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)