I'm sure there's a dead simple solution to this problem. I've been trying to build a simple composite node for a PB Graph that takes three inputs, maintains transparent areas in the "top-most" layer (Layer 1), 50% opacity overall for the middle layer (Layer 2) and 100% opacity for the bottom layer (Layer 3) without applying mathematical blending (like multiply or linear dodge blend modes).
If someone could point me in the right direction with regards to "Normal" blend mode (as in Photoshop), I would be much obliged...
Thanks in advance!
The PDF Reference Manual gives the formulas for many of Adobe's blendmodes so start there:
Of course it never hurts to go back to Porter-Duff: