What is white balance in a camera?

White balance in a camera adjusts the colours in a photo so that white objects appear neutral white under different lighting conditions. It compensates for the changes with light source so that the colours look more natural and accurate. Our eyes have a great capacity to see white as white, while it is not so for the camera under different lighting conditions. As an example, a photo taken under a warm, yellowish indoor light may appear to have a yellow tint while one taken outside on a cool, cloudy day may look bluish.

Here is an image from Wikipedia showing the variations with adjustment of white balance. These three are versions of the same image taken by the Mast Camera on NASA’s Mars rover Curiosity. The left image is the raw, unprocessed color, as it is received directly from Mars. The center rendering was produced after calibration of the image to show an estimate of “natural” color, or approximately what the colors would look like if we were to view the scene ourselves on Mars. The right image shows the result of then applying a processing method called white-balancing, which shows an estimate of the colors of the terrain as if illuminated under Earth-like, rather than Martian, lighting.