I now carefully select and mask out each part of the image that will be a different texture or color, saving each mask with a descriptive name. Painter lets me choose the mask display color, so I set it to an approximation of the final color to let me judge the composition. This is the most painstaking and fiddly part of the process; it took over 3 hours for this pic. To save memory, I combine some small parts that are non-adjacent into the same mask.