To see this LAB fix at work pick an image that has color in it but which you think could use a color boost.
Step 1
With the flattened image open in Photoshop, choose Image > Mode > LAB Color. If you’re working on a flattened image you won’t see anything except LAB/8 appearing in the title bar of the image.
Step 2
Duplicate the background layer of the image by right clicking it and choose Duplicate Layer. You’ll make your adjustments on this duplicate of the background layer so that you can blend them into the background layer later on.
Step 3
Choose Image > Adjustments > Curves to apply the curves adjustment to the duplicate background layer. Don’t use an adjustment layer as you’ll only have to flatten it on returning to RGB anyway.
In the curves dialog, the L channel is visible on the screen. This channel that contains only lightness and darkness values so that you can drag on the curve to adjust this if desired.
Step 4
Select the a channel … this is the magenta/green channel. In a standard Photoshop setup green is on the left and magenta is on the right. Drag the bottom edge of the curve inwards 2-3 squares. Then drag the top edge of the curve inwards the same number of squares. It doesn’t matter how many squares you drag but you must drag the same number on either end so the curve line crosses the middle of the grid … this stops you from inadvertently inducing a color cast into the image.
Step 5
When you’ve adjusted the a curve, repeat the process with the b curve. At this point the image is probably looking very scary indeed. However, you need to make the adjustment strong enough that you get too much color rather than too little at this stage. Click Ok to apply the curve to the top image layer.
Step 6
To return to RGB mode choose Image > Mode > RGB Color. When prompted, select the Don’t Flatten option. This is critical because you want both layers intact back in RGB mode.
Step 7
Now drag the Opacity slider for the top layer back to 0 so you see the original image and slowly walk the slider back up until you get the amount of color you want in your image. When you’re done, save the result.
Once you’ve done this a couple of times, you’ll appreciate how much of a boost in color you can get and how fast you can do it. Record the fix as an action and you can do it in one click and then just adjust the opacity to suit.
In some cases altering the blend mode of the top layer can yield pleasing results. The blend modes in the Overlay, Soft Light, Hard Light, Vivid Light, Linear Light and Pin Light grouping in the Blend Mode list give the best results. You can also duplicate the top layer and apply different blend modes to each copy to bring out different areas of the image.
So, if you want to produce eye-wateringly beautiful color in your photos, chances are that a Lab color fix like this is just what you need.
The images below show the original image on the left and the LAB color fix applied to it in the image on the right. No adjustments other than working LAB and blending the resulting layers
have been used on the right hand versions.
Post Script: To learn more about LAB color mode and the fixes that you can perform using it, look no further than Dan Margulis’ book Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace … it’s practically the definitive book on Lab by the master of Lab himself.