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webp-src/src/enc/analysis.c  view on Meta::CPAN

// 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/
// -----------------------------------------------------------------------------
//
// Macroblock analysis
//
// Author: Skal (pascal.massimino@gmail.com)

#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include "./vp8enci.h"
#include "./cost.h"
#include "../utils/utils.h"

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

#define MAX_ITERS_K_MEANS  6

//------------------------------------------------------------------------------
// Smooth the segment map by replacing isolated block by the majority of its
// neighbours.

static void SmoothSegmentMap(VP8Encoder* const enc) {
  int n, x, y;
  const int w = enc->mb_w_;
  const int h = enc->mb_h_;
  const int majority_cnt_3_x_3_grid = 5;
  uint8_t* const tmp = (uint8_t*)WebPSafeMalloc((uint64_t)w * h, sizeof(*tmp));
  assert((uint64_t)(w * h) == (uint64_t)w * h);   // no overflow, as per spec

  if (tmp == NULL) return;
  for (y = 1; y < h - 1; ++y) {
    for (x = 1; x < w - 1; ++x) {
      int cnt[NUM_MB_SEGMENTS] = { 0 };
      const VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
      int majority_seg = mb->segment_;
      // Check the 8 neighbouring segment values.
      cnt[mb[-w - 1].segment_]++;  // top-left
      cnt[mb[-w + 0].segment_]++;  // top
      cnt[mb[-w + 1].segment_]++;  // top-right
      cnt[mb[   - 1].segment_]++;  // left
      cnt[mb[   + 1].segment_]++;  // right
      cnt[mb[ w - 1].segment_]++;  // bottom-left
      cnt[mb[ w + 0].segment_]++;  // bottom
      cnt[mb[ w + 1].segment_]++;  // bottom-right
      for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
        if (cnt[n] >= majority_cnt_3_x_3_grid) {
          majority_seg = n;
        }
      }
      tmp[x + y * w] = majority_seg;
    }
  }
  for (y = 1; y < h - 1; ++y) {
    for (x = 1; x < w - 1; ++x) {
      VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
      mb->segment_ = tmp[x + y * w];
    }
  }
  free(tmp);
}

webp-src/src/enc/analysis.c  view on Meta::CPAN

  for (n = 1, k = 0; n < 2 * nb; n += 2) {
    centers[k++] = min_a + (n * range_a) / (2 * nb);
  }

  for (k = 0; k < MAX_ITERS_K_MEANS; ++k) {     // few iters are enough
    int total_weight;
    int displaced;
    // Reset stats
    for (n = 0; n < nb; ++n) {
      accum[n] = 0;
      dist_accum[n] = 0;
    }
    // Assign nearest center for each 'a'
    n = 0;    // track the nearest center for current 'a'
    for (a = min_a; a <= max_a; ++a) {
      if (alphas[a]) {
        while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
          n++;
        }
        map[a] = n;
        // accumulate contribution into best centroid
        dist_accum[n] += a * alphas[a];
        accum[n] += alphas[a];
      }
    }
    // All point are classified. Move the centroids to the
    // center of their respective cloud.
    displaced = 0;
    weighted_average = 0;
    total_weight = 0;
    for (n = 0; n < nb; ++n) {
      if (accum[n]) {
        const int new_center = (dist_accum[n] + accum[n] / 2) / accum[n];
        displaced += abs(centers[n] - new_center);
        centers[n] = new_center;
        weighted_average += new_center * accum[n];
        total_weight += accum[n];
      }
    }
    weighted_average = (weighted_average + total_weight / 2) / total_weight;
    if (displaced < 5) break;   // no need to keep on looping...
  }

  // Map each original value to the closest centroid
  for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
    VP8MBInfo* const mb = &enc->mb_info_[n];
    const int alpha = mb->alpha_;
    mb->segment_ = map[alpha];
    mb->alpha_ = centers[map[alpha]];  // for the record.
  }

  if (nb > 1) {
    const int smooth = (enc->config_->preprocessing & 1);
    if (smooth) SmoothSegmentMap(enc);
  }

  SetSegmentAlphas(enc, centers, weighted_average);  // pick some alphas.
}

//------------------------------------------------------------------------------
// Macroblock analysis: collect histogram for each mode, deduce the maximal
// susceptibility and set best modes for this macroblock.
// Segment assignment is done later.

// Number of modes to inspect for alpha_ evaluation. For high-quality settings
// (method >= FAST_ANALYSIS_METHOD) we don't need to test all the possible modes
// during the analysis phase.
#define FAST_ANALYSIS_METHOD 4  // method above which we do partial analysis
#define MAX_INTRA16_MODE 2
#define MAX_INTRA4_MODE  2
#define MAX_UV_MODE      2

static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
  const int max_mode =
      (it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA16_MODE
                                                  : NUM_PRED_MODES;
  int mode;
  int best_alpha = DEFAULT_ALPHA;
  int best_mode = 0;

  VP8MakeLuma16Preds(it);
  for (mode = 0; mode < max_mode; ++mode) {
    VP8Histogram histo = { { 0 } };
    int alpha;

    VP8CollectHistogram(it->yuv_in_ + Y_OFF,
                        it->yuv_p_ + VP8I16ModeOffsets[mode],
                        0, 16, &histo);
    alpha = GetAlpha(&histo);
    if (IS_BETTER_ALPHA(alpha, best_alpha)) {
      best_alpha = alpha;
      best_mode = mode;
    }
  }
  VP8SetIntra16Mode(it, best_mode);
  return best_alpha;
}

static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
                                   int best_alpha) {
  uint8_t modes[16];
  const int max_mode =
      (it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA4_MODE
                                                  : NUM_BMODES;
  int i4_alpha;
  VP8Histogram total_histo = { { 0 } };
  int cur_histo = 0;

  VP8IteratorStartI4(it);
  do {
    int mode;
    int best_mode_alpha = DEFAULT_ALPHA;
    VP8Histogram histos[2];
    const uint8_t* const src = it->yuv_in_ + Y_OFF + VP8Scan[it->i4_];

    VP8MakeIntra4Preds(it);
    for (mode = 0; mode < max_mode; ++mode) {
      int alpha;

      memset(&histos[cur_histo], 0, sizeof(histos[cur_histo]));
      VP8CollectHistogram(src, it->yuv_p_ + VP8I4ModeOffsets[mode],