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FastMBAnalyze() for quick i16/i4 decision

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The decision is based on the variance between DC values of each
sub-4x4 block. This heuristic is rather ok for predicting whether
the 2nd transform (intra-16) is going to help or not.
The decision threshold varies with quality (=quantization).

It's only used for -m 0 and -m 1, where no full RD-opt is performed.
It actually makes these modes quite faster, with RD curve much
closer to the -m 2 mode.

Change-Id: I15f972db97ba4082cbd1dfd16bee3eb2eca701a8
This commit is contained in:
skal
2016-07-15 11:21:08 -07:00
parent 567e697776
commit 5b60db5c9d
5 changed files with 89 additions and 9 deletions
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43
src/enc/analysis.c
View File

@ -262,6 +262,29 @@ static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
return best_alpha;
}
static int FastMBAnalyze(VP8EncIterator* const it) {
// Empirical cut-off value, should be around 16 (~=block size). We use the
// [8-17] range and favor intra4 at high quality, intra16 for low quality.
const int q = (int)it->enc_->config_->quality;
const uint32_t kThreshold = 8 + (17 - 8) * q / 100;
int k;
uint32_t dc[16], m, m2;
for (k = 0; k < 16; k += 4) {
VP8Mean16x4(it->yuv_in_ + Y_OFF_ENC + k * BPS, &dc[k]);
}
for (m = 0, m2 = 0, k = 0; k < 16; ++k) {
m += dc[k];
m2 += dc[k] * dc[k];
}
if (kThreshold * m2 < m * m) {
VP8SetIntra16Mode(it, 0); // DC16
} else {
const uint8_t modes[16] = { 0 }; // DC4
VP8SetIntra4Mode(it, modes);
}
return 0;
}
static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
int best_alpha) {
uint8_t modes[16];
@ -339,13 +362,17 @@ static void MBAnalyze(VP8EncIterator* const it,
VP8SetSkip(it, 0); // not skipped
VP8SetSegment(it, 0); // default segment, spec-wise.
best_alpha = MBAnalyzeBestIntra16Mode(it);
if (enc->method_ >= 5) {
// We go and make a fast decision for intra4/intra16.
// It's usually not a good and definitive pick, but helps seeding the stats
// about level bit-cost.
// TODO(skal): improve criterion.
best_alpha = MBAnalyzeBestIntra4Mode(it, best_alpha);
if (enc->method_ <= 1) {
best_alpha = FastMBAnalyze(it);
} else {
best_alpha = MBAnalyzeBestIntra16Mode(it);
if (enc->method_ >= 5) {
// We go and make a fast decision for intra4/intra16.
// It's usually not a good and definitive pick, but helps seeding the
// stats about level bit-cost.
// TODO(skal): improve criterion.
best_alpha = MBAnalyzeBestIntra4Mode(it, best_alpha);
}
}
best_uv_alpha = MBAnalyzeBestUVMode(it);
@ -448,7 +475,7 @@ int VP8EncAnalyze(VP8Encoder* const enc) {
const int do_segments =
enc->config_->emulate_jpeg_size || // We need the complexity evaluation.
(enc->segment_hdr_.num_segments_ > 1) ||
(enc->method_ == 0); // for method 0, we need preds_[] to be filled.
(enc->method_ <= 1); // for method 0 - 1, we need preds_[] to be filled.
if (do_segments) {
const int last_row = enc->mb_h_;
// We give a little more than a half work to the main thread.

2
src/enc/webpenc.c
View File

@ -75,7 +75,7 @@ static void ResetBoundaryPredictions(VP8Encoder* const enc) {
//-------------------+---+---+---+---+---+---+---+
// dynamic proba | ~ | x | x | x | x | x | x |
//-------------------+---+---+---+---+---+---+---+
// fast mode analysis| | | | | x | x | x |
// fast mode analysis|[x]|[x]| | | x | x | x |
//-------------------+---+---+---+---+---+---+---+
// basic rd-opt | | | | x | x | x | x |
//-------------------+---+---+---+---+---+---+---+