Using the LAB color space

June 27th, 2007 by exhuma.twn

The LAB color space offers some very powerful ways to manipulate the coloring of a photo. With a little bit of imagination, one can achieve very interesting results even. I am currently working on some examples but it’s not all finished yet.

The examples are done in The Gimp! It should also be possible to adapt those examples to Adobe Photoshop as it also supports the LAB colorspace. Details may vary though.

A boring example of brightening up an image will follow soon.

To get you started:

0 <= L <= 100
-128 <= A <= 128
-128 <= B <= 128

L denotes the lightness such that 0 is black and 100 is white.
A separates magenta/red and green such that -128 is green, 0 is neither red nor green and 128 is red.
B separates cyan/blue and yellow such that -128 is cyan, 0 is neither cyan nor yellow, and 128 is yellow

A fun fact: With LAB you can specify impossible colors. Let’s say, you can crank up B to the maximum positive value, to obtain yellow. What happens if you reduce the L-value? Well it becomes “dark-yellow” which does not exist. Dark-Yellow looks brown to the human eye. Yet you can specify it. The same way you can specify “bright-green”.

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