Cameras capture subjects illuminated by a light source. The colour of that light, however, is neither static nor neutral. Look at a white car during daylight. Your brain tells you it’s white. Well and good. Now look at a white car under a streetlamp at night. It now looks yellow/orange. This is called a colour cast. Tungsten filament bulbs generate another orange cast, fluorescent lighting adds a green cast and flash lighting is usually blue.

The human brain can compensate (that car is white, we know), but cameras don’t. If you shoot with film, you have to buy specially treated rolls and add gels or filters. Digital cameras all feature another solution: Automatic White Balance, which basically decides what colour white is. In most cases, your camera gets it more or less right. When it doesn’t, image-editing software can help. How complicated the process is to correct the white balance depends on the software, but shooting in RAW is always a good idea when you’re unsure, because corrections can be made non-destructively.

Below is an example of colour cast. The image to the left is set on automatic and the subject is basically orange because the main light source has an orange colour cast. The corrected image is obviously on the right. The second light source, daylight, now looks a touch too blue on the right.


How to get it right and does it matter? In most cases, it doesn’t, but portraits do require colour accuracy, if only because very few people really do have a greenish or bluish tinge in their complexion. The best way is to buy a colour swatch or gray-scale card which retails for about $10. Place it beneath your subject in the first good shot where you’re sure of your lighting and refer to it afterwards when editing your images. (This is what the pros do.)

For general landscapes, macros, etc., you can usually rely on your camera’s AWB setting. However, if you use a Point-and-Shoot only in JPEG, you might want to experiment. The usual settings are Automatic (one sizes fits all), Daylight, Cloudy, Tungsten, Fluorescent, Flash and one called “custom” (there are sometimes others depending on the camera make). Before taking a shot, go through each one to see which looks best to you.

When should you think about doing this? When there are multiple and different light sources, such as in the image above.
How to adjust the custom setting varies from one camera to the next. The principle is basically the same and is rather like the “adjustment layer” function in Photoshop: point at something that is supposed to be white and adjust the setting until it actually is…

The rest of this explanation is copied from Charlotte K. Lowrie’s Digital Field guide to the Canon EOS 40D (Wiley, 2008):

“Color temperature is important to understand because different times of day and different light sources have different color temperatures, and to get accurate colour in images, the camera must be set to match the temperature of the light in the scene. Color temperature is measured on the Kelvin temperature scale and is expressed in degrees abbreviated simply as “K”. So for the camera to render color accurately, the White Balance setting must match the specific light in the scene. For example, sunlight on a clear day is considered to be between 5200 and 5500K, so the Daylight White Balance setting will render colors accurately in this light.

When learning about color temperatures, keep in mind this general principle: the higher the color temperature is, the bluer the light; the lower the color temperature is, the yellower/redder the light.”

The inimitable Ms Lowrie also helpfully provided a table of selected and artificial light colour temperatures, which I have added below. I hope this helps.