GNOME Bugzilla – Bug 757685
Clone should operate on linear RGB by default.
Last modified: 2016-12-27 02:27:49 UTC
For radiometrically correct color blending, the clone tool needs to operate on linear RGB. This is true of Normal blend mode and also most other blend modes. The exceptions would be "soft light/overlay/hard light" and maybe "difference", and also "grain extract/grain merge" if the mid-point of grain extract/merge is kept at 0.50 instead of changing it to 0.184187 (bug 757485). Currently the clone tool defaults to operating on perceptually uniform RGB, which creates typical gamma blending artifacts, including wrong colors and dark rings around areas of lower-opacity cloning. Currently the only way for users to get correctly blended results is to switch to linear precision. It would be better if cloning defaulted to using linear RGB except for the noted blend modes.
This looks like it could be handled by current WIP by Pippin on the pippin/linear-is-the-new-black branch. Adding Pippin in CC to get his input. :-)
In linear-is-the-new-black, opened JPGs and PNGs end up as linear (and single precision float), thus the default behavior is the correct behavior in that branch.
The clone tool doesn't implement its own paint modes, the code is fully shared with the layer compositing / paint tool - marking as duplicate of bug #757485 *** This bug has been marked as a duplicate of bug 757485 ***