Photoshop has this weird mode called Lab color.
No, Lab does not stand for laboratory.
Lab is a three component color system.
RGB had 3 colors, CYMK has 4 channels, but Lab’s channels are a little different.

RGB is an additive color space, adding red makes the image redder, green, greener blue, bluer. Your computer monitor fills your eyes with color with millions of individual color cells of red, green and blue.

CMYK is for the printing industry. It is subtractive. Cyan, magenta, yellow and black. Cyan removed red from an image, magenta removes green, yellow removes blue and black removes light across all spectra, allowing you to print dark colors by adding small amounts of black (referred to K for very esoteric reasons) instead of lots of CMY and soaking your paper.

These systems are interesting in that when you change the amount of R,G,B or C,M,Y, or K, you change the overall amount of intensity of the image.

Lab is different.

Lab stands for Lightness, “a” and “b” where a and b are convoluted ways of referring to color. There is math there, and if you are mathematically inclined, you can go down that rabbit hole. The neat thing here for me, in the context of this page on my blog, is that the L channel is an interesting place to play.

This is a very noisy image: by design.
The problem was that working with the image as you would any sort of image in photoshop was painful in RGB. Copying and pasting areas in RGB to correct for dirt on my sensor was very noticeable.

I don’t want to give away all my secrets, but these images started out as very washed out (an artifact of my zone plate) and needed a lot of processing to get them to a good level.

The “character” differences between the channels was enough to make a difference. Most noticeable is the size of the grains of noise .

Anyhow. This is an interesting tool. You can treat color differently than lightness. I also use this mode for dealing with color infrared images and just as a different place to play.