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Merge "Update webp container spec with alpha filter options."

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James Zern 2012-01-13 14:25:39 -08:00 committed by Gerrit Code Review
commit a33842fdb0
1 changed files with 13 additions and 2 deletions
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15
doc/webp-container-spec.txt
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@ -521,13 +521,24 @@ the bit-stream for the Alpha-chunk is still experimental and expected to change.
The contents of such a chunk are as follows:
* Byte 0: The _compression method_ used. Currently two methods are
supported:
* Byte 0 lower nibble: The _compression method_ used. Currently two methods
are supported:
* 0 --> No compression
* 1 --> Backward reference counts encoded with arithmetic encoder.
* Byte 0 upper nibble: The _filtering method_ used. Currently the following
methods are supported:
* 0 --> No filter
* 1 --> Horizontal filter
* 2 --> Vertical filter
* 3 --> Gradient filter
* Byte 1: _Reserved_. **Should** be 0.
* Byte 2 onwards: _Encoded alpha bitstream_.