Look at this picture of the dalai lama. Now scale it down to 50% size using any image manipulation software. If you see an all grey square like below, your photo manipulation program has the bug. So far I tested microsoft office picture manager and it has the bug.
There is an important error in most photography scaling algorithms. All software tested have 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. These exceptions have subsequently been reported: the Netpbm toolkit for graphic manipulations, the developping GEGL toolkit, 32 bit encoded images in Photoshop CS3, the latest version of Image Analyzer, the image exporters in Aperture 1.5.6, the latest version of Rendera, Adobe Lightroom 1.4.1, Pixelmator for Mac OS X, Paint Shop Pro X2 and the Preview app in Mac OS X starting from version 10.6.
in reference to: Gamma error in picture scaling (view on Google Sidewiki)