Use a Gray Card to Make Accurate Color Corrections in Photoshop

Adapted from Digital Photography: Expert Techniques (O'Reilly)
By Ken Milburn

Dateline: April 25, 2005
Version: Photoshop CS

More Digital Photography tips
Discuss this in the Digital Photography forum

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.

  1. When you get the image with the gray card/cloth into Photoshop or Photoshop Elements, open either the Levels or Curves dialog. (The Curves dialog is shown in the next illustration.) At the lower-right side of the dialog, you will see three eyedroppers: black (shadow), gray (midtone), and white (highlight). Choose the gray eyedropper, click on the gray card in the photo, and presto! The color balance in that image is instantly perfect, yet your overall exposure doesn’t change.

    The Curves dialog with the gray Eyedropper tool highlighted.

  2. In the dialog, click the Save button. This will save the settings used to correct the image. When the Save dialog appears, give the .acv file a category name that describes all the images you want to correct according to the same setting. Save and close the gray card file.
  3. Drag all the other files you want to color-correct into the workspace so that they’re all open at the same time. Click each in turn to make it active, then press Cmd/Ctrl-M to open the Curves dialog. Click the Load button (it brings up a standard File Open-type dialog) to load the .acv file you saved for the gray card exposure. When the file loads, the color balance will automatically correct. If this is the last curves adjustment you need to make for this image, just click OK and then Save As, and add "clr corr" to the filename just before the final serial number.
  4. Repeat the third step for all the other images in the series. The gray-card routine works even faster if you create a Photoshop action for it. All you have to do is create a new action. Name the action in the resulting dialog and click OK to start recording. Then perform these steps and click the Stop icon at the bottom of the Actions palette when you’ve completed the routine.

    Sadly, it’s not practical to stick a gray card into every shooting situation. All too often, you simply need to shoot first and ask questions later. Thankfully, Photoshop lets you correct color balance in numerous ways, so with a little bit of effort you’ll likely produce a perfectly acceptable result. For instance, you can color-correct specific areas of brightness by using the Curves dialog on one or more color channels; and you can even break down and use the Image > Color Balance, Image > Hue/Saturation, or Image > Variations dialog to change the color balance. If you’ve shot RAW files, you can also make adjustments with the Temperature and Tint sliders in the Adobe Photoshop Camera RAW plug-in dialog.

    If you use the Levels or Curves command as an adjustment layer, you can instantly adjust other images shot in the same conditions. To do this, open the original image and its Layers palette and link all the adjustment layers. Next, open any image in which you want to make identical adjustments. Make the first image active and then drag the linked adjustment layers to the image you just opened. The original adjustment layers instantly appear in the Layers palette of the new image, and the layers are automatically adjusted.

    Discuss this article in the Digital Photography forum. Make sure you don't miss the next Digital Photography article. Get the free newsletter in your mailbox each week. Click here to subscribe.

    This article is adapted from Digital Photography: Expert Techniques (O'Reilly) by Ken Milburn and is reproduced here with permission. Copyright 2004, O'Reilly.