JPEG images that are scaled down to smaller sizes tend to have significant artifacts. Can the quality setting be made customizable?
How to reproduce:
1. Upload a JPEG image to the wiki.
2. Use the JPEG image in a way that causes a thumbnail to be generated. For example, [[File:Filename.jpg|120px]].
3. Observe the extreme quality loss. An unacceptable amount of JPEG artifacts (blockiness, blurriness, discoloration) are present.
JPEG artifacts are to be expected when using JPEG files, however one would expect a quality setting to be available for the administrator of a MediaWiki installation to specify just how much JPEG artifacting is introduced when scaling images.
In some cases, the quality loss is so bad that we are forced to convert JPEG images to PNG so the images can be thumbnailed properly and used on the wiki.
Here is a comparison we made on our wiki: https://splatoonwiki.org/wiki/User:Heddy/thumbnail_test
We are using MediaWiki 1.30 and ImageMagick is doing the thumbnailing.
Version: ImageMagick 6.8.9-9 Q16 x86_64 2017-07-31 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2014 ImageMagick Studio LLC
Features: DPC Modules OpenMP
Delegates: bzlib cairo djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png rsvg tiff wmf x xml zlib