News for hackers. Stuff that matters.

A comment on JPEG XL. Parent comment

Re:JPEG XL by jonsneyers on Monday June 21, 2021 @02:44PM (#27582456)
Nothing went wrong there, it's just what you get if you configure an encoder using just some quantization setting and not a visual target. The same will happen if you would encode images with libjpeg quality 50 (and then derive all other bitrates from there). In some cases the image will look OK-ish at that setting, in other cases it will be complete garbage.

JPEG XL is the first codec to have a practical encoder that can be configured by saying "I want the worst visual difference to be X units of just-noticeable-difference". All other encoders are basically configured by saying "I want to use this scaling factor for the quantization tables, and let's hope that the result will look OK".

[ Parent | on HN ]
Re:JPEG XL by astrange on Monday June 21, 2021 @05:41PM (#27584890)
> All other encoders are basically configured by saying "I want to use this scaling factor for the quantization tables, and let's hope that the result will look OK".

crf in x264/x265 is smarter than that, but it's still a closed-form solution. That's probably easier to work with than optimizing for constant SSIM or whatever, it always takes one pass and those objective metrics are not actually very good.

[ Parent | on HN ]