White balance, or WB, is necessary on cameras as light doesn’t just vary in brightness, but also in color. Each light source has its own individual ‘color temperature’, which varies from red to blue as you move through the visible spectrum. Human vision is very good at compensating for this, so a sheet of white paper will look white whether it’s viewed in daylight or by candlelight. It’s the job of the camera’s White Balance system to do the same thing and compensate for the color differences in the lighting, so the colors in a scene look exactly as we would expect.
Digital cameras have a wide range of options for controlling the White Balance to suit the color temperature of the light in the scene, including Automatic White Balance (AWB), which will cleverly look after all this for you. However, as with all your camera’s automatic settings, the Auto White Balance isn’t foolproof, and it may under-compensate for extreme conditions because it can only operate within a restricted range of temperatures.
The Kelvin scale
Color temperature is measured on the Kelvin (K) scale, and a camera's automatic AWB system can only usually adjust between 3500K and 8000K. It will struggle to get a picture that doesn’t look orange when you’re shooting in your front room at night, for example, as the color temperature of domestic lighting will be lower. It may also struggle just before dawn, when the light is blue-toned and has a higher color temperature than the Auto setting can cope with.
Your DSLR or mirrorless camera, therefore, has a number of manual White Balance options that enable you to take full control. The easiest to use are the white balance presets. These are settings designed specifically for different light sources, such as flash, incandescent light (domestic light bulbs), sunny days, cloudy days or deep shade. They are useful for getting consistent colors within a sequence of pictures, or for tricking the camera into giving you slightly warmer- or colder-looking results.
For more control over color temperature settings, you need to use another manual option. Although not found on all models, the K setting enables you to set a specific color temperature. This is great for precise control because you can dial in any setting from, say, 2500 to 10,000K.
Of greater use, and available widely on digital cameras, is the Custom White Balance setting. This is set by taking a measurement from a test target, such as a sheet of white paper. Just ensure this fills the frame and is in the same lighting you’ll be using for your photos.
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