LAB is one of the most prominent ways of many to define color. The L stands for Luminosity or Lightness, and the A and the B don’t actually stand for anything, but refer to the ‘green-red axis’ and ‘blue-yellow axis’ respectively. Accurately describing color on a whole is very difficult; an easy example to describe this is the color red. Everyone knows via RGB definition that red is universally referred to as 255,0,0.
However, for you to know the exact color someone is describing, you would need to look at what Photoshop Color Settings they have, due to the number of different definitions there are for RGB. This is where LAB Color comes in, as there is only one Photoshop LAB setting.
1. The first step is to find and image. I’ve selected this image because it has some details to demonstrate the LAB correction in action. However, you can also follow this tutorial with your own images. This photo is contributed by Philipcs.
2. Its always a good practice to make a copy of the original image so that you can compare the end result after going through the tutorial. Keep both versions open so that you can switch between the two easily and quickly.
3. Now, you need to switch to the LAB Color mode. To do this, go to Image > Mode > Lab Color, which will automatically convert the image. The picture will look no different at first, but the identification bar at the top of your image will display ‘Lab’.
4. In this tutorial, we are concentrating on the curves and channels. Bring up the Curves dialog box by clicking Image > Adjustments > Curves. Click on the arrow in the middle of the lightness to darkness gradient. Make sure the lightness is on the left hand side.
The next thing to customize is the percentage intervals of the grid lines. The default is set to 25 per cent increments. This will cause changes to be a little too coarse for our image, so Alt-click on the grid and toggle the lines to 10 percent intervals instead.
5. Click the word Lightness and select ‘a’. Click on the top anchor and move it until it has the value of Input 85 and Output 100. Click on the bottom anchor and move it until it has the value of Input 15 and Output 0.
6. Select the ‘a’ and change it to the ‘b’ menu item in the Channel drop-down list. Repeat exactly the same process as you did for ‘a’. Set the top anchor to Input 85, Output 100 and the bottom anchor point to Input 15, Output 0.
7. Now got back to the Channel drop-down menu and select ‘Lightness’. Drag your mouse around your image and see the circle move in the Curves dialog box. To make the tonal range steeper, simply click on the middle point of the diagonal line to create a new anchor point and drag it across the grid. The value of this point should be Input 55 and Output 60. Click OK to commit the changes.
8. Select Windows > Channels to bring up the Channels palette. Select Lightness to show the Greyscale Lightness image. Go to Filter > Sharpen > Unsharp Mask. The filter dialog box will appear. Set the following values: Amount - 200%, Radius - 1pixel and Threshold - 10 levels and click OK.
9. Now reselect the LAB layer from the Channels pallete to display every Channel again and a full color image. We’re done adjusting the image in this mode and it is time to convert the image for use in projects or sending to clients. I’m now saving it for web, hence I’m converting it back to RGB mode.
Compare it against the original image that you have made a copy earlier on. Now you should be able to see that the image has become more vibrant and sharper.
When should you use LAB?
LAB Color is a mode that should only be used as an intermediate color model before switching it back to either RGB or CMYK. You can save out documents with LAB Color mode still applied, but only a very few number of advanced image manipulation software packages, including Photoshop will be able to read it.
LAB correction can sharpen and boost colour in a digital image, but works best o n certain types of digital images with specific characteristics. First the images should not hav any large areas of brilliant colour or images that have highly saturated colours.
Also, LAB Color will not correct, nor be effective on, images that have been tinted with a noticable color cast. Finally to get the best result for LAB Color correction, the digital image that you are working should not have had an Unsharp Mask filter previously applied.
