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422 lines
14 KiB
C
422 lines
14 KiB
C
// Copyright 2011 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Macroblock analysis
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//
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// Author: Skal (pascal.massimino@gmail.com)
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "./vp8enci.h"
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#include "./cost.h"
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#include "../utils/utils.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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#define MAX_ITERS_K_MEANS 6
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//------------------------------------------------------------------------------
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// Smooth the segment map by replacing isolated block by the majority of its
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// neighbours.
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static void SmoothSegmentMap(VP8Encoder* const enc) {
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int n, x, y;
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const int w = enc->mb_w_;
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const int h = enc->mb_h_;
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const int majority_cnt_3_x_3_grid = 5;
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uint8_t* const tmp = (uint8_t*)WebPSafeMalloc((uint64_t)w * h, sizeof(*tmp));
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assert((uint64_t)(w * h) == (uint64_t)w * h); // no overflow, as per spec
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if (tmp == NULL) return;
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for (y = 1; y < h - 1; ++y) {
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for (x = 1; x < w - 1; ++x) {
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int cnt[NUM_MB_SEGMENTS] = { 0 };
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const VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
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int majority_seg = mb->segment_;
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// Check the 8 neighbouring segment values.
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cnt[mb[-w - 1].segment_]++; // top-left
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cnt[mb[-w + 0].segment_]++; // top
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cnt[mb[-w + 1].segment_]++; // top-right
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cnt[mb[ - 1].segment_]++; // left
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cnt[mb[ + 1].segment_]++; // right
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cnt[mb[ w - 1].segment_]++; // bottom-left
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cnt[mb[ w + 0].segment_]++; // bottom
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cnt[mb[ w + 1].segment_]++; // bottom-right
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for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
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if (cnt[n] >= majority_cnt_3_x_3_grid) {
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majority_seg = n;
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}
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}
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tmp[x + y * w] = majority_seg;
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}
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}
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for (y = 1; y < h - 1; ++y) {
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for (x = 1; x < w - 1; ++x) {
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VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
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mb->segment_ = tmp[x + y * w];
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}
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}
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free(tmp);
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}
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//------------------------------------------------------------------------------
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// set segment susceptibility alpha_ / beta_
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static WEBP_INLINE int clip(int v, int m, int M) {
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return (v < m) ? m : (v > M) ? M : v;
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}
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static void SetSegmentAlphas(VP8Encoder* const enc,
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const int centers[NUM_MB_SEGMENTS],
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int mid) {
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const int nb = enc->segment_hdr_.num_segments_;
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int min = centers[0], max = centers[0];
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int n;
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if (nb > 1) {
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for (n = 0; n < nb; ++n) {
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if (min > centers[n]) min = centers[n];
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if (max < centers[n]) max = centers[n];
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}
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}
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if (max == min) max = min + 1;
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assert(mid <= max && mid >= min);
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for (n = 0; n < nb; ++n) {
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const int alpha = 255 * (centers[n] - mid) / (max - min);
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const int beta = 255 * (centers[n] - min) / (max - min);
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enc->dqm_[n].alpha_ = clip(alpha, -127, 127);
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enc->dqm_[n].beta_ = clip(beta, 0, 255);
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}
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}
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//------------------------------------------------------------------------------
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// Compute susceptibility based on DCT-coeff histograms:
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// the higher, the "easier" the macroblock is to compress.
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#define MAX_ALPHA 255 // 8b of precision for susceptibilities.
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#define ALPHA_SCALE (2 * MAX_ALPHA) // scaling factor for alpha.
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#define DEFAULT_ALPHA (-1)
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#define IS_BETTER_ALPHA(alpha, best_alpha) ((alpha) > (best_alpha))
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static int FinalAlphaValue(int alpha) {
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alpha = MAX_ALPHA - alpha;
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return clip(alpha, 0, MAX_ALPHA);
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}
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static int GetAlpha(const VP8Histogram* const histo) {
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int max_value = 0, last_non_zero = 1;
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int k;
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int alpha;
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for (k = 0; k <= MAX_COEFF_THRESH; ++k) {
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const int value = histo->distribution[k];
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if (value > 0) {
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if (value > max_value) max_value = value;
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last_non_zero = k;
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}
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}
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// 'alpha' will later be clipped to [0..MAX_ALPHA] range, clamping outer
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// values which happen to be mostly noise. This leaves the maximum precision
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// for handling the useful small values which contribute most.
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alpha = (max_value > 1) ? ALPHA_SCALE * last_non_zero / max_value : 0;
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return alpha;
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}
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static void MergeHistograms(const VP8Histogram* const in,
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VP8Histogram* const out) {
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int i;
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for (i = 0; i <= MAX_COEFF_THRESH; ++i) {
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out->distribution[i] += in->distribution[i];
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}
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}
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//------------------------------------------------------------------------------
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// Simplified k-Means, to assign Nb segments based on alpha-histogram
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static void AssignSegments(VP8Encoder* const enc,
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const int alphas[MAX_ALPHA + 1]) {
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const int nb = enc->segment_hdr_.num_segments_;
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int centers[NUM_MB_SEGMENTS];
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int weighted_average = 0;
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int map[MAX_ALPHA + 1];
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int a, n, k;
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int min_a = 0, max_a = MAX_ALPHA, range_a;
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// 'int' type is ok for histo, and won't overflow
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int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
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// bracket the input
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for (n = 0; n <= MAX_ALPHA && alphas[n] == 0; ++n) {}
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min_a = n;
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for (n = MAX_ALPHA; n > min_a && alphas[n] == 0; --n) {}
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max_a = n;
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range_a = max_a - min_a;
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// Spread initial centers evenly
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for (n = 1, k = 0; n < 2 * nb; n += 2) {
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centers[k++] = min_a + (n * range_a) / (2 * nb);
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}
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for (k = 0; k < MAX_ITERS_K_MEANS; ++k) { // few iters are enough
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int total_weight;
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int displaced;
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// Reset stats
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for (n = 0; n < nb; ++n) {
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accum[n] = 0;
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dist_accum[n] = 0;
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}
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// Assign nearest center for each 'a'
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n = 0; // track the nearest center for current 'a'
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for (a = min_a; a <= max_a; ++a) {
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if (alphas[a]) {
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while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
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n++;
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}
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map[a] = n;
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// accumulate contribution into best centroid
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dist_accum[n] += a * alphas[a];
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accum[n] += alphas[a];
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}
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}
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// All point are classified. Move the centroids to the
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// center of their respective cloud.
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displaced = 0;
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weighted_average = 0;
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total_weight = 0;
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for (n = 0; n < nb; ++n) {
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if (accum[n]) {
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const int new_center = (dist_accum[n] + accum[n] / 2) / accum[n];
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displaced += abs(centers[n] - new_center);
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centers[n] = new_center;
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weighted_average += new_center * accum[n];
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total_weight += accum[n];
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}
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}
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weighted_average = (weighted_average + total_weight / 2) / total_weight;
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if (displaced < 5) break; // no need to keep on looping...
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}
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// Map each original value to the closest centroid
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for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
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VP8MBInfo* const mb = &enc->mb_info_[n];
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const int alpha = mb->alpha_;
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mb->segment_ = map[alpha];
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mb->alpha_ = centers[map[alpha]]; // for the record.
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}
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if (nb > 1) {
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const int smooth = (enc->config_->preprocessing & 1);
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if (smooth) SmoothSegmentMap(enc);
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}
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SetSegmentAlphas(enc, centers, weighted_average); // pick some alphas.
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}
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//------------------------------------------------------------------------------
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// Macroblock analysis: collect histogram for each mode, deduce the maximal
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// susceptibility and set best modes for this macroblock.
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// Segment assignment is done later.
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// Number of modes to inspect for alpha_ evaluation. For high-quality settings
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// (method >= FAST_ANALYSIS_METHOD) we don't need to test all the possible modes
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// during the analysis phase.
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#define FAST_ANALYSIS_METHOD 4 // method above which we do partial analysis
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#define MAX_INTRA16_MODE 2
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#define MAX_INTRA4_MODE 2
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#define MAX_UV_MODE 2
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static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
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const int max_mode =
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(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA16_MODE
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: NUM_PRED_MODES;
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int mode;
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int best_alpha = DEFAULT_ALPHA;
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int best_mode = 0;
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VP8MakeLuma16Preds(it);
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for (mode = 0; mode < max_mode; ++mode) {
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VP8Histogram histo = { { 0 } };
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int alpha;
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VP8CollectHistogram(it->yuv_in_ + Y_OFF,
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it->yuv_p_ + VP8I16ModeOffsets[mode],
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0, 16, &histo);
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alpha = GetAlpha(&histo);
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if (IS_BETTER_ALPHA(alpha, best_alpha)) {
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best_alpha = alpha;
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best_mode = mode;
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}
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}
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VP8SetIntra16Mode(it, best_mode);
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return best_alpha;
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}
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static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
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int best_alpha) {
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uint8_t modes[16];
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const int max_mode =
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(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA4_MODE
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: NUM_BMODES;
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int i4_alpha;
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VP8Histogram total_histo = { { 0 } };
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int cur_histo = 0;
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VP8IteratorStartI4(it);
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do {
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int mode;
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int best_mode_alpha = DEFAULT_ALPHA;
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VP8Histogram histos[2];
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const uint8_t* const src = it->yuv_in_ + Y_OFF + VP8Scan[it->i4_];
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VP8MakeIntra4Preds(it);
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for (mode = 0; mode < max_mode; ++mode) {
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int alpha;
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memset(&histos[cur_histo], 0, sizeof(histos[cur_histo]));
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VP8CollectHistogram(src, it->yuv_p_ + VP8I4ModeOffsets[mode],
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0, 1, &histos[cur_histo]);
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alpha = GetAlpha(&histos[cur_histo]);
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if (IS_BETTER_ALPHA(alpha, best_mode_alpha)) {
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best_mode_alpha = alpha;
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modes[it->i4_] = mode;
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cur_histo ^= 1; // keep track of best histo so far.
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}
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}
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// accumulate best histogram
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MergeHistograms(&histos[cur_histo ^ 1], &total_histo);
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// Note: we reuse the original samples for predictors
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} while (VP8IteratorRotateI4(it, it->yuv_in_ + Y_OFF));
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i4_alpha = GetAlpha(&total_histo);
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if (IS_BETTER_ALPHA(i4_alpha, best_alpha)) {
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VP8SetIntra4Mode(it, modes);
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best_alpha = i4_alpha;
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}
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return best_alpha;
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}
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static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
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int best_alpha = DEFAULT_ALPHA;
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int best_mode = 0;
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const int max_mode =
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(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_UV_MODE
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: NUM_PRED_MODES;
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int mode;
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VP8MakeChroma8Preds(it);
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for (mode = 0; mode < max_mode; ++mode) {
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VP8Histogram histo = { { 0 } };
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int alpha;
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VP8CollectHistogram(it->yuv_in_ + U_OFF,
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it->yuv_p_ + VP8UVModeOffsets[mode],
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16, 16 + 4 + 4, &histo);
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alpha = GetAlpha(&histo);
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if (IS_BETTER_ALPHA(alpha, best_alpha)) {
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best_alpha = alpha;
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best_mode = mode;
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}
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}
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VP8SetIntraUVMode(it, best_mode);
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return best_alpha;
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}
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static void MBAnalyze(VP8EncIterator* const it,
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int alphas[MAX_ALPHA + 1],
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int* const alpha, int* const uv_alpha) {
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const VP8Encoder* const enc = it->enc_;
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int best_alpha, best_uv_alpha;
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VP8SetIntra16Mode(it, 0); // default: Intra16, DC_PRED
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VP8SetSkip(it, 0); // not skipped
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VP8SetSegment(it, 0); // default segment, spec-wise.
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best_alpha = MBAnalyzeBestIntra16Mode(it);
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if (enc->method_ >= 5) {
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// We go and make a fast decision for intra4/intra16.
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// It's usually not a good and definitive pick, but helps seeding the stats
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// about level bit-cost.
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// TODO(skal): improve criterion.
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best_alpha = MBAnalyzeBestIntra4Mode(it, best_alpha);
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}
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best_uv_alpha = MBAnalyzeBestUVMode(it);
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// Final susceptibility mix
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best_alpha = (3 * best_alpha + best_uv_alpha + 2) >> 2;
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best_alpha = FinalAlphaValue(best_alpha);
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alphas[best_alpha]++;
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it->mb_->alpha_ = best_alpha; // for later remapping.
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// Accumulate for later complexity analysis.
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*alpha += best_alpha; // mixed susceptibility (not just luma)
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*uv_alpha += best_uv_alpha;
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}
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static void DefaultMBInfo(VP8MBInfo* const mb) {
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mb->type_ = 1; // I16x16
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mb->uv_mode_ = 0;
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mb->skip_ = 0; // not skipped
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mb->segment_ = 0; // default segment
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mb->alpha_ = 0;
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}
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//------------------------------------------------------------------------------
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// Main analysis loop:
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// Collect all susceptibilities for each macroblock and record their
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// distribution in alphas[]. Segments is assigned a-posteriori, based on
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// this histogram.
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// We also pick an intra16 prediction mode, which shouldn't be considered
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// final except for fast-encode settings. We can also pick some intra4 modes
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// and decide intra4/intra16, but that's usually almost always a bad choice at
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// this stage.
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static void ResetAllMBInfo(VP8Encoder* const enc) {
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int n;
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for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
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DefaultMBInfo(&enc->mb_info_[n]);
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}
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// Default susceptibilities.
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enc->dqm_[0].alpha_ = 0;
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enc->dqm_[0].beta_ = 0;
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// Note: we can't compute this alpha_ / uv_alpha_.
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WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
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}
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int VP8EncAnalyze(VP8Encoder* const enc) {
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int ok = 1;
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const int do_segments =
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enc->config_->emulate_jpeg_size || // We need the complexity evaluation.
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(enc->segment_hdr_.num_segments_ > 1) ||
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(enc->method_ == 0); // for method 0, we need preds_[] to be filled.
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enc->alpha_ = 0;
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enc->uv_alpha_ = 0;
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if (do_segments) {
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int alphas[MAX_ALPHA + 1] = { 0 };
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VP8EncIterator it;
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VP8IteratorInit(enc, &it);
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do {
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VP8IteratorImport(&it);
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MBAnalyze(&it, alphas, &enc->alpha_, &enc->uv_alpha_);
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ok = VP8IteratorProgress(&it, 20);
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// Let's pretend we have perfect lossless reconstruction.
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} while (ok && VP8IteratorNext(&it, it.yuv_in_));
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enc->alpha_ /= enc->mb_w_ * enc->mb_h_;
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enc->uv_alpha_ /= enc->mb_w_ * enc->mb_h_;
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if (ok) AssignSegments(enc, alphas);
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} else { // Use only one default segment.
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ResetAllMBInfo(enc);
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}
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return ok;
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} // extern "C"
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#endif
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