GNOME Bugzilla – Bug 543810
Use alpha channel for non-transparent information
Last modified: 2008-10-30 20:14:46 UTC
When I use GIMP I sometimes use the alpha channel for things like bump maps, specular maps or even parallax maps and would be good if there was a check box when you right-click the alpha layer that would enable/disable it's use for transparency. This could have the same effect as using the threshold alpha with a setting of 0 while it's disabled. Another way to do it could be if you make the alpha channel invisible it would look like the threshold alpha mentioned above and when only the alpha channel is selected then you could edit and apply effects to the alpha channel as if it were a custom channel. This could apply with all channels but I believe the alpha channel needs this the most.
Hi and thanks for the enhancement request. For reference, this is somewhat related to bug #486902. IMO it would be pretty backwards to disable the use of an alpha channel, a cleaner solution would be to support auxiliary channels in RGB mode. We should sort out the details on the gimp-developer mailing list and open an enhancement request when it is clear how to implement the feature.
I will, but just to be clear I do not wish the removal of any functionality but rather add an option for people who wish to use the alpha channel either separately or for tasks other than to create transparency. Anyway, before I post this on the mailing list can you send me an e-mail describing auxiliary channels and how they work?
As mentioned on the mailing list, it would be a mistake to use the alpha channel for something else than transparency. Instead, the corresponding file plug-ins could be modified to support the non-standard file format that uses the alpha channel to store some unrelated information. The conversion to/from standard layers or channels could happen when loading and saving the files in that format. But that should probably still be discussed on the mailing list, and the outcome (if any) should then be submitted as a new enhancement request.
For docuemtnation purposes: the featrues requested here are available through the use of layers masks. Choose "layer's alpha channel" option when creatign a mask for the desired effect.