Lab Color Model


Today’s Question: Do you ever use the Lab color model?

Tim’s Quick Answer: I don’t typically convert images into the Lab color model, but that is actually the color model that is used in the background in terms of a color-managed workflow. That said, the Lab color model can be useful for a variety of tasks related to optimizing an image.

More Detail: I’m sure most photographers are familiar with the RGB color model, where colors are described based on how much red, green, and blue light is added together to produce a given color. Another common color model is CMYK, which describes the amount of cyan, magenta, yellow, and black ink must be combined to produce a given color in a print.

In the Lab color model there are three channels. The “L” channel specifies the luminance or brightness value for a given color. The “a” channel describes the color on a red/green axis, and the “b” channel describes the color on a blue/yellow axis.

The Lab color model is unique in that it is a device-independent color model. In other words, you can think of the color values as being absolute in terms of describing a specific color. By contrast, RGB values depend upon a specific profile, such as one that describes the unique behavior of a given monitor display. In other words, the actual color that results from combining specific values for red, green, and blue will vary based on the device and profile being used.

This is the reason the Lab color model is often at the center of a color-managed workflow. In effect, the color values in the image are interpreted to the Lab color model, and then converted again to color values to send to the printer based on a profile for the specific printer, ink, and paper combination being used.

You can also convert an image to the Lab color model with software such as Photoshop. One of the advantages of doing so is that the tonal information is separated from the color information. So, for example, you could focus your sharpening on the L (luminance) channel to ensure that sharpening doesn’t alter the colors in an image.
Some photographers also prefer to use Lab for color correction, since the two color channels are separate from the luminance channel. And you can apply various creative effects using special techniques with the Lab color model.

For my purposes the Lab color model doesn’t provide a benefit that would cause me to convert an image to Lab. However, as noted above, I absolutely benefit from the Lab color model in my photography, since Lab is the foundation of a color-managed workflow.