Understanding Lab anatomy

The Lab mode features three color channels, one for luminosity and two others for color ranges, known simply by the initials a and b. (The Greeks would have called them alpha and beta, if that's any help.) Upon hearing luminosity, you might think, "Ah, just like HSL." Well, to make things confusing, Lab's luminosity is like HSB's brightness. White indicates full-intensity color.

Meanwhile, the a channel contains colors ranging from deep green (low-brightness values) to gray (medium-brightness values) to vivid pink (high-brightness values). The b channel ranges from bright blue (low-brightness values) to gray to burnt yellow (high-brightness values). As in the RGB model, these colors mix together to produce lighter colors. Only the brightness values in the luminosity channel darken the colors. So you can think of Lab as a two-channel RGB with brightness thrown on top.

To get a glimpse of how it works, try the following simple experiment.

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