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lossy decoding: correct alpha-rescaling for YUVA format

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The luminance needs to be pre- and post- multiplied by
the alpha value in case of rescaling, for proper averaging.

Also:
- removed util/alpha_processing and moved it to dsp/
- removed WebPInitPremultiply() which was mostly useless
and merged it with the new function WebPInitAlphaProcessing()

Change-Id: If089cefd4ec53f6880a791c476fb1c7f7c5a8e60
This commit is contained in:
skal
2014-05-26 18:05:03 +02:00
committed by Gerrit Code Review
parent 78c12ed8e6
commit 399b916d27
14 changed files with 193 additions and 227 deletions
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120
src/dsp/upsampling.c
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@ -183,92 +183,6 @@ const WebPYUV444Converter WebPYUV444Converters[MODE_LAST] = {
Yuv444ToRgba4444 // MODE_rgbA_4444
};
//------------------------------------------------------------------------------
// Premultiplied modes
// non dithered-modes
// (x * a * 32897) >> 23 is bit-wise equivalent to (int)(x * a / 255.)
// for all 8bit x or a. For bit-wise equivalence to (int)(x * a / 255. + .5),
// one can use instead: (x * a * 65793 + (1 << 23)) >> 24
#if 1 // (int)(x * a / 255.)
#define MULTIPLIER(a) ((a) * 32897UL)
#define PREMULTIPLY(x, m) (((x) * (m)) >> 23)
#else // (int)(x * a / 255. + .5)
#define MULTIPLIER(a) ((a) * 65793UL)
#define PREMULTIPLY(x, m) (((x) * (m) + (1UL << 23)) >> 24)
#endif
static void ApplyAlphaMultiply(uint8_t* rgba, int alpha_first,
int w, int h, int stride) {
while (h-- > 0) {
uint8_t* const rgb = rgba + (alpha_first ? 1 : 0);
const uint8_t* const alpha = rgba + (alpha_first ? 0 : 3);
int i;
for (i = 0; i < w; ++i) {
const uint32_t a = alpha[4 * i];
if (a != 0xff) {
const uint32_t mult = MULTIPLIER(a);
rgb[4 * i + 0] = PREMULTIPLY(rgb[4 * i + 0], mult);
rgb[4 * i + 1] = PREMULTIPLY(rgb[4 * i + 1], mult);
rgb[4 * i + 2] = PREMULTIPLY(rgb[4 * i + 2], mult);
}
}
rgba += stride;
}
}
#undef MULTIPLIER
#undef PREMULTIPLY
// rgbA4444
#define MULTIPLIER(a) ((a) * 0x1111) // 0x1111 ~= (1 << 16) / 15
static WEBP_INLINE uint8_t dither_hi(uint8_t x) {
return (x & 0xf0) | (x >> 4);
}
static WEBP_INLINE uint8_t dither_lo(uint8_t x) {
return (x & 0x0f) | (x << 4);
}
static WEBP_INLINE uint8_t multiply(uint8_t x, uint32_t m) {
return (x * m) >> 16;
}
static WEBP_INLINE void ApplyAlphaMultiply4444(uint8_t* rgba4444,
int w, int h, int stride,
int rg_byte_pos /* 0 or 1 */) {
while (h-- > 0) {
int i;
for (i = 0; i < w; ++i) {
const uint32_t rg = rgba4444[2 * i + rg_byte_pos];
const uint32_t ba = rgba4444[2 * i + (rg_byte_pos ^ 1)];
const uint8_t a = ba & 0x0f;
const uint32_t mult = MULTIPLIER(a);
const uint8_t r = multiply(dither_hi(rg), mult);
const uint8_t g = multiply(dither_lo(rg), mult);
const uint8_t b = multiply(dither_hi(ba), mult);
rgba4444[2 * i + rg_byte_pos] = (r & 0xf0) | ((g >> 4) & 0x0f);
rgba4444[2 * i + (rg_byte_pos ^ 1)] = (b & 0xf0) | a;
}
rgba4444 += stride;
}
}
#undef MULTIPLIER
static void ApplyAlphaMultiply_16b(uint8_t* rgba4444,
int w, int h, int stride) {
#ifdef WEBP_SWAP_16BIT_CSP
ApplyAlphaMultiply4444(rgba4444, w, h, stride, 1);
#else
ApplyAlphaMultiply4444(rgba4444, w, h, stride, 0);
#endif
}
void (*WebPApplyAlphaMultiply)(uint8_t*, int, int, int, int);
void (*WebPApplyAlphaMultiply4444)(uint8_t*, int, int, int);
//------------------------------------------------------------------------------
// Main calls
@ -284,6 +198,10 @@ void WebPInitUpsamplers(void) {
WebPUpsamplers[MODE_ARGB] = UpsampleArgbLinePair;
WebPUpsamplers[MODE_RGBA_4444] = UpsampleRgba4444LinePair;
WebPUpsamplers[MODE_RGB_565] = UpsampleRgb565LinePair;
WebPUpsamplers[MODE_rgbA] = UpsampleRgbaLinePair;
WebPUpsamplers[MODE_bgrA] = UpsampleBgraLinePair;
WebPUpsamplers[MODE_Argb] = UpsampleArgbLinePair;
WebPUpsamplers[MODE_rgbA_4444] = UpsampleRgba4444LinePair;
// If defined, use CPUInfo() to overwrite some pointers with faster versions.
if (VP8GetCPUInfo != NULL) {
@ -302,33 +220,3 @@ void WebPInitUpsamplers(void) {
}
//------------------------------------------------------------------------------
extern void WebPInitPremultiplySSE2(void);
extern void WebPInitPremultiplyNEON(void);
void WebPInitPremultiply(void) {
WebPApplyAlphaMultiply = ApplyAlphaMultiply;
WebPApplyAlphaMultiply4444 = ApplyAlphaMultiply_16b;
#ifdef FANCY_UPSAMPLING
WebPUpsamplers[MODE_rgbA] = UpsampleRgbaLinePair;
WebPUpsamplers[MODE_bgrA] = UpsampleBgraLinePair;
WebPUpsamplers[MODE_Argb] = UpsampleArgbLinePair;
WebPUpsamplers[MODE_rgbA_4444] = UpsampleRgba4444LinePair;
if (VP8GetCPUInfo != NULL) {
#if defined(WEBP_USE_SSE2)
if (VP8GetCPUInfo(kSSE2)) {
WebPInitPremultiplySSE2();
}
#endif
#if defined(WEBP_USE_NEON)
if (VP8GetCPUInfo(kNEON)) {
WebPInitPremultiplyNEON();
}
#endif
}
#endif // FANCY_UPSAMPLING
}
//------------------------------------------------------------------------------