White balance is an adjustment to correct and neutralise colors captured with different light sources. The color of light can vary considerably depending on the time of day and whether you’re shooting in natural light or under artificial light. Our eyes and brains constantly adapt, but the camera records color exactly as it is, which can lead to unexpected color casts and shifts in pictures.
Digital cameras can correct these different colors using white balance. Initially, the camera records the full range of colors in the scene, then ‘corrects’ the colors according to the white balance setting you’ve chosen on the camera. The name comes from balancing the color rendition to mimic the effect of neutral ‘white’ light.
Auto white balance
Many photographers just leave the camera to work this out using its auto white balance setting. It will analyse the scene and correct it if it thinks there is an overall color cast. This can work well, but it can also cause some issues.
First, it may come up with a different color rendition for pictures taken at the same location at the same time, simply because the lighting is different.
Second, it may end up ’neutralising’ light that’s an integral part of the picture, such as the cold blue light of an early dawn, or the warm glow of the ‘golden hour’ in landscape photography.
White balance presets
This is why cameras also have white balance presets which lock the color rendition down to a specific setting, such as ‘Daylight’, ‘Cloudy’, or ‘Tungsten’. This makes the camera’s color rendition predictable and consistent.
On some cameras it’s also possible to set the white balance manually using color temperature and tint values. Color temperature is a concept that goes back to the days of film. It’s measured in degrees Kelvin (K). Warmer light has a lower color temperature, typically 4000K or lower, neutral daylight is around 5200-5500K, and ‘cold’ light has a higher color temperature of 7500-9000K and higher.
Digital cameras offer a more sophisticated system which adds a tint value across a green-magenta spectrum. Auto white balance settings, white balance presets and manual white balance adjustments on digital cameras use both color temperature and tint.
Custom white balance
It’s also possible to set a custom white balance value using a neutral white surface or a specially calibrated grey card. The camera measures the light from this surface, calculates a correction to make it appear completely neutral and this becomes a new custom white balance setting alongside the built in white balance presets.
If you shoot RAW files rather than JPEGs, you can choose the white balance setting later when you process the image on a computer. You can still choose the white balance setting on the camera, and this will still be the default value for processing, but because the RAW file contains all the color data captured at the time, you can override this with any white balance setting you like.
With RAW files it’s also possible to use a white balance eyedropper to click on any neutral tone in the picture to instantly ‘correct’ the white balance just as if you’d created a custom white balance setting with a grey card.