I apologize if this is a simple question, but I don't know the names of a lot of things yet so it's hard to do searches. I know how to find the intersection of two shapes in Photoshop. That feels like what I want, except I have two png. I want to find the overlap of the non-transparent pixels in them, as both have transparent pixels. Is there a best or easy way to accomplish this?
In Photoshop make a single document with the content of the two PNGs on separate layers. Merge the two layers Choose Select-->Load Selection Select the merged layer Choose Select-->Save Selection
You now look in the Channels palette where you now have a 4th channel of the combined layers transparency information.