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enable dc error-diffusion always

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for q<=98, we always enable error diffusion.

+ reduce storage 2x by using int8_t
+ make the error diffusion more robust

BUG=webp:340,308

Change-Id: I0608df839ff7b64d6843005a0f81d2577143af9e
This commit is contained in:
Pascal Massimino 2017-12-22 08:01:48 -08:00
parent c2d04f3eb2
commit 815652de03
2 changed files with 29 additions and 24 deletions
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47
src/enc/quant_enc.c
View File

@ -829,11 +829,12 @@ static int ReconstructIntra4(VP8EncIterator* const it,
//------------------------------------------------------------------------------
// DC-error diffusion
// Diffusion weights. We under-correct a bit (3/4th of the error is actually
// Diffusion weights. We under-correct a bit (15/16th of the error is actually
// diffused) to avoid 'rainbow' chessboard pattern of blocks at q~=0.
#define C1 2 // fraction of error sent to the 4x4 block below
#define C2 1 // fraction of error sent to the 4x4 block on the right
#define DSHIFT 2
#define C1 7 // fraction of error sent to the 4x4 block below
#define C2 8 // fraction of error sent to the 4x4 block on the right
#define DSHIFT 4
#define DSCALE 1 // storage descaling, needed to make the error fit int8_t
// Quantize as usual, but also compute and return the quantization error.
// Error is already divided by DSHIFT.
@ -845,10 +846,10 @@ static int QuantizeSingle(int16_t* const v, const VP8Matrix* const mtx) {
const int qV = QUANTDIV(V, mtx->iq_[0], mtx->bias_[0]) * mtx->q_[0];
const int err = (V - qV);
*v = sign ? -qV : qV;
return (sign ? -err : err) >> DSHIFT;
return (sign ? -err : err) >> DSCALE;
}
*v = 0;
return (sign ? -V : V) >> DSHIFT;
return (sign ? -V : V) >> DSCALE;
}
static void CorrectDCValues(const VP8EncIterator* const it,
@ -863,21 +864,24 @@ static void CorrectDCValues(const VP8EncIterator* const it,
// as top[]/left[] on the next block.
int ch;
for (ch = 0; ch <= 1; ++ch) {
const int16_t* const top = it->top_derr_[it->x_][ch];
const int16_t* const left = it->left_derr_[ch];
const int8_t* const top = it->top_derr_[it->x_][ch];
const int8_t* const left = it->left_derr_[ch];
int16_t (* const c)[16] = &tmp[ch * 4];
int err0, err1, err2, err3;
c[0][0] += C1 * top[0] + C2 * left[0];
c[0][0] += (C1 * top[0] + C2 * left[0]) >> (DSHIFT - DSCALE);
err0 = QuantizeSingle(&c[0][0], mtx);
c[1][0] += C1 * top[1] + C2 * err0;
c[1][0] += (C1 * top[1] + C2 * err0) >> (DSHIFT - DSCALE);
err1 = QuantizeSingle(&c[1][0], mtx);
c[2][0] += C1 * err0 + C2 * left[1];
c[2][0] += (C1 * err0 + C2 * left[1]) >> (DSHIFT - DSCALE);
err2 = QuantizeSingle(&c[2][0], mtx);
c[3][0] += C1 * err1 + C2 * err2;
c[3][0] += (C1 * err1 + C2 * err2) >> (DSHIFT - DSCALE);
err3 = QuantizeSingle(&c[3][0], mtx);
rd->derr[ch][0] = err1;
rd->derr[ch][1] = err2;
rd->derr[ch][2] = err3;
// error 'err' is bounded by mtx->q_[0] which is 132 at max. Hence
// err >> DSCALE will fit in an int8_t type if DSCALE>=1.
assert(abs(err1) <= 127 && abs(err2) <= 127 && abs(err3) <= 127);
rd->derr[ch][0] = (int8_t)err1;
rd->derr[ch][1] = (int8_t)err2;
rd->derr[ch][2] = (int8_t)err3;
}
}
@ -885,18 +889,19 @@ static void StoreDiffusionErrors(VP8EncIterator* const it,
const VP8ModeScore* const rd) {
int ch;
for (ch = 0; ch <= 1; ++ch) {
int16_t* const top = it->top_derr_[it->x_][ch];
int16_t* const left = it->left_derr_[ch];
left[0] = rd->derr[ch][0]; // restore err1
left[1] = rd->derr[ch][2]; // ... err3
top[0] = rd->derr[ch][1]; // ... err2
top[1] = rd->derr[ch][2]; // ... err3.
int8_t* const top = it->top_derr_[it->x_][ch];
int8_t* const left = it->left_derr_[ch];
left[0] = rd->derr[ch][0]; // restore err1
left[1] = 3 * rd->derr[ch][2] >> 2; // ... 3/4th of err3
top[0] = rd->derr[ch][1]; // ... err2
top[1] = rd->derr[ch][2] - left[1]; // ... 1/4th of err3.
}
}
#undef C1
#undef C2
#undef DSHIFT
#undef DSCALE
//------------------------------------------------------------------------------

6
src/enc/vp8i_enc.h
View File

@ -121,7 +121,7 @@ static WEBP_INLINE int QUANTDIV(uint32_t n, uint32_t iQ, uint32_t B) {
// #define DISABLE_TOKEN_BUFFER
// quality below which error-diffusion is enabled
#define ERROR_DIFFUSION_QUALITY 30
#define ERROR_DIFFUSION_QUALITY 98
//------------------------------------------------------------------------------
// Headers
@ -204,7 +204,7 @@ typedef struct {
score_t i4_penalty_; // penalty for using Intra4
} VP8SegmentInfo;
typedef int16_t DError[2 /* u/v */][2 /* top or left */];
typedef int8_t DError[2 /* u/v */][2 /* top or left */];
// Handy transient struct to accumulate score and info during RD-optimization
// and mode evaluation.
@ -218,7 +218,7 @@ typedef struct {
uint8_t modes_i4[16]; // mode numbers for intra4 predictions
int mode_uv; // mode number of chroma prediction
uint32_t nz; // non-zero blocks
int16_t derr[2][3]; // DC diffusion errors for U/V for blocks #1/2/3
int8_t derr[2][3]; // DC diffusion errors for U/V for blocks #1/2/3
} VP8ModeScore;
// Iterator structure to iterate through macroblocks, pointing to the