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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
Download Patch File Download Diff File Expand all files Collapse all files

19
src/dec/vp8l.c
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@ -481,7 +481,8 @@ static void ConvertToYUVA(const uint32_t* const src, int width, int y_pos,
uint8_t* const y = buf->y + y_pos * buf->y_stride;
for (i = 0; i < width; ++i) {
const uint32_t p = src[i];
y[i] = VP8RGBToY((p >> 16) & 0xff, (p >> 8) & 0xff, (p >> 0) & 0xff);
y[i] = VP8RGBToY((p >> 16) & 0xff, (p >> 8) & 0xff, (p >> 0) & 0xff,
YUV_HALF);
}
}
@ -500,11 +501,11 @@ static void ConvertToYUVA(const uint32_t* const src, int width, int y_pos,
const int g = ((v0 >> 7) & 0x1fe) + ((v1 >> 7) & 0x1fe);
const int b = ((v0 << 1) & 0x1fe) + ((v1 << 1) & 0x1fe);
if (!(y_pos & 1)) { // even lines: store values
u[i] = VP8RGBToU(r, g, b);
v[i] = VP8RGBToV(r, g, b);
u[i] = VP8RGBToU(r, g, b, YUV_HALF << 2);
v[i] = VP8RGBToV(r, g, b, YUV_HALF << 2);
} else { // odd lines: average with previous values
const int tmp_u = VP8RGBToU(r, g, b);
const int tmp_v = VP8RGBToV(r, g, b);
const int tmp_u = VP8RGBToU(r, g, b, YUV_HALF << 2);
const int tmp_v = VP8RGBToV(r, g, b, YUV_HALF << 2);
// Approximated average-of-four. But it's an acceptable diff.
u[i] = (u[i] + tmp_u + 1) >> 1;
v[i] = (v[i] + tmp_v + 1) >> 1;
@ -516,11 +517,11 @@ static void ConvertToYUVA(const uint32_t* const src, int width, int y_pos,
const int g = (v0 >> 6) & 0x3fc;
const int b = (v0 << 2) & 0x3fc;
if (!(y_pos & 1)) { // even lines
u[i] = VP8RGBToU(r, g, b);
v[i] = VP8RGBToV(r, g, b);
u[i] = VP8RGBToU(r, g, b, YUV_HALF << 2);
v[i] = VP8RGBToV(r, g, b, YUV_HALF << 2);
} else { // odd lines (note: we could just skip this)
const int tmp_u = VP8RGBToU(r, g, b);
const int tmp_v = VP8RGBToV(r, g, b);
const int tmp_u = VP8RGBToU(r, g, b, YUV_HALF << 2);
const int tmp_v = VP8RGBToV(r, g, b, YUV_HALF << 2);
u[i] = (u[i] + tmp_u + 1) >> 1;
v[i] = (v[i] + tmp_v + 1) >> 1;
}