Support alternative JPEG quantisation methods

[rhlp]

heya! i noticed that the app is missing jpeg quantization settings! wich kind of sucks.
i thought i would ask for it to be added.

so! heres a quick demo of what changing quantization does to an image.
heres a small part of an image i took in iceland.
on the left is the png image. the right is the image with regular quantisation (whats now in xnconvert)

default.png

and that just looks like squares! but if you change the quantization, you can find other types that work better for your image! (use the site squoosh.app for some examples.) for this image, i changed it to use "ahumada et al" quantization.
and while it's not perfect, you can tell that it's a lot better!

other one.png

i would love to see more jpeg settings added to the app. because there is a lot we are missing! chroma quality settings,
quantization, actually that seems to be it.
but yeah!

have a nice day!
~~~Rose!

singleflower.gif

[user0]

Trellis quantization is a feature of the mozjpeg encoder:

- Trellis quantization. When converting other formats to JPEG it maximizes quality/filesize ratio.
- Comes with new quantization table presets, e.g. tuned for high-resolution displays.

So your suggestion is really "Add mozjpeg encoder", which has been requested already.

However, mozjpeg is not the only way to get better quality per byte, eg Jpegli doesn't use trellis quantization, but pursues the same goal through other means: adaptive quantization, tuned quantization tables and higher-precision internal processing (which also reduces banding).

Encoders comparison
Users prefer Jpegli over same-sized libjpeg-turbo or MozJPEG
JPEG XL and the Pareto Front