Project: White Balance and Overall Colour

The exercise as described was very similar to an exercise in the Art of Photography (described here) so I thought I would do a variation and delve a bit deeper into how my camera treats white balance.

I started with the manual. It described the camera’s approach to setting white balance with an auto setting and six presets for sunshine, cloudy, tungsten and fluorescent lighting, flash and shade. The manual gives the colour temperature corresponding to each preset. There is also the possibility to set a custom white balance or adjust by setting the colour temperature. The latter might be useful if a light source of a know colour temperature is used. The manual gives a warning about calibration differences if using a colour temperature meter.

The Fridge

The first set of pictures is of the kitchen fridge. The lighting was a mixture of cloudy daylight and tungsten halogen, with the daylight dominant. Exposure was maintained at 1/10 sec at f5.6 and ISO800 for all these. The first was with the white balance set to auto:

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Next up was tungsten (3200K):

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Then a custom setting was established by taking a picture of the fridge and using this to establish the white balance:

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Viewed subjectively, the auto and custom settings have produced correct looking pictures, the tungsten version is too cold, indicating that the room lighting was not contributing much to the overall light level.

Punch

This hole punch was placed in the living room window sill, so the dominant lighting was from the cloudy outdoors. This was taken with auto, cloudy settings, then a custom white balance taken on the white woodwork:

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The auto and custom look quite natural whereas the cloudy setting has a slight blue-green cast.

I then tried using different colour temperature settings, starting with 2500, then 6000 and finally 10000:

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as expected the 2500 is very blue (to compensate for the redness that light of that colour temperature would have), 6000 is about right (this is the colour temperature for the cloudy preset) and 10000 is too warm.

Limitation of auto white balance

While studying the Art of Photography, I spotted that the auto setting can be fooled (see here). The next pictures explore this further.

Using the auto setting, I took the following two pictures of the blue punch and a yellow Marmite teapot lid against a green tablecloth. The exposure was the same for both pictures:

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The lighting was from outside with an overcast sky so I selected the cloudy setting for these two:

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This has rendered the green tablecloth much more faithfully and consistently.

The relative proportions also affect how the camera works on auto as the next set demonstrates. The first pair were taken with the auto white balance and the same exposure. The only difference is how much of the frame the green car occupies:

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Then with the white balance set to cloudy:

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This has shown some interesting results, mainly that the auto white balance cannot always be trusted. Not only does the lighting affect the colour of scene, the colours of the scene can affect how the camera processes it.

Probably the most accurate way of setting the camera’s white balance is to use the custom setting. I did this on some white objects in the scene for this exercise. In fact, I deliberately chose scenes with an area of white to set a custom white balance against. An alternative would be to use a grey card. The setting only needs doing once providing the lighting conditions don’t change so it can be set at the start of a shoot.

A scene dominated by bold primaries can fool the auto setting so these should trigger a warning that an alternative setting should be used.

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