Using LAB Color

Harold Davis
August 29, 2006
Landscape / Photography / Photoshop Techniques
17 Comments

Rio Grande near Taos, New Mexico, photo by Harold Davis. View this photograph larger.

I’ve been reading Dan Margulis’s masterful Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace. I thought I’d give some of the techniques he explains a try, starting with this image. I’m admittedly a piker with LAB color, but after this experience I’ll be using it more, and learning more about it.

You select LAB color on the Photoshop Image>Mode menu as an alternative to RGB (for computer monitors) or CMYK (for printing). You can’t really output anything in LAB, so a final step in any workflow in which you’ve converted to LAB is likely to be a conversion back to RGB or CMYK (depending on what you plan to do with the image).

The LAB color model consists of three channels. The L channel stands for luminance. Actually, this channel controls the contrast in the image, and appears in Photoshop as black and white. There’s some additional technical complexity in the way the A and B channels work, but essentially A controls the magenta to green spectrum and B controls the yellow to blue spectrum (both channels using a mechanism called the “opponent-color scheme”).

LAB color was originally specified by a standards body, the International Commission on Illumination (CIE). As the Wikipedia puts it, the LAB color model “is the most complete color model used conventionally to describe all the colors visible to the human eye.”

With the photo above, I converted to LAB color pretty early in my workflow. I was able to use the Curves dialog in Photoshop to easily color correct both the canyon area and the sky. By way of comparison, and to show what an excellent correction this is, here’s a link to a similar image from the same set that I processed a while ago without using LAB.