Labels: Type-Defect Priority-Medium
New issue 535 by sand...@gmail.com
: Losslessly compressing the attached PNG produces a broken filehttps://bugs.chromium.org/p/webp/issues/detail?id=535
What steps will reproduce the problem?
1. Compress attached cut_x_lef.png with `cwebp -z 9 cut_x_lef.png -o cut_x_lef.webp`
What is the expected output? What do you see instead?
Expected output is a valid lossless WebP image.
Instead, the resulting image uses the color indexing transform twice. This is not allowed per the specification: "Each transform is allowed to be used only once."
I have attached the resulting image I get.
What version of the product are you using? On what operating system?
Version 1.2.0. I also tested latest git as of commit c5bc3624 and the issue also occurs with it.
Operating system is Windows 10 21H1.
Please provide any additional information below.
I noticed the issue because FFmpeg's lossless WebP decoder validates that transforms
are only used once and rejects images which use the same transform multiple times:https://github.com/FFmpeg/FFmpeg/blob/82123e133db6d556f3366a1cbb4f0439d70539d4/libavcodec/webp.c#L1130-L1135
cut_x_lef.png 18.1 KB
cut_x_lef.webp 194 bytes
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