bug#74476: [PATCH] Explore JPEG loading without quantization

[Eli Zaretskii]

> Date: Fri, 22 Nov 2024 15:53:18 +0100
> From:  Manuel Giraud via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> While trying to speed up "emacs as an image viewer", I found that emacs
> is using libjpeg with color quantization and it seems that removing this
> quantization could speed up JPEG loading a bit.
> 
> My simple limited benchmark:
> 
>           - M-: (clear-image-cache)
>           - Open an image in folder with some large enough pictures in
>             it (4000x3000 here)
>           - M-: (benchmark-run 10 (image-next-file 1))
> 
> Here are the results I get:
> 
> without this path: (5.415405491 1 0.09232176400000025)
> with: (3.079911418 1 0.0751190459999993)
> 
> I don't think that this patch could be applied as is (it is rather
> ugly).  And I also think that I probably have missed some (many?) use
> case (where color quantization is mandatory).  But I'm submitting this
> patch anyway as a conversation starter on the subject.

Alan, any comments?  I know nothing about this "color quantization"
aspect of JPEG images.