GNOME Bugzilla – Bug 757069
Auto-stretch contrast should operate on linear RGB.
Last modified: 2015-11-21 02:41:37 UTC
Created attachment 314030 [details] [review] Patch to make auto-stretch contrast work by default on linear RGB. Auto-stretch contrast is the equivalent of setting the Levels Value channel white and black points to stretch or compress the dynamic range of the image to fit within 0.0f and 1.0f. On the one hand, setting the white point works about the same (probably exactly the same) on perceptually uniform and linear RGB, although of course the *amount* of the required adjustment varies depending on whether the operation is done on linear or perceptually uniform RGB. On the other hand, setting the black point on perceptually uniform RGB introduces tonality and saturation artifacts: * On a low-saturation image, the differences aren't very noticeable. * The higher the saturation of the original image, the more distorted are the results of operating on perceptually uniform RGB. * For images with out of gamut RGB values, auto-stretch contrast performed on perceptually uniform RGB produces extreme tonality and saturation distortion. To help users get the right results without having to change precision and use the gamma hack, the default for auto-stretch contrast should be to operate on linear RGB.
Created attachment 314031 [details] Illustration showing that auto-stretch contrast should default to linear RGB.
commit a9f56120324585aa24ebec455fa2be5b3ba9d985 Author: Elle Stone <ellestone@ninedegreesbelow.com> Date: Sat Oct 24 13:02:48 2015 -0400 Make auto-stretch contrast operate on linear RGB.