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Use deterministic random-dithering during RGB->YUV conversion

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-> helps debanding (sky, gradients, etc.)

This dithering can only be triggered when using -preset photo
or -pre 2 (as a preprocessing). Everything is unchanged otherwise.

Note that this change is likely to make the perceived PSNR/SSIM drop
since we're altering the input internally.

Change-Id: Id8d4326245d9b828141de162c94ba381b1fa5813
This commit is contained in:
skal
2013-10-17 22:36:49 +02:00
parent 8a2fa099cc
commit 0b2b05049f
7 changed files with 136 additions and 43 deletions
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33
src/dsp/yuv.h
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@ -265,27 +265,27 @@ extern void VP8YUVInitSSE2(void);
//------------------------------------------------------------------------------
// RGB -> YUV conversion
static WEBP_INLINE int VP8ClipUV(int v) {
v = (v + (257 << (YUV_FIX + 2 - 1))) >> (YUV_FIX + 2);
return ((v & ~0xff) == 0) ? v : (v < 0) ? 0 : 255;
// Stub functions that can be called with various rounding values:
static WEBP_INLINE int VP8ClipUV(int uv, int rounding) {
uv = (uv + rounding + (128 << (YUV_FIX + 2))) >> (YUV_FIX + 2);
return ((uv & ~0xff) == 0) ? uv : (uv < 0) ? 0 : 255;
}
#ifndef USE_YUVj
static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
const int kRound = (1 << (YUV_FIX - 1)) + (16 << YUV_FIX);
static WEBP_INLINE int VP8RGBToY(int r, int g, int b, int rounding) {
const int luma = 16839 * r + 33059 * g + 6420 * b;
return (luma + kRound) >> YUV_FIX; // no need to clip
return (luma + rounding + (16 << YUV_FIX)) >> YUV_FIX; // no need to clip
}
static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
static WEBP_INLINE int VP8RGBToU(int r, int g, int b, int rounding) {
const int u = -9719 * r - 19081 * g + 28800 * b;
return VP8ClipUV(u);
return VP8ClipUV(u, rounding);
}
static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
static WEBP_INLINE int VP8RGBToV(int r, int g, int b, int rounding) {
const int v = +28800 * r - 24116 * g - 4684 * b;
return VP8ClipUV(v);
return VP8ClipUV(v, rounding);
}
#else
@ -293,20 +293,19 @@ static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
// This JPEG-YUV colorspace, only for comparison!
// These are also 16bit precision coefficients from Rec.601, but with full
// [0..255] output range.
static WEBP_INLINE int VP8RGBToY(int r, int g, int b) {
const int kRound = (1 << (YUV_FIX - 1));
static WEBP_INLINE int VP8RGBToY(int r, int g, int b, int rounding) {
const int luma = 19595 * r + 38470 * g + 7471 * b;
return (luma + kRound) >> YUV_FIX; // no need to clip
return (luma + rounding) >> YUV_FIX; // no need to clip
}
static WEBP_INLINE int VP8RGBToU(int r, int g, int b) {
static WEBP_INLINE int VP8_RGB_TO_U(int r, int g, int b, int rounding) {
const int u = -11058 * r - 21710 * g + 32768 * b;
return VP8ClipUV(u);
return VP8ClipUV(u, rounding);
}
static WEBP_INLINE int VP8RGBToV(int r, int g, int b) {
static WEBP_INLINE int VP8_RGB_TO_V(int r, int g, int b, int rounding) {
const int v = 32768 * r - 27439 * g - 5329 * b;
return VP8ClipUV(v);
return VP8ClipUV(v, rounding);
}
#endif // USE_YUVj