Binary compatibility of 0.1.3 generated webp with alpha support?

[GoogleCodeExporter]

What steps will reproduce the problem?
1. get 0.1.3 generated webp file
2. try to convert it to png: dwebp test.webp -o test.png
3.

What is the expected output? What do you see instead?
It should convert webp with alpha channel. But the new version (0.2.x) doesn't 
recognize the alpha channel in this old 0.1.3 generated webp. Is it possible to 
read this version with new one? i have millions of this files, i cannot simple 
convert it ;)

What version of the product are you using? On what operating system?
0.1.3 (SHA-1: 817c9dce61f49d9920a5a8eb399aca701522ec11) and 0.2.1 (head)

Please provide any additional information below.

Original issue reported on code.google.com by remo.eic...@gmail.com on 18 Jan 2013 at 10:18

[GoogleCodeExporter]

Sorry i mean this encoder version: WebPGetEncoderVersion() -> 0x00000103

Original comment by remo.eic...@gmail.com on 18 Jan 2013 at 12:19

[GoogleCodeExporter]

Alpha support in 0.1.3 was highly experimental (and less efficient than the 
final version).

Best is really to recompile a dwebp from 0.1.3 and re-convert the files to the 
new definitive format.

Original comment by pascal.m...@gmail.com on 18 Jan 2013 at 3:05

[GoogleCodeExporter]

But then i need to convert with old code from webp to png and then with a new 
version from png to webp? Or is there a better variant?

Original comment by remo.eic...@gmail.com on 18 Jan 2013 at 3:10

[GoogleCodeExporter]

assuming you have dwebp built from 0.1.3 and cwebp built from latest version 
0.2.1, you could do:

dwebp_0.1.3 old_file.webp -o foo.png && cwebp_0.2.1 foo.png -o new_file.webp 
${opts}

where $opts is the options you once used to compressed the old_file.webp (-q 80 
etc...)

This is a re-encoding of an already compressed file, but it should be fairly 
harmless regarding degradation, if you use the same encoding options $opts.

Original comment by pascal.m...@gmail.com on 18 Jan 2013 at 10:39

[GoogleCodeExporter]

Thanks, but the new 0.2.x reads the old format 0.1.x without alpha support. Is 
it possible to extract the alpha channel from the 0.1.x format and merge the 
0.1.x RGB picture (without any recompression) to a new 0.2.x webp image?

I didn't find any working version information of a 0.1.x webp binary data to 
recognize an old version of webp image file. Is this correct?

Original comment by remo.eic...@gmail.com on 21 Feb 2013 at 8:25

[GoogleCodeExporter]

Seems like a too old problem.
If this is still an issue, please re-open.

Original comment by pascal.m...@gmail.com on 19 Aug 2014 at 12:51

• Changed state: WontFix