Version: (using KDE 4.4.0) OS: Linux Installed from: Gentoo Packages Having some pictures which gave strange previews i searched the net and found: http://www.4p8.com/eric.brasseur/gamma.html I downloaded the photograph of His Holiness the Dalai Lama. The preview of this picture shows as grey rectangle (tested in konqueror and dolphin).
Please do note that the example is contrived to fail on algorithms that do not do perfect gamma correction internally (which is much slower). I personally would argue that having slower image scaling to be accurate to a given gamma would most of the time be a negative effect, especially in the context of a web browser. However it is true that most images are handled in a color space using gamma so mis-rendering of images is possible if not gamma-corrected in the colorspace used by the image. From what I understand if the image does not provide the gamma used (or otherwise define it) a good default choice is gamma = 2.2.
Updated link: http://www.ericbrasseur.org/gamma.html