Issue 626 in webp: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.

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lingy… via monorail

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Nov 29, 2023, 10:07:50 PM11/29/23
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Status: New
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Labels: Type-Defect Priority-Medium

New issue 626 by lingy...@gmail.com: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.
https://bugs.chromium.org/p/webp/issues/detail?id=626

What steps will reproduce the problem?
1. use libwebp to process a webp image
2. convert input.webp -quality 97 output97.webp
3. convert input.webp -quality 98 output98.webp
4. convert input.webp -quality 99 output99.webp
5. convert input.webp -quality 100 output100.webp

What is the expected output? What do you see instead?
expected output: output100.webp's size is a little bit larger than output100.webp

actual:
➜ Downloads ls -lh | grep output
-rw-r--r--@ 1 640K 11 30 10:31 output100.webp
-rw-r--r--@ 1 214K 11 30 11:02 output97.webp
-rw-r--r--@ 1 223K 11 30 11:02 output98.webp
-rw-r--r--@ 1 235K 11 30 10:30 output99.webp


What version of the product are you using? On what operating system?

➜ Downloads cwebp -version
1.3.2
libsharpyuv: 0.2.1

Please provide any additional information below.
origin img:
-rw-r--r--@ 1 236K 11 29 19:24 input.webp

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ygu… via monorail

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Nov 30, 2023, 3:49:05 AM11/30/23
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Comment #1 on issue 626 by ygu...@google.com: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.
https://bugs.chromium.org/p/webp/issues/detail?id=626#c1

Thank you for the report.
Could you provide the source image for reproduction please?

lingy… via monorail

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Dec 4, 2023, 8:13:12 AM12/4/23
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Comment #2 on issue 626 by lingy...@gmail.com: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.
https://bugs.chromium.org/p/webp/issues/detail?id=626#c2

https://www.gstatic.com/webp/gallery/1.webp
@ygu...@google.com this image can repro

ygu… via monorail

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Dec 4, 2023, 8:46:22 AM12/4/23
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Updates:
Status: Invalid

Comment #3 on issue 626 by ygu...@google.com: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.
https://bugs.chromium.org/p/webp/issues/detail?id=626#c3

I could not reproduce the issue with libwebp. Using libwebp at commit 89c5b91:

cwebp 1.webp -q 99 -o 1_q99.webp
cwebp 1.webp -q 100 -o 1_q100.webp
ls -l
54844 1_q100.webp
54388 1_q99.webp
30320 1.webp

However I was able to reproduce the issue with ImageMagick convert tool:
196656 output100.webp
59688 output99.webp

WebP is not mentioned at https://imagemagick.org/script/command-line-options.php#quality
but one can read "The default quality value 100, a request for non-lossy compression."
So my guess is that ImageMagick considers 100 to be lossless, not highest-quality lossy,
and the figures above make sense. Either stick to the lossy [0-99] range with ImageMagick
or switch to using the cwebp binary directly for more settings on the WebP compression.

jz… via monorail

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Dec 4, 2023, 2:27:44 PM12/4/23
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Comment #4 on issue 626 by jz...@google.com: When using the -quality 100 parameter to process webp images, the output result size is too large and does not meet expectations.
https://bugs.chromium.org/p/webp/issues/detail?id=626#c4

Thanks for looking into this Yannis. Your analysis is correct, ImageMagick will use lossless with a quality >= 100:

https://github.com/ImageMagick/ImageMagick/blob/9e4f5fcb54cd103f1ae497140533ee5a9f4d714d/coders/webp.c#L1135
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