[Mediawiki-l] Thumbnail compression quality--how does MW set it?

[Ken McDonald]

I'm getting some images where the thumbnail is displaying much more 
artifacting than the original, even though the thumbnail is much smaller 
than the original. Is there a way to fix this, and does anyone know how 
MW determines what compression quality to use when producing thumbnails, 
so I can avoid it in the future?

Thanks,
Ken