Further to yesterday's post about Channel Mixer, here's another example of its use. This time, it saved me from a heck of a lot of tedious cloning!
This is a section of an old family portrait that I have been commissioned to restore. You can see that there is a lot of yellow mould, or mildew, or something:
Seeing that made me want to run a mile! But I cheered up once I examined the individual channels.
Red channel - pretty awful:
Green channel - slightly better, but still awful:
Blue channel - miraculously almost free of dots:
This is because blue is yellow's opposing colour, so it is least affected by yellow problems.
So, I began the restoration job with a Channel Mixer layer, to use the blue channel only. Obviously, there are still some dots and stuff, and it's kinda dark and flat, but it's by far the best option.
With some careful work (nearly four hours for the whole photo) I've got it to here: