All of the following are fewatures I use frequently or wish I could use:
Multiple layers of Undo/Redo. The more the better.
A quick way to convert tiles of a specified size into layers and layers into tiles. This way you can stack frames in an animation or display them side by side. Possibly, this should generate a new image.
Autosave backups. I use the Gimp, and it crashes on me constantly, but even if you manage to construct a stable program, it is nice to know that if you do crash, you will never lose more than a couple minutes of work.
Simple lighting/tinting options with HSV and Brightness/Contrast.
Selection tools should constrict the area affected by tools and other functions. Color picker should probably be immune.
Add/subtract/invert selection.
Transparency and alpha channel support.
At the very least, bmp, png, and gif support, and at least one lossless format capable of storing multiple layers with alpha channel.
Ability to adjust opacity of layers.
Multiple layers of Undo/Redo. The more the better.
A quick way to convert tiles of a specified size into layers and layers into tiles. This way you can stack frames in an animation or display them side by side. Possibly, this should generate a new image.
Autosave backups. I use the Gimp, and it crashes on me constantly, but even if you manage to construct a stable program, it is nice to know that if you do crash, you will never lose more than a couple minutes of work.
Simple lighting/tinting options with HSV and Brightness/Contrast.
Selection tools should constrict the area affected by tools and other functions. Color picker should probably be immune.
Add/subtract/invert selection.
Transparency and alpha channel support.
At the very least, bmp, png, and gif support, and at least one lossless format capable of storing multiple layers with alpha channel.
Ability to adjust opacity of layers.