search

teasame / webp

Automatically exported from code.google.com/p/webp
0 stars 0 forks source link

Better alpha compression #84

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
With images like this one 
(http://upload.wikimedia.org/wikipedia/commons/4/45/Cliparts_%28examples%29.png)
 a considerable percent of bytes go to alpha channel. Have you plans of 
supporting different (like LZMA or some kind of lossy) compression methods ?

Original issue reported on code.google.com by iskes...@gmail.com on 17 Jun 2011 at 11:59

GoogleCodeExporter commented 9 years ago 
This example clipart has indeed a lot of alpha information: 84k (measured by 
using ImageMagick's 'convert -alpha opaque' ).

I've tried compressing with the current HEAD's cwebp at different lossy-ness 
level for alpha.
 The resulting alpha sizes were:

cwebp -alpha_q 70 -> 38669 bytes
cwebp -alpha_q 80 -> 57393 bytes
cwebp -alpha_q 90 -> 65657 bytes
cwebp -alpha_q 100 (ie: lossless) -> 72059 bytes

Note that decompression speed is an important factor too, in addition to just 
the compressed size.

Original comment by pascal.m...@gmail.com on 10 Dec 2011 at 9:01