Sunday, 24 September 2006

White Balance

Three images showing different white balance settings

Digital cameras have one very interesting advantage over good old film cameras: you can adjust settings that you would normally have adjusted by changing film. An obvious one is the ISO setting: one shot can be taken at 100 ASA, the next one at 400. A less obvious but very important setting is the white balance. This setting is meant to adjust the colour balance in different types of light so that white areas actually come out white. If you get the white balance wrong, the white areas in your shot will come out yellow or blue, depending which way you got it wrong.

Most DSLR cameras and some high end compact digital ones allow you to override the white balance, typically by offering a presets for tungsten or fluorescent light, cloudy or shade conditions, etc. But your specific lighting conditions don’t always match a preset. Some cameras allow you to provide a sun temperature equivalent in Kelvin but this is confusing if you are not an astronomer or a physicist. Finally some cameras allow you to specify a custom white balance by giving them a reference. I had never used this setting as I wasn’t too sure how it worked on my camera, until today when I picked up a copy of Mac User that has a very simple and straightforward explanation.

I decided that the subject for experimentation would be my bedroom, complete with unmade bed. Not that I want to pretend I am Tracey Emin but the wall behind my bed is the best white reference in my flat. To make my life easier, I composed the shot to ensure a large area of white wall would cover the centre of the image, as this is the area the camera will use as white reference.

  • The first picture is taken using the automatic white balance setting. Although the camera tried to compensate for the yellow hue produced by the tungsten light, it is still very yellow.
  • The second picture is taken with a preset white balance for tungsten light, which should be the right setting in this case. unfortunately, and probably because of the lamp shade that modifies the light, it is still quite yellow. Although, in this case, when seen on its own and in the original light, the mind adjusts and makes you think it is actually white.
  • The last picture was taken using the custom white balance seting and the previous picture as a reference. This time it is really white: I verified this by using the colour picker tool in Photoshop. The funny thing though is that seeing the shot on the camera’s LCD screen, on its own and just after the previous one, the mind plays tricks again and makes you think it is blue-ish.

Using a custom white balance produces great results. The only complication is that you have to take a reference shot and adjust the setting every time you change light condition but it is easier and quicker than doing that in Photoshop afterwards, especially if you take several shots in the same lighting conditions. Also note that, because it consists in comparing the balance of primary colours in a reference subject, this reference doesn’t have to be pure white, it can be light grey. So a photographic 18% grey card is an ideal reference object.

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