Someone I know drew this cute frontal portrait:
They didn’t know how to shade it, so they asked me to do so. I used Procreate for iPad and a stylus. A half hour later:
This got me thinking about graphics algorithms! (I loved my college course in graphics algorithms, back in the day. We used OpenGL and C++ to do some pretty neat stuff. The projects were challenging but rewarding.)
I’m thinking that it shouldn’t be too difficult to write an algorithm that takes an unshaded frontal portrait and uses some heuristics about relative angles and lengths to transform it into a believable three-dimensional face. Then, it can generate a light source from a prespecified location and “shade” the face automatically. I don’t know if this has been done, but it seems fairly straightforward, so it probably has!