jpeg artifacts

[pklat]

I must edit+recompress jpegs. They are magazine scans, relatively lores 800x1200. I'd like to use avif.
Should I use some filters to remove artifacts/noise first?

[dot]

Avif is a mixed bag in my experience, sometimes its really efficient, sometimes its not that good and its beaten by heif (with aq-mode 3+) or even new jpeg-xl, it depends on input I guess.
Iirc Gimp has a plugin/script to clean up scans, I forget how its called
You could use this for images of quality 90 or lower or alternatively knusperli

[Trench]

This one fixed artifacts and makes pics better than original if you see the examples but you only have a few tries and you have to choose one of the 4 options to make it work
https://letsenhance.io/


another odd one is XBRZ which is for pixels
https://sourceforge.net/projects/xbrz/

Another is just to look at tutorials online.

[zubzer0]

https://github.com/google/knusperli
easy deblocking. it will work well if the original is compressed in q80-90

https://github.com/ilyakurdyukov/jpeg-quantsmooth
deblock and remove artifact for q40-80

https://github.com/victorvde/jpeg2png
very strong deblock and remove artifact for < q40

All three operate with DCT, so if the image was saved first in q40 and then in q90, then these programs will not help you.

[Jaff]

I must edit+recompress jpegs. They are magazine scans, relatively lores 800x1200. I'd like to use avif.
Should I use some filters to remove artifacts/noise first?

You can use Better JPEG (Photoshop plugin) to recompress only the edited areas of images (if you want to preserve as much as possible original image)
Also, for denoise you may try the following Photoshop plugins: AQuaDenoise / NeatImage or standalone program: Topaz JPEG to RAW AI

In your place, I'll go with a PDF conversion (ABBYY FineReader) in a DJVU style (separated text from background images) or direct DJVU conversion.