Last night I tried processing an image in Lab color space for the first time. If you’re not familiar with Lab, it is the most accurate color space and has a gamut that covers the entire human visual spectrum. There’s an interesting article written by Jeremy McCleary that describes how human vision works and compares it to the Lab color space which is as close of a match as you can come – Human Vision and Digital Imaging.
Basically, Lab separates luminance (think black and white) from color. Similar to RGB, there are three channels. However, with RGB the channels are Red, Green and Blue. With Lab the channels are L for luminance (brightness and darkness), a for magenta green opposition and b for yellow blue opposition.
The advantage of Lab over RBG (or CMYK) is that the luminance can be adjusted without affecting color and vise versa. In RGB changing luminance will affect color saturation; in Lab it doesn’t.