The camera's built-in light meter sets the auto white balance based on a neutral gray, called 18% gray. This is the shade of gray half way between pure white and pure black. Using AWB, your camera's meter will decide upon some part of your scene that is more-or-less white and set it as 18% gray. Sometimes it is very obvious in the final photograph that AWB was used. For many landscape photos you might not notice it, but if you photograph a subject in a white sandy or snowy scene, your "white" sand or snow will become gray! The photo of the peppers below was taken on auto white balance. The peppers were sitting on a curved white cardboard. But the card looks gray in the finished photo because of the camera's meter and the AWB software. In this still-life photo, it might be considered part of my vision for the photograph, but in practice it was because I was too lazy to set a custom white balance.
Fortunately, setting a custom white balance is easy. Before photographing your subject, but in the same light, photograph an 18% gray card such that it fills the frame of your camera. It does not need to be in focus. Follow the instructions in your camera's manual to use this image to set a custom white balance.
18% gray cards are available from Adorama, B&H Photo, and other camera suppliers. The cards are inexpensive and easily stashed in your camera bag for use in location shooting.
What if you forget to set the white balance? If you save your images in RAW format, you can adjust the white balance during post processing. Both Canon and Nikon provide free software that lets you do this.
It is important for you to set the white balance in order to achieve the best quality photographs. Otherwise there will sometimes be an odd color cast in your images.
Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
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