White Balance

Author: Quadophile
Published on: 08-12-2004
Views: 39276


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Introduction

An introduction to White Balance, the underused control

The human eye has a remarkable ability to adjust to different light conditions. Not only do our eyes have built-in auto-focus system and auto-exposure capability, but we also have automatic colour balance built into our brains. A white object will appear white to us whether viewed in sunlight or under overcast skies, or indoors under incandescent or fluorescent lighting that is because the human brain has the capability to compensate for such changes in perceived colour. A very efficient system indeed!

The digital camera's image sensor has the daunting task of emulating the human brain and therefore has to adjust colour so that the white appears white in all kinds of lighting conditions, be it fluorescent or tungsten indoors, on a cloudy day or in bright sunshine. Therefore ultimately it all boils down to “Colour Temperature” or what is generally known as “White Balance” in digital camera terminology.

Precise colour capturing and reproduction begins with an optimal white balance. The perceived colour of white often changes based on ambient conditions – outdoor (sunlight which is bluish) is perceived to be cooler, indoor (tungsten which is reddish) is perceived to be warmer and under fluorescent light it is perceived to be greener. Colour Temperature in other words is the ratio of the amount of blue light to the amount of red light; however the green light is ignored. The unit for measuring this ratio is in degree Kelvin (K).

Before we try to go into the finer details of how to set correct white balance we need to know what colour temperature of different light sources really are.

The colour temperature chart above gives approx range in degrees Kelvin for the bulbs, the reason is that the bulbs temperature varies based on brands as well as due to aging, a new bulb will have a higher temperature and an older one lower, hence, the variations. Similarly, the candle light temperature can vary due to size of the flame, which is also approx. It must be noted that the Electronic flash is more or less equal to the colour temperature of average sunlight. The chart above should not be taken as a substitute for a colour meter which professionals use to calculate exact colour temperature in a given situation.