And since this toon shader relies on a color ramp, is there a way to input the image as one of the colors? If no, then is there another way to recreate that shading effect but keep the texture?
You can do that too, but then you have no soft gradient between the different colors since the greater than node only outputs 0 or 1. But if you dont need a soft gradient, this(“greater than”) is also a way to do it.
One restriction is to keep the stops in order (lowest to highest) if not it does not work like the normal colour ramp.
PS
With these node groups you can animate the textures, the position inputs etc.
Also you can use gradients or textures for the position inputs. They are fun to play with.
Color ramp with inputs is pretty cool and amazing, but I think this is an XY problem to begin with. Or at least I would have no idea how to combine the images shown into something that would use cell shading and those textures. Might the idea be to simply use a texture, but then cell shade it?