When it comes to color spaces, you already work in RGB, you may have heard about CMYK, but there is another color space that is lesser-known yet highly useful. It’s called “Lab,” and it isn’t something cooked up in a laboratory or carried in by a Labrador retriever.
Like RGB and CMYK, each letter represents a channel. The “L” stands for “lightness” and is where luminosity data lives in the Lab color space. The information contained in this channel is greyscale and represents tonal values without hues. The hues reside on the two remaining channels, “a” and “b.” Colors on the red to green spectrum are represented on the “a” channel, and the “b” channel holds data for the blue to yellow spectrum.
With the understanding of how the Lab color space works, you are equipped to easily match colors with precision in Photoshop using the Info panel, eyedropper tool, and a Curves adjustment.
How To Match Colors In Lab Mode
First, open the image that you’d like to alter colors in Photoshop. In the video attached, Colin Smith of photoshopCAFE demonstrates the technique by changing the color of a woman’s shirt. Into the same document, open an image that contains the color you want to apply to your image.
To source the color he will make the shirt, Colin has chosen a blue parrot fish. He recommends looking to nature for color theory inspiration, and noticed that the fish had a yellow on its tail very similar to the hat worn by his subject, and so thought it would be a good match.
Using Photoshop’s menu, navigate to Image > Mode > Lab Color to change your document’s color space to Lab. You will be asked if you’d like to flatten the image; opt to leave layers intact. The image will look the same, but navigating to the channel’s tab will reveal the difference under Photoshop’s skin. Instead of red, green, and blue channels, you will see Lightness, a, and b channels.
Now, access the Info panel via Window > Info. This will bring up a panel that shows numerical values for each channel as you hover your cursor over different parts of the image. Grabbing the Color Sample eyedropper tool, you can add sample points to your Info panel that will capture the exact values of targeted areas.z
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Use the Color Sample eyedropper to sample both the source and destination colors, making sure that the sample size in the tool menu at the top of the screen is set to at least 11 x 11 average.
Once you’ve got your samples, make a selection of the are you are going to change.
In Colin’s tutorial, he uses Select > Color Range and then uses other tools to refine the selection. Then, make a curves adjustment layer. In the Curves panel, click the little hand with an extended finger between two arrows to sample the image for an exact place on the curve, and holding Control/Command and Shift key to apply the selection to all three channels, click where you sampled your color to change.
From here, changing the color is as simple as looking at the values of the source and destination samples in your Info panel and changing the value in the “output” box beneath the curves graph from the values seen in the sample of the original image to the values sampled in the image which you are using to source your color.
Do this on all three channels, tweak your curve to even out the colors, flatten your curve onto your background so you don’t lose it when you convert back to RGB, and you’ve got an exact color match!
This is probably a bit much to take in all at once via text, so watch Colin’s video below and refer back to this article as you do your own color matching.