-pre 4 bug?

[vincent...@gmail.com]

Hi,

Weeks ago I asked about 444 chroma support and Pascal Massimino suggested to set the prefilter to 4 which greatly improved the retention of the small sharp saturated details.

While playing around with different images, I found out that -pre 4 seems to mess up badly the dark tones.  I included some images to illustrate the problem.
Here's the complete command line I used :

cwebp -q 90 -pre 1 -alpha_filter best -alpha_cleanup -alpha_q 75 -m 6 -af -pass 10 -mt webp-test.png -o webp-test-pre1.webp

(alpha parameters are irrelevant with the attached image, but I kept them as I use transparent image often)

Is it a bug or a side effect of this pre-filter?
thanks

[vincent...@gmail.com]

I'm not actively following this group, and I just figured this issue is already discussed here https://groups.google.com/a/webmproject.org/forum/#!topic/webp-discuss/6wMQrupJNAM
Sorry for the duplicate.

[Pascal Massimino]

Hi Vincent,

Are you using the latest github source tree, or the official 0.5.1 release version of cwebp?

Because i think your bug was fixed by these patches [1][2], as seen from the attached output

(this is just your command line ran with HEAD version of cwebp).

hope it helps,

skal/

[1] https://chromium-review.googlesource.com/#/c/383531/

[2] https://chromium-review.googlesource.com/#/c/383651/