Thumbnails of PNG images with indexed colors are converted to true-color thumbnails, which result in a greater file size. Indexed-color PNGs should be converted to indexed color Thumbnails.
For example (a grayscale), the same images (8b) converted (to 16b) is sharper:
http://commons.wikimedia.org/wiki/File:Jürgen_Alberts_-_pv_portrait_02-3.png
Version: unspecified
Severity: normal
URL: http://commons.wikimedia.org/wiki/File:Jürgen_Alberts_-_pv_portrait_02-3.png