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fix the ARGB4444 premultiply arithmetic

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* green was not descaled properly
* alpha was over-dithered, making the value '0x0f' not be a fixed point
* alpha value was not restored ok.

Change-Id: Ia4a4d75bdad41257f7c07ef76a487065ac36fede
This commit is contained in:
Pascal Massimino 2012-08-09 11:32:30 -07:00
parent a0a488554d
commit 528a11af35
1 changed files with 10 additions and 8 deletions
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18
src/dsp/upsampling.c
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@ -271,8 +271,7 @@ static void ApplyAlphaMultiply(uint8_t* rgba, int alpha_first,
// rgbA4444 // rgbA4444
#define MULTIPLIER(a) ((a) * 0x11) #define MULTIPLIER(a) ((a) * 0x1111) // 0x1111 ~= (1 << 16) / 15
#define PREMULTIPLY(x, m) (((x) * (m)) >> 12)
static WEBP_INLINE uint8_t dither_hi(uint8_t x) { static WEBP_INLINE uint8_t dither_hi(uint8_t x) {
return (x & 0xf0) | (x >> 4); return (x & 0xf0) | (x >> 4);
@ -282,24 +281,27 @@ static WEBP_INLINE uint8_t dither_lo(uint8_t x) {
return (x & 0x0f) | (x << 4); return (x & 0x0f) | (x << 4);
} }
static WEBP_INLINE uint8_t multiply(uint8_t x, uint32_t m) {
return (x * m) >> 16;
}
static void ApplyAlphaMultiply4444(uint8_t* rgba4444, static void ApplyAlphaMultiply4444(uint8_t* rgba4444,
int w, int h, int stride) { int w, int h, int stride) {
while (h-- > 0) { while (h-- > 0) {
int i; int i;
for (i = 0; i < w; ++i) { for (i = 0; i < w; ++i) {
const uint8_t a = dither_lo(rgba4444[2 * i + 1]); const uint8_t a = (rgba4444[2 * i + 1] & 0x0f);
const uint32_t mult = MULTIPLIER(a); const uint32_t mult = MULTIPLIER(a);
const uint8_t r = PREMULTIPLY(dither_hi(rgba4444[2 * i + 0]), mult); const uint8_t r = multiply(dither_hi(rgba4444[2 * i + 0]), mult);
const uint8_t g = PREMULTIPLY(dither_lo(rgba4444[2 * i + 0]), mult); const uint8_t g = multiply(dither_lo(rgba4444[2 * i + 0]), mult);
const uint8_t b = PREMULTIPLY(dither_hi(rgba4444[2 * i + 1]), mult); const uint8_t b = multiply(dither_hi(rgba4444[2 * i + 1]), mult);
rgba4444[2 * i + 0] = (r & 0xf0) | (g & 0x0f); rgba4444[2 * i + 0] = (r & 0xf0) | ((g >> 4) & 0x0f);
rgba4444[2 * i + 1] = (b & 0xf0) | a; rgba4444[2 * i + 1] = (b & 0xf0) | a;
} }
rgba4444 += stride; rgba4444 += stride;
} }
} }
#undef MULTIPLIER #undef MULTIPLIER
#undef PREMULTIPLY
void (*WebPApplyAlphaMultiply)(uint8_t*, int, int, int, int) void (*WebPApplyAlphaMultiply)(uint8_t*, int, int, int, int)
= ApplyAlphaMultiply; = ApplyAlphaMultiply;