I tried File:Rajpoots_2.png, a 10MP engraving scan which is a subject of bug 24889 about Moiré patterns: https://commons.wikimedia.org/wiki/File:Rajpoots_2.png https://bugzilla.wikimedia.org/show_bug.cgi?id=24889
At the given default settings I think it does a better job than current ImageMagick, while still not perfect: < https://test2.wikipedia.org/wiki/Special:VipsTest?file=Rajpoots_2.png&wi...
< https://test2.wikipedia.org/wiki/Special:VipsTest?file=Rajpoots_2.png&wi...
The sharpening makes the image "pop" a little nicely, but the Moiré pattern is (somewhat) reduced regardless of that setting. Still not nearly as nice as a non-decimated scale down with ImageMagick (which we don't use).
Enabling bilinear filtering causes HUGE HORRIBLE artifacts, and is definitely not a good thing for that sort of image. :) < https://test2.wikipedia.org/wiki/Special:VipsTest?file=Rajpoots_2.png&wi...
< https://test2.wikipedia.org/wiki/Special:VipsTest?file=Rajpoots_2.png&wi...
-- brion