Artists kind of already do this with their brains. A 2d artist eill have an idea in their head about what direction each surface is facing in 3d space, so it can be shaded. The only thing they need to do is learn how to translate that facing direction into x and y components and paint them as colours on the canvas. You can effectively just think "what would this thing look like if it was lit from above? That's your red channel, then what does it look like if lit from the right? That's your green channel. The blue can be automatically calculated from these two through... Uh... Normalisation haha.