On: Image Processing 101

[GFK_of_xmaspast]

> I'd assume that you select a color and

This is not at all how edge detection works. See https://en.wikipedia.org/wiki/Sobel_operator for a key building block.

[EvanPlaice → GFK_of_xmaspast]

Thanks!

I wasn't aware of this approach. Looks like a reasonable single-pass solution.