Use a Gray Card to Make Accurate Color Corrections in Photoshop
Adapted from Digital Photography: Expert Techniques (O'Reilly)
Dateline: April 25, 2005
If you are shooting in a shaded area next to an intensely
colored wall, shooting with mixed lighting, or using
fluorescent tubes that vary in color from their stated color
balance (a maddeningly common occurrence), you may
have a hard time adjusting color balance in Photoshop. This is because you have to guess at the proper changes in
more than one color channel.
One way to help is to start by taking a test shot that includes an 18% gray card (or other item that is 18% gray), as shown in the illustration below. These cards reflect 50% of the light cast on to them. Kodak’s 18% gray card is very popular and can be found at most pro camera stores. Microstar’s 18% gray lens cleaning cloth is compact, inexpensive, and serves multiple purposes. Personally, I like to order several cards at a time (they’re easy to lose) and it’s a good idea to have one in every camera’s carrying case so that you don’t forget it when you venture out to shoot.
The subject has a bluish cast. An 18% gray
lens-cleaning cloth has been placed in the frame.
If you place your camera in spot-meter mode and set the white balance to automatic, you increase your chances of getting the proper color balance in the image when you take the shot. Unfortunately, the camera will probably pick another color balance as soon as you move the gray card or cloth from the picture. The best way around this is to keep the shutter button half depressed to lock in the settings, have someone else remove the gray card, then press the button all the way to take the shot.
If you can’t do that, the gray card still serves a purpose, as it can be used by Photoshop as a basis to balance the overall color and exposure, yielding a photo such as the one below.
This image has been color-corrected with the same settings
used to correct the first one. The color corrections were made
in the Curves dialog, and the exposure corrections were made
at the same time.
Here’s how you do it.