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Human eyes adapt to different types of illumination so that what we see always looks normally coloured, that’s not the way a camera works.
In a car with slightly tinted windows, your eye filters out the tint so that after a few moments you don’t realise it’s there, but if you open the window things outside look tinted until your eye readjusts. Car windows with a tint of green give everything a magenta colour cast when opened. The eye and brain adjust the sense of sight to neutralise the dominant colourcast. The light illuminating a subject will give it a colourcast and the camera will reproduce it in the image.
Changing the camera’s white balance adjusts its colour sensitivity to remove the colourcast so that a white subject will be white in the image. Digital cameras can normally set the white balance automatically but this may be inadequate for some situations. Most digital cameras allow the white balance to be set to suit a particular type of light source by selecting symbols on the LCD monitor.
The instruction book will describe a means to manually set a more accurate balance by pointing the camera at a true white or pale neutral grey surface in the colourcast ambient light and pressing the shutter or a dedicated button. The camera will then remove that colourcast from future exposures. If the light source changes use the automatic balance or reset manually. The shade of a light source is expressed as its color Temperature in Kelvin units. The list below shows the approximate colour temperature of light sources.
|Shade in daylight around||6500 K|
|Average midday sun||5500 K|
|Early morning / evening||3500 K|
|Tungsten lights||3000 K|
|Sunrise and sunset||2500 K|
|Candle light||2000 K|
|Fluorescent lights will vary|
Lower K value light produces a warmer image with a red, orange or yellow cast, and higher value a cold blue cast.
A foundry shot with daylight through the foundry roof giving a blue cast. On the right an image colour balanced. Is the hard world of a foundry better in cold or warm colours?
cameras using film require a filter on the lens to correct colourcast. A very light blue filter corrects a warm cast and light red a cold cast. Filter selection depends on experiment, experience and a large range of filters.
Using white balance means you can have pictures with a neutral color whatever the ambient light. However white balancing can spoil the photograph, for example a candlelit scene would look wrong in a neutral color. A family sitting around a fire should have a warm cast. So use white balance only for a good reason.
It is often necessary to change white balance for fluorescent tube lighting as it varies considerably in colour.
If you handle your photos on a computer with a suitable program, such as Photoshop, white balance can be easily corrected so you can be less attentive to it when you shoot.
An example of an image that if white balanced, would have lost all atmosphere an feeling.