It’s probably as ancient trick as a famous silk road. I have background image which I am currently testing for my scene. In the first instance I have this node set up without Light Path node to make my background image transparent in which I use emission node to control background image brightness . It works :
In the second node set up I use Light Path (shadows ray) and my background comes out a little too washed out for my taste. So I try to crank the brightness by hooking up curves node but no matter what I do with curves it doesn’t effect background image in render:
What do I miss?