In this context, an image where there's some data represented by each unique RGBA value, and less of the "smooth" complexities of normal images like from a camera. So ones with small color palettes. Depending on the output size, it can run very fast and I've used it to up-scale a simple 2-color map for an island in water off one 512x512 training image.

I tried to demo this to HN back in July, but my post back then was buried.