monochrome

You have a consoleized Virtual Boy and I'd like to show it off in 3d. What are the seemingly easiest ways for this to make a red and cyan anaglyph. Step 1 I could do easily. Get pictures of two eyes and turn the color saturation to negative 100% to get a monochrome black and white picture...

Also for Virtual Boy I would like to make those pictures monochrome and merge them with red and cyan. I can turn a color picture into a black and white picture by using Color saturation at negative 100%. But there's two other things I can't easily do that if there were commands should be...