For many newcomers to photography white balance seems to be a mystery. The reason is probably, that most people don’t know that light can have a distinct color. In our perception light is always white or, more precisely, without color (I’m talking about light that illuminates our surroundings, not of LEDs or other light sources that can have a distinct color). Actually (natural) light has a range of colors from yellow to blue. Our brain automatically adapts to changing light colors. A camera, however. truthfully records the color of the light. Without proper white balancing the resulting images would have a color cast if the light was not white.
Color temperature
The words color and temperature seem to describe completely different concepts. But in science the color of light is measured in Kelvin (K), which is a temperature scale (I leave it to you to look up the physical relationship between color and temperature). For practical purposes it is sufficient to know, that red light is about 2000 k, yellow is about 3200 K and sunlight around noon is approximately 5500 K (which is actually white). On an overcast day the light is slightly bluish (about 6500 K) and the light e.g. in the shade of a tall building on a sunny, cloudless day can be even more bluish (about 7500 K). The illustration below shows the relation.
White balance settings
In theory the white balance settings should correspond to the color of the light. On a cloudy day you should use the 6500 K setting, on a sunny day between about 10 a.m. and about 4 p.m. you should use 5500 K and so on. However, it is quite cumbersome to change the white balance (short WB) whenever the light color changes and above all it is almost impossible for our brain to determine that the light color has changed. Therefore all cameras provide the Automatic White Balance (AWB) function.
In our experience AWB works quite well most of the time. The featured image above is a good example. Since the image is dominated by red and yellow, it is very difficult for the camera to determine a correct white balance. The reason is, that the camera does not “know” whether the light or the subject itself is red (an average subject has many different colors which makes it easier to detect the color of the light that illuminates the subject). But despite this compliccation the white balance is quite good:
At closer inspection there is a slight bluish cast to the white mask. This color cast could be removed in post processing, but personally I quite like the color contrast between the red/yellow tones and the bluish mask.
This image is an extreme example, as mentioned above. Average subjects sould present no problems for the automatic white balance. However, especially yellow subjects somtimes seem to result in unsatisfactory colors when using AWB. The following image is an example:
The foliage of these birch trees in autumn was a bright, intense yellow which the AWB function obviously mistook for yellow light and consequently tried to compensate for the supposed color cast. This resulted in muted yellow tones and a distinct bluish cast on the tree trunks. Since this image was taken on a cloudy day the white balance setting “Cloudy” resulted in the following image:
This looks much more natural and corresponds to what we actually saw.
If you shoot RAWs you don’t need to worry about white balance at all. You can use any white balance setting you like in post processing, regardless of the white balance setting in your camera. That’s the beauty of RAW files.
Conclusion
The AWB function results in good color rendition most of the time. Average subjects that contain a lot of different colors don’t present any problems at all. Some care should be taken whenever a color dominates the image like the yellow foliage in the example above. In those cases you should check the image on the display and select another WB setting if necessary. Alternatively you could use RAW images and never think about white balance again …
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