There is an error in most photography scaling algorithms. All software tested (August 2007) had the problem: The Gimp, Adobe Photoshop, CinePaint, Nip2, ImageMagick, GQview, Eye of Gnome, Paint and Krita. Also three different operating systems were used: Linux, Mac OS X and Windows. (Software that don’t have the problem are listed in the Solutions chapter.)Photographs that have been scaled with these software have been degradated (see the examples). The degradation is often faint but probably most pictures contain at least an array where the degradation is clearly visible. I suppose this happens since the first versions of these software, maybe 20 years ago.
I tried this with the software I use — the free Photo Toolkit. Yep, it has this flaw too!