I hope you are doing fine, I am testing Some Color Channels adjustment techniques for example like the following Video
https://www.youtube.com/watch?v=agH3mOPbGhshttps://www.youtube.com/watch?v=agH3mOPbGhs
Or
https://www.youtube.com/watch?v=dB0nBYN05CA
So which Tools we can use to do same job?
For basic calculations (multiplication, addition etc.) you can use the Blender node.
Other useful nodes:
Clamper (limits the minimum and maximum values)
Adjuster (adjusts contrast and brightness)
Inverter
Levels (stretches out values in the selected interval)
All the calculations listed work on RGB pictures or on individual channels (monochrome picture) as well.