LAB Color and Tonal Adjustments in Photoshop

A color space, or color model, is a structure for referencing and notating color values. As you likely know, the RGB color space is a color space with three channels—Red, Green, and Blue—commonly used in LCDs and monitors. CMYK is a four-channel color space—the color channels are Cyan, Magenta, Yellow, and Black—used to describe the color values in images that will be printed in books and magazines.

LAB is a three-channel color model—I’ll explain how the channels work in a moment. Unlike RGB and CMYK, LAB is a theoretical model in the sense that you can’t save a LAB image as a JPEG for display on the web, and there are no reproduction processes that use LAB to print things. But LAB has a couple of features that make it excellent for manipulating colors. Once you get the hang of it, it is easy to use LAB colors to make your landscapes go from drab to fab!

As the sun set to the west of Stinson Beach, California, I marveled at the glory of the colors reflected in the nearly still waters of the Pacific Ocean. But when I looked at the capture on my computer, it seemed dull and lifeless (check out the initial version of the photo, above). To recreate the vibrant colors as they seemed to me in the time and place I shot the photo, I first multi-RAW processed the image and then used LAB color adjustments. 18mm, 1/50 of a second at f/9 and ISO 100, tripod mounted

In Photoshop, to work in LAB you have to convert your image into the LAB color space. Once you are finished working in LAB, if you want to actually do anything with your photo, you need to convert it back to RGB or CMYK.

The two features that make LAB particularly powerful for working with color are that it separates grayscale information completely from color information, and that each of the color channels are color opponent, meaning they include information both about a color and its opposite color. The ways these features work in Photoshop are shown in the figure below.

You have to work with LAB for a while to understand just how much these facets of LAB can be used to improve your landscape photos; a good example is the next case in which I’ll show you how to use these LAB features to make the colors of a rainbow bolder and brighter.

LAB Color and Tonal Adjustments

I’ve told you that LAB is fabulous for working on color, now let’s take a look at how you can use it practically.

The diffuse mist under Yosemite Falls (shown below) lent itself to a rainbow when the sun peeked through the clouds. But looking at the image on my computer, I was surprised by how dull the colors were. This would not do!

Converting to LAB color 
There are two ways to convert to LAB color in Photoshop. You can select Image > Mode > LAB Color. Or you can choose Edit > Convert to Profile, select Lab Color from the Destination Space drop-down list, and then click OK.

To convert an image back from LAB color, use one of two methods: select Image > Mode > RGB or CMYK; or choose Edit > Convert to Profile, then select RGB or CMYK from the Destination Space drop-down list, and then click OK.

At the bottom of Yosemite Falls, the mist creates a lovely rainbow. I was able to capture this lovely prismatic effect, but at home on my computer, the colors did not shine as brightly as they had in the field. So, instead of accepting the “As Shot” defaults, you can get a little bounce in color and saturation by pushing the Saturation and Vibrance sliders to the right in ACR, and also by slightly raising the color Temperature (see the settings above in the ACR dialog).

However, even following multi-RAW processing this image doesn’t begin to have the kind of sparkle and color that I’d like to see. The answer: selective painting with LAB color adjustments to enhance the colors of the rainbow. By the way, selective painting with LAB has one big advantage over simply painting in colors: the LAB adjustments already have the underlying shape of the elements of the photo, so you don’t have to worry much about precision when you apply the color.

With LAB color I can quickly create “color palettes” that I can use to paint in the shades of the rainbow. To make this green and magenta version, I converted the rainbow photo to LAB color. Then I duplicated the image by selecting Image > Duplicate. After selecting the A channel in the Channels palette, I applied an Equalization adjustment by selecting Image > Adjustments > Equalize. This maximizes the greens and magentas in the duplicate image.

To make this blue and yellow version, I again duplicated the original image by selecting Image > Duplicate. I made sure the B channel in the Channels palette was selected, and then I applied an Equalization adjustment to that channel by selecting Image > Adjustments > Equalize. This maximizes the blues and yellows in the second duplicate image.

Then I selected all the channels in the Channels palette and applied an Equalization adjustment by selecting Image > Adjustments > Equalize.

Increasing Contrast with LAB 
The equalization above looks pretty odd, but it can be used to attractively expand the grayscale tonal range of the image. To do so, drag the image onto the original image. Then using the Layers palette, set the layer’s Blending mode to Overlay or Soft Light, and lower the opacity of the new layer to 10–20%.

After dragging the two equalized “color palettes” (the green/magenta and blue/yellow images above), I added a black Hide All layer mask to each layer, and then painted in the rainbow’s colors using the Brush Tool with white selected as the Foreground Color.

This final version is much closer to the vibrant colors that I saw when I captured the rainbow at Yosemite Falls.