Bug 228934

Summary: Gamma error in picture scaling
Product: [Frameworks and Libraries] kio-extras Reporter: hoea
Component: Thumbnails and previewsAssignee: Plasma Bugs List <plasma-bugs>
Status: REPORTED ---    
Severity: normal CC: a.samirh78, kdelibs-bugs, konq-bugs, mpyne, nate
Priority: NOR    
Version: unspecified   
Target Milestone: ---   
Platform: Gentoo Packages   
OS: Linux   
URL: http://www.ericbrasseur.org/gamma.html
Latest Commit: Version Fixed In:

Description hoea 2010-02-28 18:43:40 UTC 
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).
Comment 1 Michael Pyne 2010-03-01 00:55:05 UTC 
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.
Comment 2 Christoph Feck 2017-11-15 23:03:56 UTC 
Updated link: http://www.ericbrasseur.org/gamma.html