;
}
// Estimates the Huffman dictionary + other block overhead size.
static double HistogramEstimateBitsHeader(const VP8LHistogram* const p) {
return HuffmanCost(&p->alpha_[0], 256) +
HuffmanCost(&p->red_[0], 256) +
HuffmanCost(&p->literal_[0], VP8LHistogramNumCodes(p)) +
HuffmanCost(&p->blue_[0], 256) +
HuffmanCost(&p->distance_[0], NUM_DISTANCE_CODES);
static double PopulationCost(const int* const population, int length) {
return BitsEntropy(population, length) + HuffmanCost(population, length);
}
double VP8LHistogramEstimateBits(const VP8LHistogram* const p) {
return HistogramEstimateBitsHeader(p) + VP8LHistogramEstimateBitsBulk(p);
static double ExtraCost(const int* const population, int length) {
int i;
double cost = 0.;
for (i = 2; i < length - 2; ++i) cost += (i >> 1) * population[i + 2];
return cost;
}
// Estimates the Entropy + Huffman + other block overhead size cost.
double VP8LHistogramEstimateBits(const VP8LHistogram* const p) {
return PopulationCost(p->literal_, VP8LHistogramNumCodes(p))
+ PopulationCost(p->red_, 256)
+ PopulationCost(p->blue_, 256)
+ PopulationCost(p->alpha_, 256)
+ PopulationCost(p->distance_, NUM_DISTANCE_CODES)
+ ExtraCost(p->literal_ + 256, NUM_LENGTH_CODES)
+ ExtraCost(p->distance_, NUM_DISTANCE_CODES);
}
double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p) {
return BitsEntropy(p->literal_, VP8LHistogramNumCodes(p))
+ BitsEntropy(p->red_, 256)
+ BitsEntropy(p->blue_, 256)
+ BitsEntropy(p->alpha_, 256)
+ BitsEntropy(p->distance_, NUM_DISTANCE_CODES)
+ ExtraCost(p->literal_ + 256, NUM_LENGTH_CODES)
+ ExtraCost(p->distance_, NUM_DISTANCE_CODES);
}
// -----------------------------------------------------------------------------
// Various histogram combine/cost-eval functions
// Adds 'in' histogram to 'out'
static void HistogramAdd(const VP8LHistogram* const in,
VP8LHistogram* const out) {
int i;
for (i = 0; i < PIX_OR_COPY_CODES_MAX; ++i) {
out->literal_[i] += in->literal_[i];
}
for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
out->distance_[i] += in->distance_[i];
}
for (i = 0; i < 256; ++i) {
out->red_[i] += in->red_[i];
out->blue_[i] += in->blue_[i];
out->alpha_[i] += in->alpha_[i];
}
}
// Performs out = a + b, computing the cost C(a+b) - C(a) - C(b) while comparing
// to the threshold value 'cost_threshold'. The score returned is
// Score = C(a+b) - C(a) - C(b), where C(a) + C(b) is known and fixed.
// Since the previous score passed is 'cost_threshold', we only need to compare
// the partial cost against 'cost_threshold + C(a) + C(b)' to possibly bail-out
// early.
static double HistogramAddEval(const VP8LHistogram* const a,
const VP8LHistogram* const b,
VP8LHistogram* const out,
double cost_threshold) {
double cost = 0;
const double sum_cost = a->bit_cost_ + b->bit_cost_;
int i;
cost_threshold += sum_cost;
// palette_code_bits_ is part of the cost evaluation for literal_.
// TODO(skal): remove/simplify this palette_code_bits_?
out->palette_code_bits_ =
(a->palette_code_bits_ > b->palette_code_bits_) ? a->palette_code_bits_ :
b->palette_code_bits_;
for (i = 0; i < PIX_OR_COPY_CODES_MAX; ++i) {
out->literal_[i] = a->literal_[i] + b->literal_[i];
}
cost += PopulationCost(out->literal_, VP8LHistogramNumCodes(out));
cost += ExtraCost(out->literal_ + 256, NUM_LENGTH_CODES);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) out->red_[i] = a->red_[i] + b->red_[i];
cost += PopulationCost(out->red_, 256);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) out->blue_[i] = a->blue_[i] + b->blue_[i];
cost += PopulationCost(out->blue_, 256);
if (cost > cost_threshold) return cost;
for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
out->distance_[i] = a->distance_[i] + b->distance_[i];
}
cost += PopulationCost(out->distance_, NUM_DISTANCE_CODES);
cost += ExtraCost(out->distance_, NUM_DISTANCE_CODES);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) out->alpha_[i] = a->alpha_[i] + b->alpha_[i];
cost += PopulationCost(out->alpha_, 256);
out->bit_cost_ = cost;
return cost - sum_cost;
}
// Same as HistogramAddEval(), except that the resulting histogram
// is not stored. Only the cost C(a+b) - C(a) is evaluated. We omit
// the term C(b) which is constant over all the evaluations.
static double HistogramAddThresh(const VP8LHistogram* const a,
const VP8LHistogram* const b,
double cost_threshold) {
int tmp[PIX_OR_COPY_CODES_MAX]; // <= max storage we'll need
int i;
double cost = -a->bit_cost_;
for (i = 0; i < PIX_OR_COPY_CODES_MAX; ++i) {
tmp[i] = a->literal_[i] + b->literal_[i];
}
// note that the tests are ordered so that the usually largest
// cost shares come first.
cost += PopulationCost(tmp, VP8LHistogramNumCodes(a));
cost += ExtraCost(tmp + 256, NUM_LENGTH_CODES);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) tmp[i] = a->red_[i] + b->red_[i];
cost += PopulationCost(tmp, 256);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) tmp[i] = a->blue_[i] + b->blue_[i];
cost += PopulationCost(tmp, 256);
if (cost > cost_threshold) return cost;
for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
tmp[i] = a->distance_[i] + b->distance_[i];
}
cost += PopulationCost(tmp, NUM_DISTANCE_CODES);
cost += ExtraCost(tmp, NUM_DISTANCE_CODES);
if (cost > cost_threshold) return cost;
for (i = 0; i < 256; ++i) tmp[i] = a->alpha_[i] + b->alpha_[i];
cost += PopulationCost(tmp, 256);
return cost;
}
// -----------------------------------------------------------------------------
static void HistogramBuildImage(int xsize, int histo_bits,
const VP8LBackwardRefs* const backward_refs,
VP8LHistogramSet* const image) {
@ -273,7 +383,7 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
// Collapse similar histograms in 'out'.
for (iter = 0; iter < outer_iters && out_size >= min_cluster_size; ++iter) {
double best_cost_diff = 0.;
int best_idx1 = 0, best_idx2 = 1;
int best_idx1 = -1, best_idx2 = 1;
int j;
const int num_tries = (num_pairs < out_size) ? num_pairs : out_size;
seed += iter;
@ -281,20 +391,17 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
double curr_cost_diff;
// Choose two histograms at random and try to combine them.
const uint32_t idx1 = MyRand(&seed) % out_size;
const uint32_t tmp = ((j & 7) + 1) % (out_size - 1);
const uint32_t tmp = (j & 7) + 1;
const uint32_t diff = (tmp < 3) ? tmp : MyRand(&seed) % (out_size - 1);
const uint32_t idx2 = (idx1 + diff + 1) % out_size;
if (idx1 == idx2) {
continue;
}
*cur_combo = *out->histograms[idx1];
VP8LHistogramAdd(cur_combo, out->histograms[idx2]);
cur_combo->bit_cost_ = VP8LHistogramEstimateBits(cur_combo);
// Calculate cost reduction on combining.
curr_cost_diff = cur_combo->bit_cost_
- out->histograms[idx1]->bit_cost_
- out->histograms[idx2]->bit_cost_;
if (best_cost_diff > curr_cost_diff) { // found a better pair?
curr_cost_diff = HistogramAddEval(out->histograms[idx1],
out->histograms[idx2],
cur_combo, best_cost_diff);
if (curr_cost_diff < best_cost_diff) { // found a better pair?
{ // swap cur/best combo histograms
VP8LHistogram* const tmp_histo = cur_combo;
cur_combo = best_combo;
@ -306,7 +413,7 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
}
}
if (best_cost_diff < 0.0) {
if (best_idx1 >= 0) {
*out->histograms[best_idx1] = *best_combo;
// swap best_idx2 slot with last one (which is now unused)
--out_size;
@ -331,20 +438,11 @@ static int HistogramCombine(const VP8LHistogramSet* const in,
// -----------------------------------------------------------------------------
// Histogram refinement
// What is the bit cost of moving square_histogram from
// cur_symbol to candidate_symbol.
// TODO(skal): we don't really need to copy the histogram and Add(). Instead
// we just need VP8LDualHistogramEstimateBits(A, B) estimation function.
// What is the bit cost of moving square_histogram from cur_symbol to candidate.
static double HistogramDistance(const VP8LHistogram* const square_histogram,
const VP8LHistogram* const candidate) {
const double previous_bit_cost = candidate->bit_cost_;
double new_bit_cost;
VP8LHistogram modified_histo;
modified_histo = *candidate;
VP8LHistogramAdd(&modified_histo, square_histogram);
new_bit_cost = VP8LHistogramEstimateBits(&modified_histo);
return new_bit_cost - previous_bit_cost;
const VP8LHistogram* const candidate,
double cost_threshold) {
return HistogramAddThresh(candidate, square_histogram, cost_threshold);
}
// Find the best 'out' histogram for each of the 'in' histograms.
@ -355,11 +453,12 @@ static void HistogramRemap(const VP8LHistogramSet* const in,
int i;
for (i = 0; i < in->size; ++i) {
int best_out = 0;
double best_bits = HistogramDistance(in->histograms[i], out->histograms[0]);
double best_bits =
HistogramDistance(in->histograms[i], out->histograms[0], 1.e38);
int k;
for (k = 1; k < out->size; ++k) {
const double cur_bits =
HistogramDistance(in->histograms[i], out->histograms[k]);
HistogramDistance(in->histograms[i], out->histograms[k], best_bits);
if (cur_bits < best_bits) {
best_bits = cur_bits;
best_out = k;
@ -373,7 +472,7 @@ static void HistogramRemap(const VP8LHistogramSet* const in,
HistogramClear(out->histograms[i]);
}
for (i = 0; i < in->size; ++i) {
VP8LHistogramAdd(out->histograms[symbols[i]], in->histograms[i]);
HistogramAdd(in->histograms[i], out->histograms[symbols[i]]);
}
}

16
src/enc/histogram.h
View File

@ -80,22 +80,6 @@ double VP8LHistogramEstimateBits(const VP8LHistogram* const p);
// represent the entropy code itself.
double VP8LHistogramEstimateBitsBulk(const VP8LHistogram* const p);
static WEBP_INLINE void VP8LHistogramAdd(VP8LHistogram* const p,
const VP8LHistogram* const a) {
int i;
for (i = 0; i < PIX_OR_COPY_CODES_MAX; ++i) {
p->literal_[i] += a->literal_[i];
}
for (i = 0; i < NUM_DISTANCE_CODES; ++i) {
p->distance_[i] += a->distance_[i];
}
for (i = 0; i < 256; ++i) {
p->red_[i] += a->red_[i];
p->blue_[i] += a->blue_[i];
p->alpha_[i] += a->alpha_[i];
}
}
static WEBP_INLINE int VP8LHistogramNumCodes(const VP8LHistogram* const p) {
return 256 + NUM_LENGTH_CODES +
((p->palette_code_bits_ > 0) ? (1 << p->palette_code_bits_) : 0);

8
src/enc/vp8l.c
View File

@ -563,6 +563,9 @@ static int EncodeImageInternal(VP8LBitWriter* const bw,
!GetHuffBitLengthsAndCodes(histogram_image, huffman_codes)) {
goto Error;
}
// Free combined histograms.
free(histogram_image);
histogram_image = NULL;
// Color Cache parameters.
VP8LWriteBits(bw, 1, use_color_cache);
@ -609,9 +612,6 @@ static int EncodeImageInternal(VP8LBitWriter* const bw,
ClearHuffmanTreeIfOnlyOneSymbol(codes);
}
}
// Free combined histograms.
free(histogram_image);
histogram_image = NULL;
// Store actual literals.
StoreImageToBitMask(bw, width, histogram_bits, &refs,
@ -619,7 +619,7 @@ static int EncodeImageInternal(VP8LBitWriter* const bw,
ok = 1;
Error:
if (!ok) free(histogram_image);
free(histogram_image);
VP8LClearBackwardRefs(&refs);
if (huffman_codes != NULL) {