Compositing na ARGB8888 image from four L8 images

[JeffC]

I was trying to compose an ARGB8888 image by overlaying four L8 images for the alpha/red/green/blue. I am not getting it right. Does anyone have a sample display list to achieve this task ?

In a second quest, I wanted to not provide the A channel, and instead use the RGB channels to create a one-bit alpha channel on the spot (wherever R, G or B is non-zero, alpha should be full on). I also didn't succeed here. Any help would be appreciated. The engine is still a bit mysterious to me even though I am trying to understand the math behind it ...

Thanks a lot !