[Closed] Copy bitmap alpha

Hi everyone! My goal was simple: take 1 bitmap, take another, and copy alpha channel b1.a = b2.r

Plenty of solutions: setPixel, pastBitmap e.t.c
But nothing is working ;_; I’ve spent whole day googling. Maybe there is a catch somewhere?

This is how I get bitmaps from substance:

sbsMat.DiffuseMap.outputChannelIndex = 2	
_filename1_ = "C:\	1.png"	
meditMaterials[1] = copy sbsMat
rm = renderMap meditMaterials[1].diffuseMap size:[_width,_height] \
fileName: (_filename1_)

Same for 2nd bitmap.
If I save them to file, I get 2 good looking pngs. One with color. Other black-white mask as it should. And no extra alpha channels ;_;

I did this prior too:

     	pngio.setType #true24
     	pngio.setAlpha true		

Maybe renderMap function is bugged or it returns bitmap without alpha channel and I have to add it manually somrhow?