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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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25
src/enc/picture.c
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@ -16,7 +16,6 @@
#include <math.h>
#include "./vp8enci.h"
#include "../utils/alpha_processing.h"
#include "../utils/random.h"
#include "../utils/rescaler.h"
#include "../utils/utils.h"
@ -402,24 +401,15 @@ static void RescalePlane(const uint8_t* src,
}
static void AlphaMultiplyARGB(WebPPicture* const pic, int inverse) {
uint32_t* ptr = pic->argb;
int y;
for (y = 0; y < pic->height; ++y) {
WebPMultARGBRow(ptr, pic->width, inverse);
ptr += pic->argb_stride;
}
assert(pic->argb != NULL);
WebPMultARGBRows((uint8_t*)pic->argb, pic->argb_stride * sizeof(*pic->argb),
pic->width, pic->height, inverse);
}
static void AlphaMultiplyY(WebPPicture* const pic, int inverse) {
const uint8_t* ptr_a = pic->a;
if (ptr_a != NULL) {
uint8_t* ptr_y = pic->y;
int y;
for (y = 0; y < pic->height; ++y) {
WebPMultRow(ptr_y, ptr_a, pic->width, inverse);
ptr_y += pic->y_stride;
ptr_a += pic->a_stride;
}
if (pic->a != NULL) {
WebPMultRows(pic->y, pic->y_stride, pic->a, pic->a_stride,
pic->width, pic->height, inverse);
}
}
@ -455,6 +445,7 @@ int WebPPictureRescale(WebPPicture* pic, int width, int height) {
}
// If present, we need to rescale alpha first (for AlphaMultiplyY).
if (pic->a != NULL) {
WebPInitAlphaProcessing();
RescalePlane(pic->a, prev_width, prev_height, pic->a_stride,
tmp.a, width, height, tmp.a_stride, work, 1);
}
@ -495,6 +486,7 @@ int WebPPictureRescale(WebPPicture* pic, int width, int height) {
// In order to correctly interpolate colors, we need to apply the alpha
// weighting first (black-matting), scale the RGB values, and remove
// the premultiplication afterward (while preserving the alpha channel).
WebPInitAlphaProcessing();
AlphaMultiplyARGB(pic, 0);
RescalePlane((const uint8_t*)pic->argb, prev_width, prev_height,
pic->argb_stride * 4,
@ -1367,4 +1359,3 @@ LOSSLESS_ENCODE_FUNC(WebPEncodeLosslessBGRA, WebPPictureImportBGRA)
#undef LOSSLESS_ENCODE_FUNC
//------------------------------------------------------------------------------