I like the looseness that comes from indexpainting with a truecolor 'backbuffer' (this is basically how it works in GIMP 2.9) -- you can 'invisibly build up' paint until it passes a threshold and becomes visible.
Please explain. How do you do this in GIMP?
It's actually pretty easy (assuming compilation isn't scary to you
* Compile and install a recent version of GIMP 2.9. Ideally the
very most recent. Installing deps (especially babl and gegl) may be required.
* Launch GIMP and create a new image
* Prepare a palette with the colors you wanna start with.
* Convert the image to indexed with custom palette set to the aforementioned palette. Uncheck the 'remove unused colors' checkbox.
* Paint with anything that isn't pencil tool. Airbrush, or paintbrush with a fuzzy brush, for example.
Experiment with the new Force parameter to get paint coming quicker or slower. Everything is fully functional (eg. use whatever paint mode you want, it'll work)
* Also make sure your painting is using Default, not Legacy, blending (that's controlled by the new widget sitting next to Paint Mode in the
tool options). This isn't strictly required but makes everything much easier to predict.
* Layer modes work as expected, except the result of blending is not indexized before display. IMO this is a bug. Need to merge layer down to fully indexize. Non-binary alpha and masks also work as expected -- eg. I used Levels on alpha channel of text layers in images below, to get a likeable indexized result.
Basically you can use any tool as you would on an RGB image; the 'pushing through' is really an effect that comes about due to the fact that you're painting in RGB but the displayed surface is quantized to the given palette, so the change only shows up when the "real color" is different enough to be quantized differently
Some indexpainted demos of Force vs Opacity (using standard brush tool w/ white fuzzy brush); hopefully this illustrates that Force works similarly to [Flow in Photoshop]
(Force)
(Opacity)
If this is not an adequate explanation, I was thinking about doing a video. Let me know if you'd be interested.
EDIT: actual sketch content: Quick test of Mypaint's new snowflake symmetry:
