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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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29
src/dsp/dsp.h
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@ -218,12 +218,14 @@ typedef void (*WebPYUV444Converter)(const uint8_t* y,
extern const WebPYUV444Converter WebPYUV444Converters[/* MODE_LAST */];
// Main functions to be called
// Must be called before using the WebPUpsamplers[] (and for premultiplied
// colorspaces like rgbA, rgbA4444, etc)
void WebPInitUpsamplers(void);
// Must be called before using WebPSamplers[]
void WebPInitSamplers(void);
//------------------------------------------------------------------------------
// Pre-multiply planes with alpha values
// Utilities for processing transparent channel.
// Apply alpha pre-multiply on an rgba, bgra or argb plane of size w * h.
// alpha_first should be 0 for argb, 1 for rgba or bgra (where alpha is last).
@ -234,10 +236,27 @@ extern void (*WebPApplyAlphaMultiply)(
extern void (*WebPApplyAlphaMultiply4444)(
uint8_t* rgba4444, int w, int h, int stride);
// To be called first before using the above.
void WebPInitPremultiply(void);
// Pre-Multiply operation transforms x into x * A / 255 (where x=Y,R,G or B).
// Un-Multiply operation transforms x into x * 255 / A.
//------------------------------------------------------------------------------
// Pre-Multiply or Un-Multiply (if 'inverse' is true) argb values in a row.
extern void (*WebPMultARGBRow)(uint32_t* const ptr, int width, int inverse);
// Same a WebPMultARGBRow(), but for several rows.
void WebPMultARGBRows(uint8_t* ptr, int stride, int width, int num_rows,
int inverse);
// Same for a row of single values, with side alpha values.
extern void (*WebPMultRow)(uint8_t* const ptr, const uint8_t* const alpha,
int width, int inverse);
// Same a WebPMultRow(), but for several 'num_rows' rows.
void WebPMultRows(uint8_t* ptr, int stride,
const uint8_t* alpha, int alpha_stride,
int width, int num_rows, int inverse);
// To be called first before using the above.
void WebPInitAlphaProcessing(void);
#ifdef __cplusplus
} // extern "C"