Interpreting a* and b* in L*a*b* color space

In L* a* b* color space, I know L* corresponds to “lightness” so that as L* increases I can say colors are lighter. Is there a similar term that corresponds to the color channels a* and b*? For example, as a* increases can I say that a color’s red shades are more intense or saturated? I want to make sure I use these terms correctly.

Answer

First, we need to understand what is the concept of the different Lab modes.

The premise is that one perceived color, as humans do, can not be at the same time its complementary color.

Let us use yellow as an example.

  • Yes, you can have a “redish” yellow
  • Yes you can have a “greenish” yellow
  • But you can not have a bluish yellow, because before it turns into blue it needs to pass thru green.

Yellow is the complementary color of blue.

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On the other color models you add a component, for example RGB you can have no red (0) or a lot of red (255)

But in Lab you have two “complementary” colors on the same scale. This means that the a and the b are not representing one color but an axis of complementary colors.

I am going to steal @Billy Kerr’s image

Colour Balance in LAB mode

Two colors that, if mixed in this model, the cancel each other and make a neutral gray.

So the scale is not 0 to 255 but -128 to +128 where the 0 is at the middle indicating that you have a gray.

If you go off this axis you simply move away from gray to yellow or blue.

increases can I say that a color’s red shades are more intense or saturated?

Close but not exactly.

  • Yes if you are further away from 0 you have more “saturation” on that direction.

  • No, because “Increase” can render a color less saturated, if you consider that you have negative values. -50 is a smaller number than -20. It increased but the color is less saturated. A “correct” term would be “further away from 0” in either direction.

Some Lab models do have Red as a component. (But in other models, the Magenta is used). I will use the Red as an example.

It is not shade, but a component. The difference is that if you say “Red shade”, you expect to see Red or Redish.

But if you also have a Blue component you will see Purples and wine shades, not exactly Red shades but Red compoent.

That is why they used a letter. It is an axis.

It could be called L-GR-BY or L-GM-BY. But it is a bit harder to say.

Attribution
Source : Link , Question Author : KAE , Answer Author : Rafael

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