dany/libwebp
1
0
Fork 0
mirror of https://github.com/webmproject/libwebp.git synced 2025-07-12 22:14:29 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity

Mux: Allow only some frames/tiles to have alpha.

Browse Source 
And related const fixes.

Change-Id: I79f6f1b9f8c6faac8cc4ef24b58edff6d90de045
This commit is contained in:
Urvang Joshi
2012-06-29 17:16:08 +05:30
parent 3ba81bbe8b
commit 97649c8f6b
4 changed files with 17 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
doc/webp-container-spec.txt
View File

@ -300,9 +300,7 @@ multiple frames. Data for each frame consists of:
present at the beginning of each tile for a frame that is represented as
multiple tile images.
* An optional 'ALPH' chunk with alpha bitstream of the frame/tile. If the
file contains transparency, this chunk MUST be present for each frame/tile
containing a 'VP8 ' chunk. It MUST NOT be present otherwise.
* An optional 'ALPH' chunk with alpha bitstream of the frame/tile.
* A 'VP8 ' or a 'VP8L' chunk containing compressed image data of the
frame/tile.
@ -355,7 +353,8 @@ Metadata (M): 1 bit
Alpha (L): 1 bit
: Set if the file contains images with transparency information ("alpha").
: Set if the file contains some (or all) images with transparency information
("alpha").
Rotation and Symmetry (R): 3 bits
@ -540,10 +539,10 @@ Alpha bitstream: _Chunk Size_ - `1` bytes
: Encoded alpha bitstream.
This optional chunk contains encoded alpha data for a single frame/tile.
Either **ALL or NONE** of the frame/tiles must contain this chunk. However,
there is one exception to this rule: a frame/tile containing a 'VP8L' chunk
SHOULD NOT contain this chunk. **Rationale**: the transparency information of
a frame/tile is already part of the 'VP8L' chunk.
For images with transparency, some of the frames/tiles may contain this chunk.
However, a frame/tile containing a 'VP8L' chunk SHOULD NOT contain this chunk.
**Rationale**: the transparency information of a frame/tile is already part of
the 'VP8L' chunk.
The alpha channel data is losslessly stored as raw data (when
compression method is '0') or compressed using the lossless format