1
// Copyright 2011 Google Inc. All Rights Reserved.
3
// Use of this source code is governed by a BSD-style license
4
// that can be found in the COPYING file in the root of the source
5
// tree. An additional intellectual property rights grant can be found
6
// in the file PATENTS. All contributing project authors may
7
// be found in the AUTHORS file in the root of the source tree.
8
// -----------------------------------------------------------------------------
10
// Macroblock analysis
12
// Author: Skal (pascal.massimino@gmail.com)
18
#include "./vp8enci.h"
20
#include "../utils/utils.h"
22
#if defined(__cplusplus) || defined(c_plusplus)
26
#define MAX_ITERS_K_MEANS 6
28
//------------------------------------------------------------------------------
29
// Smooth the segment map by replacing isolated block by the majority of its
32
static void SmoothSegmentMap(VP8Encoder* const enc) {
34
const int w = enc->mb_w_;
35
const int h = enc->mb_h_;
36
const int majority_cnt_3_x_3_grid = 5;
37
uint8_t* const tmp = (uint8_t*)WebPSafeMalloc((uint64_t)w * h, sizeof(*tmp));
38
assert((uint64_t)(w * h) == (uint64_t)w * h); // no overflow, as per spec
40
if (tmp == NULL) return;
41
for (y = 1; y < h - 1; ++y) {
42
for (x = 1; x < w - 1; ++x) {
43
int cnt[NUM_MB_SEGMENTS] = { 0 };
44
const VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
45
int majority_seg = mb->segment_;
46
// Check the 8 neighbouring segment values.
47
cnt[mb[-w - 1].segment_]++; // top-left
48
cnt[mb[-w + 0].segment_]++; // top
49
cnt[mb[-w + 1].segment_]++; // top-right
50
cnt[mb[ - 1].segment_]++; // left
51
cnt[mb[ + 1].segment_]++; // right
52
cnt[mb[ w - 1].segment_]++; // bottom-left
53
cnt[mb[ w + 0].segment_]++; // bottom
54
cnt[mb[ w + 1].segment_]++; // bottom-right
55
for (n = 0; n < NUM_MB_SEGMENTS; ++n) {
56
if (cnt[n] >= majority_cnt_3_x_3_grid) {
60
tmp[x + y * w] = majority_seg;
63
for (y = 1; y < h - 1; ++y) {
64
for (x = 1; x < w - 1; ++x) {
65
VP8MBInfo* const mb = &enc->mb_info_[x + w * y];
66
mb->segment_ = tmp[x + y * w];
72
//------------------------------------------------------------------------------
73
// set segment susceptibility alpha_ / beta_
75
static WEBP_INLINE int clip(int v, int m, int M) {
76
return (v < m) ? m : (v > M) ? M : v;
79
static void SetSegmentAlphas(VP8Encoder* const enc,
80
const int centers[NUM_MB_SEGMENTS],
82
const int nb = enc->segment_hdr_.num_segments_;
83
int min = centers[0], max = centers[0];
87
for (n = 0; n < nb; ++n) {
88
if (min > centers[n]) min = centers[n];
89
if (max < centers[n]) max = centers[n];
92
if (max == min) max = min + 1;
93
assert(mid <= max && mid >= min);
94
for (n = 0; n < nb; ++n) {
95
const int alpha = 255 * (centers[n] - mid) / (max - min);
96
const int beta = 255 * (centers[n] - min) / (max - min);
97
enc->dqm_[n].alpha_ = clip(alpha, -127, 127);
98
enc->dqm_[n].beta_ = clip(beta, 0, 255);
102
//------------------------------------------------------------------------------
103
// Compute susceptibility based on DCT-coeff histograms:
104
// the higher, the "easier" the macroblock is to compress.
106
#define MAX_ALPHA 255 // 8b of precision for susceptibilities.
107
#define ALPHA_SCALE (2 * MAX_ALPHA) // scaling factor for alpha.
108
#define DEFAULT_ALPHA (-1)
109
#define IS_BETTER_ALPHA(alpha, best_alpha) ((alpha) > (best_alpha))
111
static int FinalAlphaValue(int alpha) {
112
alpha = MAX_ALPHA - alpha;
113
return clip(alpha, 0, MAX_ALPHA);
116
static int GetAlpha(const VP8Histogram* const histo) {
117
int max_value = 0, last_non_zero = 1;
120
for (k = 0; k <= MAX_COEFF_THRESH; ++k) {
121
const int value = histo->distribution[k];
123
if (value > max_value) max_value = value;
127
// 'alpha' will later be clipped to [0..MAX_ALPHA] range, clamping outer
128
// values which happen to be mostly noise. This leaves the maximum precision
129
// for handling the useful small values which contribute most.
130
alpha = (max_value > 1) ? ALPHA_SCALE * last_non_zero / max_value : 0;
134
static void MergeHistograms(const VP8Histogram* const in,
135
VP8Histogram* const out) {
137
for (i = 0; i <= MAX_COEFF_THRESH; ++i) {
138
out->distribution[i] += in->distribution[i];
142
//------------------------------------------------------------------------------
143
// Simplified k-Means, to assign Nb segments based on alpha-histogram
145
static void AssignSegments(VP8Encoder* const enc,
146
const int alphas[MAX_ALPHA + 1]) {
147
const int nb = enc->segment_hdr_.num_segments_;
148
int centers[NUM_MB_SEGMENTS];
149
int weighted_average = 0;
150
int map[MAX_ALPHA + 1];
152
int min_a = 0, max_a = MAX_ALPHA, range_a;
153
// 'int' type is ok for histo, and won't overflow
154
int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
157
for (n = 0; n <= MAX_ALPHA && alphas[n] == 0; ++n) {}
159
for (n = MAX_ALPHA; n > min_a && alphas[n] == 0; --n) {}
161
range_a = max_a - min_a;
163
// Spread initial centers evenly
164
for (n = 1, k = 0; n < 2 * nb; n += 2) {
165
centers[k++] = min_a + (n * range_a) / (2 * nb);
168
for (k = 0; k < MAX_ITERS_K_MEANS; ++k) { // few iters are enough
172
for (n = 0; n < nb; ++n) {
176
// Assign nearest center for each 'a'
177
n = 0; // track the nearest center for current 'a'
178
for (a = min_a; a <= max_a; ++a) {
180
while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
184
// accumulate contribution into best centroid
185
dist_accum[n] += a * alphas[a];
186
accum[n] += alphas[a];
189
// All point are classified. Move the centroids to the
190
// center of their respective cloud.
192
weighted_average = 0;
194
for (n = 0; n < nb; ++n) {
196
const int new_center = (dist_accum[n] + accum[n] / 2) / accum[n];
197
displaced += abs(centers[n] - new_center);
198
centers[n] = new_center;
199
weighted_average += new_center * accum[n];
200
total_weight += accum[n];
203
weighted_average = (weighted_average + total_weight / 2) / total_weight;
204
if (displaced < 5) break; // no need to keep on looping...
207
// Map each original value to the closest centroid
208
for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
209
VP8MBInfo* const mb = &enc->mb_info_[n];
210
const int alpha = mb->alpha_;
211
mb->segment_ = map[alpha];
212
mb->alpha_ = centers[map[alpha]]; // for the record.
216
const int smooth = (enc->config_->preprocessing & 1);
217
if (smooth) SmoothSegmentMap(enc);
220
SetSegmentAlphas(enc, centers, weighted_average); // pick some alphas.
223
//------------------------------------------------------------------------------
224
// Macroblock analysis: collect histogram for each mode, deduce the maximal
225
// susceptibility and set best modes for this macroblock.
226
// Segment assignment is done later.
228
// Number of modes to inspect for alpha_ evaluation. For high-quality settings
229
// (method >= FAST_ANALYSIS_METHOD) we don't need to test all the possible modes
230
// during the analysis phase.
231
#define FAST_ANALYSIS_METHOD 4 // method above which we do partial analysis
232
#define MAX_INTRA16_MODE 2
233
#define MAX_INTRA4_MODE 2
234
#define MAX_UV_MODE 2
236
static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
238
(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA16_MODE
241
int best_alpha = DEFAULT_ALPHA;
244
VP8MakeLuma16Preds(it);
245
for (mode = 0; mode < max_mode; ++mode) {
246
VP8Histogram histo = { { 0 } };
249
VP8CollectHistogram(it->yuv_in_ + Y_OFF,
250
it->yuv_p_ + VP8I16ModeOffsets[mode],
252
alpha = GetAlpha(&histo);
253
if (IS_BETTER_ALPHA(alpha, best_alpha)) {
258
VP8SetIntra16Mode(it, best_mode);
262
static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
266
(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_INTRA4_MODE
269
VP8Histogram total_histo = { { 0 } };
272
VP8IteratorStartI4(it);
275
int best_mode_alpha = DEFAULT_ALPHA;
276
VP8Histogram histos[2];
277
const uint8_t* const src = it->yuv_in_ + Y_OFF + VP8Scan[it->i4_];
279
VP8MakeIntra4Preds(it);
280
for (mode = 0; mode < max_mode; ++mode) {
283
memset(&histos[cur_histo], 0, sizeof(histos[cur_histo]));
284
VP8CollectHistogram(src, it->yuv_p_ + VP8I4ModeOffsets[mode],
285
0, 1, &histos[cur_histo]);
286
alpha = GetAlpha(&histos[cur_histo]);
287
if (IS_BETTER_ALPHA(alpha, best_mode_alpha)) {
288
best_mode_alpha = alpha;
289
modes[it->i4_] = mode;
290
cur_histo ^= 1; // keep track of best histo so far.
293
// accumulate best histogram
294
MergeHistograms(&histos[cur_histo ^ 1], &total_histo);
295
// Note: we reuse the original samples for predictors
296
} while (VP8IteratorRotateI4(it, it->yuv_in_ + Y_OFF));
298
i4_alpha = GetAlpha(&total_histo);
299
if (IS_BETTER_ALPHA(i4_alpha, best_alpha)) {
300
VP8SetIntra4Mode(it, modes);
301
best_alpha = i4_alpha;
306
static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
307
int best_alpha = DEFAULT_ALPHA;
310
(it->enc_->method_ >= FAST_ANALYSIS_METHOD) ? MAX_UV_MODE
313
VP8MakeChroma8Preds(it);
314
for (mode = 0; mode < max_mode; ++mode) {
315
VP8Histogram histo = { { 0 } };
317
VP8CollectHistogram(it->yuv_in_ + U_OFF,
318
it->yuv_p_ + VP8UVModeOffsets[mode],
319
16, 16 + 4 + 4, &histo);
320
alpha = GetAlpha(&histo);
321
if (IS_BETTER_ALPHA(alpha, best_alpha)) {
326
VP8SetIntraUVMode(it, best_mode);
330
static void MBAnalyze(VP8EncIterator* const it,
331
int alphas[MAX_ALPHA + 1],
332
int* const alpha, int* const uv_alpha) {
333
const VP8Encoder* const enc = it->enc_;
334
int best_alpha, best_uv_alpha;
336
VP8SetIntra16Mode(it, 0); // default: Intra16, DC_PRED
337
VP8SetSkip(it, 0); // not skipped
338
VP8SetSegment(it, 0); // default segment, spec-wise.
340
best_alpha = MBAnalyzeBestIntra16Mode(it);
341
if (enc->method_ >= 5) {
342
// We go and make a fast decision for intra4/intra16.
343
// It's usually not a good and definitive pick, but helps seeding the stats
344
// about level bit-cost.
345
// TODO(skal): improve criterion.
346
best_alpha = MBAnalyzeBestIntra4Mode(it, best_alpha);
348
best_uv_alpha = MBAnalyzeBestUVMode(it);
350
// Final susceptibility mix
351
best_alpha = (3 * best_alpha + best_uv_alpha + 2) >> 2;
352
best_alpha = FinalAlphaValue(best_alpha);
353
alphas[best_alpha]++;
354
it->mb_->alpha_ = best_alpha; // for later remapping.
356
// Accumulate for later complexity analysis.
357
*alpha += best_alpha; // mixed susceptibility (not just luma)
358
*uv_alpha += best_uv_alpha;
361
static void DefaultMBInfo(VP8MBInfo* const mb) {
362
mb->type_ = 1; // I16x16
364
mb->skip_ = 0; // not skipped
365
mb->segment_ = 0; // default segment
369
//------------------------------------------------------------------------------
370
// Main analysis loop:
371
// Collect all susceptibilities for each macroblock and record their
372
// distribution in alphas[]. Segments is assigned a-posteriori, based on
374
// We also pick an intra16 prediction mode, which shouldn't be considered
375
// final except for fast-encode settings. We can also pick some intra4 modes
376
// and decide intra4/intra16, but that's usually almost always a bad choice at
379
static void ResetAllMBInfo(VP8Encoder* const enc) {
381
for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
382
DefaultMBInfo(&enc->mb_info_[n]);
384
// Default susceptibilities.
385
enc->dqm_[0].alpha_ = 0;
386
enc->dqm_[0].beta_ = 0;
387
// Note: we can't compute this alpha_ / uv_alpha_.
388
WebPReportProgress(enc->pic_, enc->percent_ + 20, &enc->percent_);
391
int VP8EncAnalyze(VP8Encoder* const enc) {
393
const int do_segments =
394
enc->config_->emulate_jpeg_size || // We need the complexity evaluation.
395
(enc->segment_hdr_.num_segments_ > 1) ||
396
(enc->method_ == 0); // for method 0, we need preds_[] to be filled.
400
int alphas[MAX_ALPHA + 1] = { 0 };
403
VP8IteratorInit(enc, &it);
405
VP8IteratorImport(&it);
406
MBAnalyze(&it, alphas, &enc->alpha_, &enc->uv_alpha_);
407
ok = VP8IteratorProgress(&it, 20);
408
// Let's pretend we have perfect lossless reconstruction.
409
} while (ok && VP8IteratorNext(&it, it.yuv_in_));
410
enc->alpha_ /= enc->mb_w_ * enc->mb_h_;
411
enc->uv_alpha_ /= enc->mb_w_ * enc->mb_h_;
412
if (ok) AssignSegments(enc, alphas);
413
} else { // Use only one default segment.
419
#if defined(__cplusplus) || defined(c_plusplus)