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Update webp container spec with alpha filter options.

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Change-Id: I032f350c8c698aeb139f7dd148f01a0a3b012b6d
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Urvang Joshi 2012-01-12 05:19:22 +00:00 committed by James Zern
parent 2e74ec8b5f
commit dba37fea0e
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: The contents of such a chunk are as follows:
* Byte 0: The _compression method_ used. Currently two methods are * Byte 0 lower nibble: The _compression method_ used. Currently two methods
supported: are supported:
* 0 --> No compression * 0 --> No compression
* 1 --> Backward reference counts encoded with arithmetic encoder. * 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 1: _Reserved_. **Should** be 0.
* Byte 2 onwards: _Encoded alpha bitstream_. * Byte 2 onwards: _Encoded alpha bitstream_.