How Ankulua works with transparency?

Ankulua ignores alpha. It converts RGBA to RGB (grayscale). (Transparent will converted to black)
You have to strip your pattern (with Paint.net or something else), so that it have nearly no unnecessary pixels.

A lot of developers do this in there scripts (including me) and we can use similarity from 0.7 (this is good enough for nearly everything) to 0.85.