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Fix bug for Alpha in RGBA_4444 color-mode.

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Fix bug for Alpha data in RGBA_4444 color-mode.
The Alpha data is required to be clipped [0, 15] while
converting from 8 bits to 4 bits.

Change-Id: I80705d575c35121beb9633a05ec8823435c79586
This commit is contained in:
Vikas Arora 2012-01-09 14:05:28 +05:30
parent ad1e163a0d
commit 221a06bb16
1 changed files with 6 additions and 2 deletions
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8
src/dec/io.c
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@ -202,6 +202,10 @@ static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
return 0; return 0;
} }
static WEBP_INLINE uint32_t clip(uint32_t v, uint32_t max_value) {
return (v > max_value) ? max_value : v;
}
static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) { static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
const int mb_w = io->mb_w; const int mb_w = io->mb_w;
const int mb_h = io->mb_h; const int mb_h = io->mb_h;
@ -213,7 +217,7 @@ static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
for (j = 0; j < mb_h; ++j) { for (j = 0; j < mb_h; ++j) {
for (i = 0; i < mb_w; ++i) { for (i = 0; i < mb_w; ++i) {
// Fill in the alpha value (converted to 4 bits). // Fill in the alpha value (converted to 4 bits).
const uint8_t alpha_val = (alpha[i] + 8) >> 4; const uint32_t alpha_val = clip((alpha[i] + 8) >> 4, 15);
dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val; dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val;
} }
alpha += io->width; alpha += io->width;
@ -490,7 +494,7 @@ static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos) {
ExportRow(&p->scaler_a); ExportRow(&p->scaler_a);
for (i = 0; i < p->scaler_a.dst_width; ++i) { for (i = 0; i < p->scaler_a.dst_width; ++i) {
// Fill in the alpha value (converted to 4 bits). // Fill in the alpha value (converted to 4 bits).
const uint8_t alpha_val = (p->scaler_a.dst[i] + 8) >> 4; const uint32_t alpha_val = clip((p->scaler_a.dst[i] + 8) >> 4, 15);
dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val; dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val;
} }
dst += buf->stride; dst += buf->stride;