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webp-lossless-bitstream-spec: add PredictorTransformOutput

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Describe the addition of the residual value to the predicted value.

Bug: webp:611
Change-Id: Id0300937eeebbafec3b2cd15376c56418c98a3bf
This commit is contained in:
James Zern 2023-06-22 18:44:27 -07:00
parent cd7e02bece
commit 4298e9765c
1 changed files with 14 additions and 0 deletions
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doc/webp-lossless-bitstream-spec.txt
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@ -363,6 +363,20 @@ exceptional. The pixels on the rightmost column are predicted by using the modes
\[0..13\], just like pixels not on the border, but the leftmost pixel on the
same row as the current pixel is instead used as the TR-pixel.
The final pixel value is obtained by adding each channel of the predicted value
to the encoded residual value.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
void PredictorTransformOutput(uint32 residual, uint32 pred,
uint8* alpha, uint8* red,
uint8* green, uint8* blue) {
*alpha = ALPHA(residual) + ALPHA(pred);
*red = RED(residual) + RED(pred);
*green = GREEN(residual) + GREEN(pred);
*blue = BLUE(residual) + BLUE(pred);
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
### 4.2 Color Transform