How to handle alpha in a manual “Overlay” blend operation?

Question

I\'m playing with some manual (walk-the-pixels) image processing, and I\'m recreating the standard \"overlay\" blend. I\'m looking at the \"Photoshop math\" macros here:

Answer 1

I was experimenting with this issue exactly, until I found out that the best is to have the base and the blend layer both with straight alpha, then premultiply only the result with the base alpha.