What are the algorithms used behind filters in image editing softwares?

Question

For example: What algorithm is used to generate the image by the fresco filter in Adobe Photoshop?

Do you know some place where I can read about the algorithms implemented in these filters?

Answer 1

Lode's Computer Graphics Tutorial

Answer 2

The Photoshop algorithms can get very complex, and beyond simple blurring and sharpening, each one is a topic unto itself.

For the fresco filter, you might want to start with an SO question on how to cartoon-ify and image.

I'd love to read a collection of the more interesting algorithms, but I don't know of such a compilation.