Is it me or is the ImageMagick "0-100 quality to 1-19 libjxl distance" function a little wonky? (especially for values under 30) gist.github.com/fasterthanli... - ThreadSky

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fasterthanli.me • 30 days ago

Is it me or is the ImageMagick "0-100 quality to 1-19 libjxl distance" function a little wonky? (especially for values under 30)

https://gist.github.com/fasterthanlime/072ff6eedfdb4297929298671a0f629f

Comments

jakobsen.lol•30 days ago

Definitely wonky
https://www.desmos.com/calculator/sqlrfb4xxa

fasterthanli.me•30 days ago

Oh, I got thrown off by the x=0 value I think, which is hardcoded to 1 — this doesn't actually look too bad.

jonsneyers.bsky.social•25 days ago

IIRC, ImageMagick has some weird convention that quality 0 means "default quality" instead of very low quality.

In recent libjxl versions, you can use
JxlEncoderDistanceFromQuality() to do the mapping, maybe IM should switch to that to make sure it uses the same mapping as cjxl.

fasterthanli.me•25 days ago

yeah it does! https://github.com/ImageMagick/ImageMagick/blob/471841b7bf5c373163844ce88ebc50c194d28a0c/coders/jxl.c#L910

fasterthanli.me•30 days ago

Thanks for the graph btw! This is a super nice tool.

jakobsen.lol•30 days ago

No problem! Desmos is really handy, used it a ton in uni

jakobsen.lol•30 days ago

I suppose not, I was just thrown off by the discontinuity at x=0 and the kink at x=30, but for x > 0 it's continuous at least :)

And to be fair, I know nothing about JPEG XL so I have no idea what I'm talking about. Please disregard all opinions and enjoy the picture instead

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