combining render with alpha

Support Compositing and Post Processing
1

Hello,

I have rendered out an image in Blender, and rendered out the greyscale alpha channel image seperately. Is there any way I can recombine the two images in the node compositor, using the greyscale alpha image as the first images alpha channel? I need to overlay the image on top of another image. Any help would be appreciated.

2

Put the 2 images through a mix node with the alpha image plugged into the fac. input.

This will mix the 2 images together according to the greyscale value of the alpha image.