Issue 555 in webp: Webp has Yellow Tint on Scanned Images Produced with GIMP/XnConvert

[flint… via monorail]

Status: New
Owner: ----
Labels: Type-Defect Priority-Medium

New issue 555 by flint...@gmail.com: Webp has Yellow Tint on Scanned Images Produced with GIMP/XnConvert
https://bugs.chromium.org/p/webp/issues/detail?id=555

What steps will reproduce the problem?

The PNG for comparison is uploaded to Google Group conversation :
https://groups.google.com/a/webmproject.org/g/webp-discuss/c/NDbo1APIxQ0

Direct image link:
https://groups.google.com/a/webmproject.org/group/webp-discuss/attach/343fab42184df/1%20Ori%20PNG.png?part=0.2&view=1

1. Convert the original png to jpg-q75 & webp-q90
2. Using GIMP 2.10.80 (My Version) or XnConvert 1.92 x64
3. Open all those images with image viewers/GIMP to compare by alt-tabbing OR switching layers

What is the expected output? What do you see instead?

At webp-q90, obvious Yellow tint & discoloration (Darker/greyed out) was found.
Where jpg-q75 (~roughly same file sizes as webp-q90) performed much better, making much less obvious compression distortion.

Tried using lossless and the problem was
Personally, the only reason I am using webp at all, is because it was supposed to have higher compression capabilities, meaning smaller file sizes given the same image quality. However, this proves to be not always the case.


What version of the product are you using? On what operating system?
Win10x64 1809
GIMP 2.10.80
XnConvert 1.92 x64

Please provide any additional information below.
As an passer-by to image format technologies, I guess that may have to do with the color dot matrices of scanned images?? Pure guessing.

Attachments:
1 Ori PNG.png 3.1 MB
2 JPG at 75.jpg 687 KB
3 Webp at 90.webp 763 KB

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[flint… via monorail]

Comment #1 on issue 555 by flint...@gmail.com: Webp has Yellow Tint on Scanned Images Produced with GIMP/XnConvert
https://bugs.chromium.org/p/webp/issues/detail?id=555#c1

Tried using lossless and the problem was *fixed

[jz… via monorail]

Comment #2 on issue 555 by jz...@google.com: Webp has Yellow Tint on Scanned Images Produced with GIMP/XnConvert
https://bugs.chromium.org/p/webp/issues/detail?id=555#c2

Thanks for filing the bug. The main difference between the jpeg and webp is that for webp the image was subsampled to YUV4:2:0 as this is all lossy supports; the jpeg is 444. If you use 420 for jpeg you'll see something similar (cjpeg -sample 2x2 ... / convert -sampling-factor 2x2 ...).

The -sharp_yuv option will help here [1].

[1] https://developers.google.com/speed/webp/docs/cwebp#lossy_options

[jz… via monorail]

Updates:
Status: WontFix

Comment #3 on issue 555 by jz...@google.com: Webp has Yellow Tint on Scanned Images Produced with GIMP/XnConvert
https://bugs.chromium.org/p/webp/issues/detail?id=555#c3

Closing this as there's no action to take currently. As mentioned -sharp_yuv should help somewhat, it isn't enabled by default due to the increase in processing time and that it is only beneficial on a subset of images.