For clarity if anyone is still confused, on Wikipedia's example image, look at the snakes's shadow - that's what's happening to the background in the blog's ima

For clarity if anyone is still confused, on Wikipedia's example image, look at the snakes's shadow - that's what's happening to the background in the blog's image. I didn't know the word "posterization", so I'd describe this (slightly?) more simply as a stepped gradient instead of a smooth gradient.