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detect flatness in blocks and favor DC prediction

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this avoids local-minima that look bad, even if the distortion
looks low (e.g. gradients, sky,...). Mostly visible in the q=50-80 range.
Output size is mostly unchanged.

Change-Id: I425b600ec45420db409911367cda375870bc2c63
This commit is contained in:
skal 2013-11-01 00:47:04 +01:00
parent ebc9b1eedf
commit e3312ea681
1 changed files with 37 additions and 3 deletions
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40
src/enc/quant.c
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@ -32,6 +32,13 @@
#define I4_PENALTY 4000 // Rate-penalty for quick i4/i16 decision
// number of non-zero coeffs below which we consider the block very flat
// (and apply a penalty to complex predictions)
#define FLATNESS_LIMIT_I16 10 // I16 mode
#define FLATNESS_LIMIT_I4 3 // I4 mode
#define FLATNESS_LIMIT_UV 2 // UV mode
#define FLATNESS_PENALTY 140 // roughly ~1bit per block
#define MULT_8B(a, b) (((a) * (b) + 128) >> 8)
// #define DEBUG_BLOCK
@ -830,7 +837,21 @@ static void SwapOut(VP8EncIterator* const it) {
SwapPtr(&it->yuv_out_, &it->yuv_out2_);
}
static score_t IsFlat(const int16_t* levels, int num_blocks, score_t thresh) {
score_t score = 0;
while (num_blocks-- > 0) { // TODO(skal): refine positional scoring?
int i;
for (i = 1; i < 16; ++i) { // omit DC, we're only interested in AC
score += (levels[i] != 0);
if (score > thresh) return 0;
}
levels += 16;
}
return 1;
}
static void PickBestIntra16(VP8EncIterator* const it, VP8ModeScore* const rd) {
const int kNumBlocks = 16;
VP8Encoder* const enc = it->enc_;
VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
const int lambda = dqm->lambda_i16_;
@ -851,8 +872,13 @@ static void PickBestIntra16(VP8EncIterator* const it, VP8ModeScore* const rd) {
rd16.D = VP8SSE16x16(src, tmp_dst);
rd16.SD = tlambda ? MULT_8B(tlambda, VP8TDisto16x16(src, tmp_dst, kWeightY))
: 0;
rd16.R = VP8GetCostLuma16(it, &rd16);
rd16.H = VP8FixedCostsI16[mode];
rd16.R = VP8GetCostLuma16(it, &rd16);
if (mode > 0 &&
IsFlat(rd16.y_ac_levels[0], kNumBlocks, FLATNESS_LIMIT_I16)) {
// penalty to avoid flat area to be mispredicted by complex mode
rd16.R += FLATNESS_PENALTY * kNumBlocks;
}
// Since we always examine Intra16 first, we can overwrite *rd directly.
SetRDScore(lambda, &rd16);
@ -907,6 +933,7 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
SetRDScore(dqm->lambda_mode_, &rd_best);
VP8IteratorStartI4(it);
do {
const int kNumBlocks = 1;
VP8ModeScore rd_i4;
int mode;
int best_mode = -1;
@ -930,8 +957,11 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
rd_tmp.SD =
tlambda ? MULT_8B(tlambda, VP8TDisto4x4(src, tmp_dst, kWeightY))
: 0;
rd_tmp.R = VP8GetCostLuma4(it, tmp_levels);
rd_tmp.H = mode_costs[mode];
rd_tmp.R = VP8GetCostLuma4(it, tmp_levels);
if (mode > 0 && IsFlat(tmp_levels, kNumBlocks, FLATNESS_LIMIT_I4)) {
rd_tmp.R += FLATNESS_PENALTY * kNumBlocks;
}
SetRDScore(lambda, &rd_tmp);
if (best_mode < 0 || rd_tmp.score < rd_i4.score) {
@ -969,6 +999,7 @@ static int PickBestIntra4(VP8EncIterator* const it, VP8ModeScore* const rd) {
//------------------------------------------------------------------------------
static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) {
const int kNumBlocks = 8;
const VP8Encoder* const enc = it->enc_;
const VP8SegmentInfo* const dqm = &enc->dqm_[it->mb_->segment_];
const int lambda = dqm->lambda_uv_;
@ -989,8 +1020,11 @@ static void PickBestUV(VP8EncIterator* const it, VP8ModeScore* const rd) {
// Compute RD-score
rd_uv.D = VP8SSE16x8(src, tmp_dst);
rd_uv.SD = 0; // TODO: should we call TDisto? it tends to flatten areas.
rd_uv.R = VP8GetCostUV(it, &rd_uv);
rd_uv.H = VP8FixedCostsUV[mode];
rd_uv.R = VP8GetCostUV(it, &rd_uv);
if (mode > 0 && IsFlat(rd_uv.uv_levels[0], kNumBlocks, FLATNESS_LIMIT_UV)) {
rd_uv.R += FLATNESS_PENALTY * kNumBlocks;
}
SetRDScore(lambda, &rd_uv);
if (mode == 0 || rd_uv.score < rd_best.score) {