Compositing Node Background

Hey guys.
Just a week learning Blender.
I’m creating video by this tutorial i guess he is using older Blender version and not telling how to add background.

question is - why it’s not showing or how to apply background?
Attaching blend file and screenshot.



sniper.back.blend (550 KB)

He explains it just where you’ve linked

The tutorial uses the values on the rendered image itself to mix the two. Yours is grey, with actual values of 0.04 - 0.08, so it only mixes 4-8% of the image in.

Tutorial renders with a black background (value 0) and white objects (value 1), so the render itself works as a mask.

An alternative is to use transparent background in the render (film: transparent) and use the alpha as a mix factor. Alpha channel is also a greyscale mask, just like every color channel, the alpha channel looks like the rendered image in the second with black background and white foreground.

ctrl+shift+lmb click on a node to connect viewer to it. Alt+lmb on the backdrop shows the values, but I like to disable the backdrop and open the viewer in the UV/image editor instead to keep the nodes clear. Holding down lmb shows the values in the image editor, and in this the background has linear value of 0.05, which is 5% when used as mixing factor.