// Copyright 2012 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. // ----------------------------------------------------------------------------- // // Author: Jyrki Alakuijala (jyrki@google.com) // #ifdef HAVE_CONFIG_H #include "webp/config.h" #endif #include #include "./backward_references.h" #include "./histogram.h" #include "../dsp/lossless.h" #include "../utils/utils.h" #define MAX_COST 1.e38 // Number of partitions for the three dominant (literal, red and blue) symbol // costs. #define NUM_PARTITIONS 4 // The size of the bin-hash corresponding to the three dominant costs. #define BIN_SIZE (NUM_PARTITIONS * NUM_PARTITIONS * NUM_PARTITIONS) // Maximum number of histograms allowed in greedy combining algorithm. #define MAX_HISTO_GREEDY 100 static void HistogramClear(VP8LHistogram* const p) { uint32_t* const literal = p->literal_; const int cache_bits = p->palette_code_bits_; const int histo_size = VP8LGetHistogramSize(cache_bits); memset(p, 0, histo_size); p->palette_code_bits_ = cache_bits; p->literal_ = literal; } // Swap two histogram pointers. static void HistogramSwap(VP8LHistogram** const A, VP8LHistogram** const B) { VP8LHistogram* const tmp = *A; *A = *B; *B = tmp; } static void HistogramCopy(const VP8LHistogram* const src, VP8LHistogram* const dst) { uint32_t* const dst_literal = dst->literal_; const int dst_cache_bits = dst->palette_code_bits_; const int histo_size = VP8LGetHistogramSize(dst_cache_bits); assert(src->palette_code_bits_ == dst_cache_bits); memcpy(dst, src, histo_size); dst->literal_ = dst_literal; } int VP8LGetHistogramSize(int cache_bits) { const int literal_size = VP8LHistogramNumCodes(cache_bits); const size_t total_size = sizeof(VP8LHistogram) + sizeof(int) * literal_size; assert(total_size <= (size_t)0x7fffffff); return (int)total_size; } void VP8LFreeHistogram(VP8LHistogram* const histo) { WebPSafeFree(histo); } void VP8LFreeHistogramSet(VP8LHistogramSet* const histo) { WebPSafeFree(histo); } void VP8LHistogramStoreRefs(const VP8LBackwardRefs* const refs, VP8LHistogram* const histo) { VP8LRefsCursor c = VP8LRefsCursorInit(refs); while (VP8LRefsCursorOk(&c)) { VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos); VP8LRefsCursorNext(&c); } } void VP8LHistogramCreate(VP8LHistogram* const p, const VP8LBackwardRefs* const refs, int palette_code_bits) { if (palette_code_bits >= 0) { p->palette_code_bits_ = palette_code_bits; } HistogramClear(p); VP8LHistogramStoreRefs(refs, p); } void VP8LHistogramInit(VP8LHistogram* const p, int palette_code_bits) { p->palette_code_bits_ = palette_code_bits; HistogramClear(p); } VP8LHistogram* VP8LAllocateHistogram(int cache_bits) { VP8LHistogram* histo = NULL; const int total_size = VP8LGetHistogramSize(cache_bits); uint8_t* const memory = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*memory)); if (memory == NULL) return NULL; histo = (VP8LHistogram*)memory; // literal_ won't necessary be aligned. histo->literal_ = (uint32_t*)(memory + sizeof(VP8LHistogram)); VP8LHistogramInit(histo, cache_bits); return histo; } VP8LHistogramSet* VP8LAllocateHistogramSet(int size, int cache_bits) { int i; VP8LHistogramSet* set; const int histo_size = VP8LGetHistogramSize(cache_bits); const size_t total_size = sizeof(*set) + size * (sizeof(*set->histograms) + histo_size + WEBP_ALIGN_CST); uint8_t* memory = (uint8_t*)WebPSafeMalloc(total_size, sizeof(*memory)); if (memory == NULL) return NULL; set = (VP8LHistogramSet*)memory; memory += sizeof(*set); set->histograms = (VP8LHistogram**)memory; memory += size * sizeof(*set->histograms); set->max_size = size; set->size = size; for (i = 0; i < size; ++i) { memory = (uint8_t*)WEBP_ALIGN(memory); set->histograms[i] = (VP8LHistogram*)memory; // literal_ won't necessary be aligned. set->histograms[i]->literal_ = (uint32_t*)(memory + sizeof(VP8LHistogram)); VP8LHistogramInit(set->histograms[i], cache_bits); memory += histo_size; } return set; } // ----------------------------------------------------------------------------- void VP8LHistogramAddSinglePixOrCopy(VP8LHistogram* const histo, const PixOrCopy* const v) { if (PixOrCopyIsLiteral(v)) { ++histo->alpha_[PixOrCopyLiteral(v, 3)]; ++histo->red_[PixOrCopyLiteral(v, 2)]; ++histo->literal_[PixOrCopyLiteral(v, 1)]; ++histo->blue_[PixOrCopyLiteral(v, 0)]; } else if (PixOrCopyIsCacheIdx(v)) { const int literal_ix = NUM_LITERAL_CODES + NUM_LENGTH_CODES + PixOrCopyCacheIdx(v); ++histo->literal_[literal_ix]; } else { int code, extra_bits; VP8LPrefixEncodeBits(PixOrCopyLength(v), &code, &extra_bits); ++histo->literal_[NUM_LITERAL_CODES + code]; VP8LPrefixEncodeBits(PixOrCopyDistance(v), &code, &extra_bits); ++histo->distance_[code]; } } // ----------------------------------------------------------------------------- // Various histogram combine/cost-eval functions static int GetCombinedHistogramEntropy(const VP8LHistogram* const a, const VP8LHistogram* const b, double cost_threshold, double* cost) { const int palette_code_bits = a->palette_code_bits_; assert(a->palette_code_bits_ == b->palette_code_bits_); *cost += VP8LGetCombinedEntropy(a->literal_, b->literal_, VP8LHistogramNumCodes(palette_code_bits)); *cost += VP8LExtraCostCombined(a->literal_ + NUM_LITERAL_CODES, b->literal_ + NUM_LITERAL_CODES, NUM_LENGTH_CODES); if (*cost > cost_threshold) return 0; *cost += VP8LGetCombinedEntropy(a->red_, b->red_, NUM_LITERAL_CODES); if (*cost > cost_threshold) return 0; *cost += VP8LGetCombinedEntropy(a->blue_, b->blue_, NUM_LITERAL_CODES); if (*cost > cost_threshold) return 0; *cost += VP8LGetCombinedEntropy(a->alpha_, b->alpha_, NUM_LITERAL_CODES); if (*cost > cost_threshold) return 0; *cost += VP8LGetCombinedEntropy(a->distance_, b->distance_, NUM_DISTANCE_CODES); *cost += VP8LExtraCostCombined(a->distance_, b->distance_, NUM_DISTANCE_CODES); if (*cost > cost_threshold) return 0; return 1; } // 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_; cost_threshold += sum_cost; if (GetCombinedHistogramEntropy(a, b, cost_threshold, &cost)) { VP8LHistogramAdd(a, b, out); out->bit_cost_ = cost; out->palette_code_bits_ = a->palette_code_bits_; out->trivial_symbol_ = (a->trivial_symbol_ == b->trivial_symbol_) ? a->trivial_symbol_ : VP8L_NON_TRIVIAL_SYM; } 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) { double cost = -a->bit_cost_; GetCombinedHistogramEntropy(a, b, cost_threshold, &cost); return cost; } // ----------------------------------------------------------------------------- // The structure to keep track of cost range for the three dominant entropy // symbols. // TODO(skal): Evaluate if float can be used here instead of double for // representing the entropy costs. typedef struct { double literal_max_; double literal_min_; double red_max_; double red_min_; double blue_max_; double blue_min_; } DominantCostRange; static void DominantCostRangeInit(DominantCostRange* const c) { c->literal_max_ = 0.; c->literal_min_ = MAX_COST; c->red_max_ = 0.; c->red_min_ = MAX_COST; c->blue_max_ = 0.; c->blue_min_ = MAX_COST; } static void UpdateDominantCostRange( const VP8LHistogram* const h, DominantCostRange* const c) { if (c->literal_max_ < h->literal_cost_) c->literal_max_ = h->literal_cost_; if (c->literal_min_ > h->literal_cost_) c->literal_min_ = h->literal_cost_; if (c->red_max_ < h->red_cost_) c->red_max_ = h->red_cost_; if (c->red_min_ > h->red_cost_) c->red_min_ = h->red_cost_; if (c->blue_max_ < h->blue_cost_) c->blue_max_ = h->blue_cost_; if (c->blue_min_ > h->blue_cost_) c->blue_min_ = h->blue_cost_; } static void UpdateHistogramCost(VP8LHistogram* const h) { uint32_t alpha_sym, red_sym, blue_sym; const double alpha_cost = VP8LPopulationCost(h->alpha_, NUM_LITERAL_CODES, &alpha_sym); const double distance_cost = VP8LPopulationCost(h->distance_, NUM_DISTANCE_CODES, NULL) + VP8LExtraCost(h->distance_, NUM_DISTANCE_CODES); const int num_codes = VP8LHistogramNumCodes(h->palette_code_bits_); h->literal_cost_ = VP8LPopulationCost(h->literal_, num_codes, NULL) + VP8LExtraCost(h->literal_ + NUM_LITERAL_CODES, NUM_LENGTH_CODES); h->red_cost_ = VP8LPopulationCost(h->red_, NUM_LITERAL_CODES, &red_sym); h->blue_cost_ = VP8LPopulationCost(h->blue_, NUM_LITERAL_CODES, &blue_sym); h->bit_cost_ = h->literal_cost_ + h->red_cost_ + h->blue_cost_ + alpha_cost + distance_cost; if ((alpha_sym | red_sym | blue_sym) == VP8L_NON_TRIVIAL_SYM) { h->trivial_symbol_ = VP8L_NON_TRIVIAL_SYM; } else { h->trivial_symbol_ = ((uint32_t)alpha_sym << 24) | (red_sym << 16) | (blue_sym << 0); } } static int GetBinIdForEntropy(double min, double max, double val) { const double range = max - min + 1e-6; const double delta = val - min; return (int)(NUM_PARTITIONS * delta / range); } static int GetHistoBinIndexLowEffort( const VP8LHistogram* const h, const DominantCostRange* const c) { const int bin_id = GetBinIdForEntropy(c->literal_min_, c->literal_max_, h->literal_cost_); assert(bin_id < NUM_PARTITIONS); return bin_id; } static int GetHistoBinIndex( const VP8LHistogram* const h, const DominantCostRange* const c) { const int bin_id = GetBinIdForEntropy(c->blue_min_, c->blue_max_, h->blue_cost_) + NUM_PARTITIONS * GetBinIdForEntropy(c->red_min_, c->red_max_, h->red_cost_) + NUM_PARTITIONS * NUM_PARTITIONS * GetBinIdForEntropy(c->literal_min_, c->literal_max_, h->literal_cost_); assert(bin_id < BIN_SIZE); return bin_id; } // Construct the histograms from backward references. static void HistogramBuild( int xsize, int histo_bits, const VP8LBackwardRefs* const backward_refs, VP8LHistogramSet* const image_histo) { int x = 0, y = 0; const int histo_xsize = VP8LSubSampleSize(xsize, histo_bits); VP8LHistogram** const histograms = image_histo->histograms; VP8LRefsCursor c = VP8LRefsCursorInit(backward_refs); assert(histo_bits > 0); while (VP8LRefsCursorOk(&c)) { const PixOrCopy* const v = c.cur_pos; const int ix = (y >> histo_bits) * histo_xsize + (x >> histo_bits); VP8LHistogramAddSinglePixOrCopy(histograms[ix], v); x += PixOrCopyLength(v); while (x >= xsize) { x -= xsize; ++y; } VP8LRefsCursorNext(&c); } } // Copies the histograms and computes its bit_cost. static void HistogramCopyAndAnalyze( VP8LHistogramSet* const orig_histo, VP8LHistogramSet* const image_histo) { int i; const int histo_size = orig_histo->size; VP8LHistogram** const orig_histograms = orig_histo->histograms; VP8LHistogram** const histograms = image_histo->histograms; for (i = 0; i < histo_size; ++i) { VP8LHistogram* const histo = orig_histograms[i]; UpdateHistogramCost(histo); // Copy histograms from orig_histo[] to image_histo[]. HistogramCopy(histo, histograms[i]); } } // Partition histograms to different entropy bins for three dominant (literal, // red and blue) symbol costs and compute the histogram aggregate bit_cost. static void HistogramAnalyzeEntropyBin(VP8LHistogramSet* const image_histo, int16_t* const bin_map, int low_effort) { int i; VP8LHistogram** const histograms = image_histo->histograms; const int histo_size = image_histo->size; const int bin_depth = histo_size + 1; DominantCostRange cost_range; DominantCostRangeInit(&cost_range); // Analyze the dominant (literal, red and blue) entropy costs. for (i = 0; i < histo_size; ++i) { VP8LHistogram* const histo = histograms[i]; UpdateDominantCostRange(histo, &cost_range); } // bin-hash histograms on three of the dominant (literal, red and blue) // symbol costs. for (i = 0; i < histo_size; ++i) { int num_histos; VP8LHistogram* const histo = histograms[i]; const int16_t bin_id = low_effort ? (int16_t)GetHistoBinIndexLowEffort(histo, &cost_range) : (int16_t)GetHistoBinIndex(histo, &cost_range); const int bin_offset = bin_id * bin_depth; // bin_map[n][0] for every bin 'n' maintains the counter for the number of // histograms in that bin. // Get and increment the num_histos in that bin. num_histos = ++bin_map[bin_offset]; assert(bin_offset + num_histos < bin_depth * BIN_SIZE); // Add histogram i'th index at num_histos (last) position in the bin_map. bin_map[bin_offset + num_histos] = i; } } // Compact the histogram set by removing unused entries. static void HistogramCompactBins(VP8LHistogramSet* const image_histo) { VP8LHistogram** const histograms = image_histo->histograms; int i, j; for (i = 0, j = 0; i < image_histo->size; ++i) { if (histograms[i] != NULL && histograms[i]->bit_cost_ != 0.) { if (j < i) { histograms[j] = histograms[i]; histograms[i] = NULL; } ++j; } } image_histo->size = j; } static VP8LHistogram* HistogramCombineEntropyBin( VP8LHistogramSet* const image_histo, VP8LHistogram* cur_combo, int16_t* const bin_map, int bin_depth, int num_bins, double combine_cost_factor, int low_effort) { int bin_id; VP8LHistogram** const histograms = image_histo->histograms; for (bin_id = 0; bin_id < num_bins; ++bin_id) { const int bin_offset = bin_id * bin_depth; const int num_histos = bin_map[bin_offset]; const int idx1 = bin_map[bin_offset + 1]; int num_combine_failures = 0; int n; for (n = 2; n <= num_histos; ++n) { const int idx2 = bin_map[bin_offset + n]; if (low_effort) { // Merge all histograms with the same bin index, irrespective of cost of // the merged histograms. VP8LHistogramAdd(histograms[idx1], histograms[idx2], histograms[idx1]); histograms[idx2]->bit_cost_ = 0.; } else { const double bit_cost_idx2 = histograms[idx2]->bit_cost_; if (bit_cost_idx2 > 0.) { const double bit_cost_thresh = -bit_cost_idx2 * combine_cost_factor; const double curr_cost_diff = HistogramAddEval(histograms[idx1], histograms[idx2], cur_combo, bit_cost_thresh); if (curr_cost_diff < bit_cost_thresh) { // Try to merge two histograms only if the combo is a trivial one or // the two candidate histograms are already non-trivial. // For some images, 'try_combine' turns out to be false for a lot of // histogram pairs. In that case, we fallback to combining // histograms as usual to avoid increasing the header size. const int try_combine = (cur_combo->trivial_symbol_ != VP8L_NON_TRIVIAL_SYM) || ((histograms[idx1]->trivial_symbol_ == VP8L_NON_TRIVIAL_SYM) && (histograms[idx2]->trivial_symbol_ == VP8L_NON_TRIVIAL_SYM)); const int max_combine_failures = 32; if (try_combine || (num_combine_failures >= max_combine_failures)) { HistogramSwap(&cur_combo, &histograms[idx1]); histograms[idx2]->bit_cost_ = 0.; } else { ++num_combine_failures; } } } } } if (low_effort) { // Update the bit_cost for the merged histograms (per bin index). UpdateHistogramCost(histograms[idx1]); } } HistogramCompactBins(image_histo); return cur_combo; } static uint32_t MyRand(uint32_t *seed) { *seed *= 16807U; if (*seed == 0) { *seed = 1; } return *seed; } // ----------------------------------------------------------------------------- // Histogram pairs priority queue // Pair of histograms. Negative idx1 value means that pair is out-of-date. typedef struct { int idx1; int idx2; double cost_diff; double cost_combo; } HistogramPair; typedef struct { HistogramPair* heap; int* positions; int size; int max_index; } HistoHeap; static int HistoHeapInit(HistoHeap* const histo_heap, const int max_index) { histo_heap->size = 0; histo_heap->max_index = max_index; histo_heap->heap = WebPSafeMalloc(max_index * max_index, sizeof(*histo_heap->heap)); histo_heap->positions = WebPSafeMalloc(max_index * max_index, sizeof(*histo_heap->positions)); return histo_heap->heap != NULL && histo_heap->positions != NULL; } static void HistoHeapClear(HistoHeap* const histo_heap) { assert(histo_heap != NULL); WebPSafeFree(histo_heap->heap); WebPSafeFree(histo_heap->positions); } static void SwapHistogramPairs(HistogramPair *p1, HistogramPair *p2) { const HistogramPair tmp = *p1; *p1 = *p2; *p2 = tmp; } // Given a valid min-heap in range [0, heap_size-1) this function places value // heap[heap_size-1] into right location within heap and sets its position in // positions array. static void HeapPush(HistoHeap* const histo_heap) { HistogramPair* const heap = histo_heap->heap - 1; int* const positions = histo_heap->positions; const int max_index = histo_heap->max_index; int v; ++histo_heap->size; v = histo_heap->size; while (v > 1 && heap[v].cost_diff < heap[v >> 1].cost_diff) { SwapHistogramPairs(&heap[v], &heap[v >> 1]); // Change position of moved pair in heap. if (heap[v].idx1 >= 0) { const int pos = heap[v].idx1 * max_index + heap[v].idx2; assert(pos >= 0 && pos < max_index * max_index); positions[pos] = v; } v >>= 1; } positions[heap[v].idx1 * max_index + heap[v].idx2] = v; } // Given a valid min-heap in range [0, heap_size) this function shortens heap // range by one and places element with the lowest value to (heap_size-1). static void HeapPop(HistoHeap* const histo_heap) { HistogramPair* const heap = histo_heap->heap - 1; int* const positions = histo_heap->positions; const int heap_size = histo_heap->size; const int max_index = histo_heap->max_index; int v = 1; if (heap[v].idx1 >= 0) { positions[heap[v].idx1 * max_index + heap[v].idx2] = -1; } SwapHistogramPairs(&heap[v], &heap[heap_size]); while ((v << 1) < heap_size) { int son = (heap[v << 1].cost_diff < heap[v].cost_diff) ? (v << 1) : v; if (((v << 1) + 1) < heap_size && heap[(v << 1) + 1].cost_diff < heap[son].cost_diff) { son = (v << 1) + 1; } if (son == v) break; SwapHistogramPairs(&heap[v], &heap[son]); // Change position of moved pair in heap. if (heap[v].idx1 >= 0) { positions[heap[v].idx1 * max_index + heap[v].idx2] = v; } v = son; } if (heap[v].idx1 >= 0) { positions[heap[v].idx1 * max_index + heap[v].idx2] = v; } --histo_heap->size; } // ----------------------------------------------------------------------------- static void PreparePair(VP8LHistogram** histograms, int idx1, int idx2, HistogramPair* const pair, VP8LHistogram* const histos) { if (idx1 > idx2) { const int tmp = idx2; idx2 = idx1; idx1 = tmp; } pair->idx1 = idx1; pair->idx2 = idx2; pair->cost_diff = HistogramAddEval(histograms[idx1], histograms[idx2], histos, 0); pair->cost_combo = histos->bit_cost_; } #define POSITION_INVALID (-1) // Invalidates pairs intersecting (idx1, idx2) in heap. static void InvalidatePairs(int idx1, int idx2, const HistoHeap* const histo_heap) { HistogramPair* const heap = histo_heap->heap - 1; int* const positions = histo_heap->positions; const int max_index = histo_heap->max_index; int i; for (i = 0; i < idx1; ++i) { const int pos = positions[i * max_index + idx1]; if (pos >= 0) { heap[pos].idx1 = POSITION_INVALID; } } for (i = idx1 + 1; i < max_index; ++i) { const int pos = positions[idx1 * max_index + i]; if (pos >= 0) { heap[pos].idx1 = POSITION_INVALID; } } for (i = 0; i < idx2; ++i) { const int pos = positions[i * max_index + idx2]; if (pos >= 0) { heap[pos].idx1 = POSITION_INVALID; } } for (i = idx2 + 1; i < max_index; ++i) { const int pos = positions[idx2 * max_index + i]; if (pos >= 0) { heap[pos].idx1 = POSITION_INVALID; } } } // Combines histograms by continuously choosing the one with the highest cost // reduction. static int HistogramCombineGreedy(VP8LHistogramSet* const image_histo, VP8LHistogram* const histos) { int ok = 0; int image_histo_size = image_histo->size; int i, j; VP8LHistogram** const histograms = image_histo->histograms; // Indexes of remaining histograms. int* const clusters = WebPSafeMalloc(image_histo_size, sizeof(*clusters)); // Heap of histogram pairs. HistoHeap histo_heap; if (!HistoHeapInit(&histo_heap, image_histo_size) || clusters == NULL) { goto End; } for (i = 0; i < image_histo_size; ++i) { // Initialize clusters indexes. clusters[i] = i; for (j = i + 1; j < image_histo_size; ++j) { // Initialize positions array. histo_heap.positions[i * histo_heap.max_index + j] = POSITION_INVALID; PreparePair(histograms, i, j, &histo_heap.heap[histo_heap.size], histos); if (histo_heap.heap[histo_heap.size].cost_diff < 0) { HeapPush(&histo_heap); } } } while (image_histo_size > 1 && histo_heap.size > 0) { const int idx1 = histo_heap.heap[0].idx1; const int idx2 = histo_heap.heap[0].idx2; VP8LHistogramAdd(histograms[idx2], histograms[idx1], histograms[idx1]); histograms[idx1]->bit_cost_ = histo_heap.heap[0].cost_combo; // Remove merged histogram. for (i = 0; i + 1 < image_histo_size; ++i) { if (clusters[i] >= idx2) { clusters[i] = clusters[i + 1]; } } --image_histo_size; // Invalidate pairs intersecting the just combined best pair. InvalidatePairs(idx1, idx2, &histo_heap); // Pop invalid pairs from the top of the heap. while (histo_heap.size > 0 && histo_heap.heap[0].idx1 < 0) { HeapPop(&histo_heap); } // Push new pairs formed with combined histogram to the heap. for (i = 0; i < image_histo_size; ++i) { if (clusters[i] != idx1) { PreparePair(histograms, idx1, clusters[i], &histo_heap.heap[histo_heap.size], histos); if (histo_heap.heap[histo_heap.size].cost_diff < 0) { HeapPush(&histo_heap); } } } } // Move remaining histograms to the beginning of the array. for (i = 0; i < image_histo_size; ++i) { if (i != clusters[i]) { // swap the two histograms HistogramSwap(&histograms[i], &histograms[clusters[i]]); } } image_histo->size = image_histo_size; ok = 1; End: WebPSafeFree(clusters); HistoHeapClear(&histo_heap); return ok; } static VP8LHistogram* HistogramCombineStochastic( VP8LHistogramSet* const image_histo, VP8LHistogram* tmp_histo, VP8LHistogram* best_combo, int quality, int min_cluster_size) { int iter; uint32_t seed = 0; int tries_with_no_success = 0; int image_histo_size = image_histo->size; const int iter_mult = (quality < 25) ? 2 : 2 + (quality - 25) / 8; const int outer_iters = image_histo_size * iter_mult; const int num_pairs = image_histo_size / 2; const int num_tries_no_success = outer_iters / 2; VP8LHistogram** const histograms = image_histo->histograms; // Collapse similar histograms in 'image_histo'. ++min_cluster_size; for (iter = 0; iter < outer_iters && image_histo_size >= min_cluster_size; ++iter) { double best_cost_diff = 0.; int best_idx1 = -1, best_idx2 = 1; int j; const int num_tries = (num_pairs < image_histo_size) ? num_pairs : image_histo_size; seed += iter; for (j = 0; j < num_tries; ++j) { double curr_cost_diff; // Choose two histograms at random and try to combine them. const uint32_t idx1 = MyRand(&seed) % image_histo_size; const uint32_t tmp = (j & 7) + 1; const uint32_t diff = (tmp < 3) ? tmp : MyRand(&seed) % (image_histo_size - 1); const uint32_t idx2 = (idx1 + diff + 1) % image_histo_size; if (idx1 == idx2) { continue; } // Calculate cost reduction on combining. curr_cost_diff = HistogramAddEval(histograms[idx1], histograms[idx2], tmp_histo, best_cost_diff); if (curr_cost_diff < best_cost_diff) { // found a better pair? HistogramSwap(&best_combo, &tmp_histo); best_cost_diff = curr_cost_diff; best_idx1 = idx1; best_idx2 = idx2; } } if (best_idx1 >= 0) { HistogramSwap(&best_combo, &histograms[best_idx1]); // swap best_idx2 slot with last one (which is now unused) --image_histo_size; if (best_idx2 != image_histo_size) { HistogramSwap(&histograms[image_histo_size], &histograms[best_idx2]); histograms[image_histo_size] = NULL; } tries_with_no_success = 0; } if (++tries_with_no_success >= num_tries_no_success) { break; } } image_histo->size = image_histo_size; return best_combo; } // ----------------------------------------------------------------------------- // Histogram refinement // Find the best 'out' histogram for each of the 'in' histograms. // Note: we assume that out[]->bit_cost_ is already up-to-date. static void HistogramRemap(const VP8LHistogramSet* const orig_histo, const VP8LHistogramSet* const image_histo, uint16_t* const symbols) { int i; VP8LHistogram** const orig_histograms = orig_histo->histograms; VP8LHistogram** const histograms = image_histo->histograms; const int orig_histo_size = orig_histo->size; const int image_histo_size = image_histo->size; if (image_histo_size > 1) { for (i = 0; i < orig_histo_size; ++i) { int best_out = 0; double best_bits = HistogramAddThresh(histograms[0], orig_histograms[i], MAX_COST); int k; for (k = 1; k < image_histo_size; ++k) { const double cur_bits = HistogramAddThresh(histograms[k], orig_histograms[i], best_bits); if (cur_bits < best_bits) { best_bits = cur_bits; best_out = k; } } symbols[i] = best_out; } } else { assert(image_histo_size == 1); for (i = 0; i < orig_histo_size; ++i) { symbols[i] = 0; } } // Recompute each out based on raw and symbols. for (i = 0; i < image_histo_size; ++i) { HistogramClear(histograms[i]); } for (i = 0; i < orig_histo_size; ++i) { const int idx = symbols[i]; VP8LHistogramAdd(orig_histograms[i], histograms[idx], histograms[idx]); } } static double GetCombineCostFactor(int histo_size, int quality) { double combine_cost_factor = 0.16; if (quality < 90) { if (histo_size > 256) combine_cost_factor /= 2.; if (histo_size > 512) combine_cost_factor /= 2.; if (histo_size > 1024) combine_cost_factor /= 2.; if (quality <= 50) combine_cost_factor /= 2.; } return combine_cost_factor; } int VP8LGetHistoImageSymbols(int xsize, int ysize, const VP8LBackwardRefs* const refs, int quality, int low_effort, int histo_bits, int cache_bits, VP8LHistogramSet* const image_histo, VP8LHistogramSet* const tmp_histos, uint16_t* const histogram_symbols) { int ok = 0; const int histo_xsize = histo_bits ? VP8LSubSampleSize(xsize, histo_bits) : 1; const int histo_ysize = histo_bits ? VP8LSubSampleSize(ysize, histo_bits) : 1; const int image_histo_raw_size = histo_xsize * histo_ysize; const int entropy_combine_num_bins = low_effort ? NUM_PARTITIONS : BIN_SIZE; // The bin_map for every bin follows following semantics: // bin_map[n][0] = num_histo; // The number of histograms in that bin. // bin_map[n][1] = index of first histogram in that bin; // bin_map[n][num_histo] = index of last histogram in that bin; // bin_map[n][num_histo + 1] ... bin_map[n][bin_depth - 1] = unused indices. const int bin_depth = image_histo_raw_size + 1; int16_t* bin_map = NULL; VP8LHistogramSet* const orig_histo = VP8LAllocateHistogramSet(image_histo_raw_size, cache_bits); VP8LHistogram* cur_combo; const int entropy_combine = (orig_histo->size > entropy_combine_num_bins * 2) && (quality < 100); if (orig_histo == NULL) goto Error; // Don't attempt linear bin-partition heuristic for: // histograms of small sizes, as bin_map will be very sparse and; // Maximum quality (q==100), to preserve the compression gains at that level. if (entropy_combine) { const int bin_map_size = bin_depth * entropy_combine_num_bins; bin_map = (int16_t*)WebPSafeCalloc(bin_map_size, sizeof(*bin_map)); if (bin_map == NULL) goto Error; } // Construct the histograms from backward references. HistogramBuild(xsize, histo_bits, refs, orig_histo); // Copies the histograms and computes its bit_cost. HistogramCopyAndAnalyze(orig_histo, image_histo); cur_combo = tmp_histos->histograms[1]; // pick up working slot if (entropy_combine) { const double combine_cost_factor = GetCombineCostFactor(image_histo_raw_size, quality); HistogramAnalyzeEntropyBin(orig_histo, bin_map, low_effort); // Collapse histograms with similar entropy. cur_combo = HistogramCombineEntropyBin(image_histo, cur_combo, bin_map, bin_depth, entropy_combine_num_bins, combine_cost_factor, low_effort); } // Don't combine the histograms using stochastic and greedy heuristics for // low-effort compression mode. if (!low_effort || !entropy_combine) { const float x = quality / 100.f; // cubic ramp between 1 and MAX_HISTO_GREEDY: const int threshold_size = (int)(1 + (x * x * x) * (MAX_HISTO_GREEDY - 1)); cur_combo = HistogramCombineStochastic(image_histo, tmp_histos->histograms[0], cur_combo, quality, threshold_size); if ((image_histo->size <= threshold_size) && !HistogramCombineGreedy(image_histo, cur_combo)) { goto Error; } } // TODO(vikasa): Optimize HistogramRemap for low-effort compression mode also. // Find the optimal map from original histograms to the final ones. HistogramRemap(orig_histo, image_histo, histogram_symbols); ok = 1; Error: WebPSafeFree(bin_map); VP8LFreeHistogramSet(orig_histo); return ok; }