Project: White Balance and Overall Colour

An essential setting on your camera is for white balance, but why is this so?

Apart from the colours that objects and surfaces have, and apart from strongly coloured lights, we expect the ambient light anywhere to seem neutral, with no particular colour. In other words, we don’t even think about the colour of the overall lighting. This is because our eyes adapt very well and quickly, to changed in the colour of the light. There are changes within sunlight depending on whether the sun is high or near the horizon, and between sunlight and tungsten lighting in your home. But our eyes and brain process the view so well that we ‘Neutralise’ the differences. The camera’s sensor however, is literal. It records all the differences in colour, and will make no adaptation. For this reason, the camera needs to be set to an appropriate colour balance.

Digital camera’s have a system similar to the human eye. This is known as the Automatic white balance setting. The red, green and blue signals are analysed for any overall dominant colour present in all parts of the image. This dominant colour is removed by varying amounts according to the colour and its strength. If the analysis is too simple, a subject with a strong dominance in one colour, such as autumn leaves or an expanse of ocean, would be wrongly white balanced so, in may systems, the highlights and shadows are also analysed and used to temper any removal or dominant colour. However, some digital cameras often have great difficulty with auto white balance (AWB). They can on occasions, create unsightly blue, orange, or even green colour casts. Understanding digital white balance can help you avoid these colour casts, thereby improving your photos under a wider range of lighting conditions.

Sunlight is our visual standard for colour. In the middle of the day, it seems colourless. We usually call it ‘White’. This is our benchmark for ‘Normal, Neutral’ lighting. Sunlight ranges from white to red in a colourful sunset or sunrise. In the shade on a clear sunny day, the light can take a blue-ish cast of the sky. This progression of colours is called the ‘Colour Temperature Scale’.

Colour temperature describes the spectrum of light which is radiated from a “blackbody” with that surface temperature. A blackbody is an object which absorbs all incident light, neither reflecting it nor allowing it to pass through. An example of this is heating Iron. When you heat Iron, it will first become red, then yellow, then white. Also known as White hot. At even higher temperatures, some materials can turn blue, then melt or vaporise.

Colour temperature is a useful description of light for photographers, even if we never deal with true blackbodies. Fortunately, light sources such as daylight and tungsten bulbs closely mimic the distribution of light created by blackbodies, although others such as fluorescent and most commercial lighting depart from blackbodies significantly.

With photography, the most important colour temperature is that of the sun. On this scale, it can be given a value, in degrees of temperature. The temperature is measured in degrees Kelvin. Similar to Celsius, but starting at the lowest possible temperature called ‘Absolute Zero’.

Noon sunlight is generally accepted to be between

5400K – 5500K

When the sun becomes lower in the sky in the late afternoon, the colour temperature also lowers to approx. 4000K.

At sunset, depending on the sky conditions, it can be approx. 3000K.

The reflected light from a blue sky ( In other words, in the shade ) it can be higher than 6500K.

There may be some confusion, as it is natural to describe red colours as ‘Warm’ and blue colours as ‘Cool’, whereas, the colour temperatures are in fact the opposite. Be aware when you are talking about the visual effect and not the colour temperature.

Since photographers never use the term ‘colour temperature’ to refer to a true blackbody light source, the term is implied to be a “correlated colour temperature” with a similarly coloured blackbody. The following table is a rule-of-thumb guide to the correlated colour temperature of some common light sources:

Colour Temperature Light Source
1000-2000 K  Candlelight
2500-3500 K  Tungsten Bulb (household variety)
3000-4000 K  Sunrise/Sunset (clear sky)
4000-5000 K  Fluorescent Lamps
5000-5500 K  Electronic Flash
5000-6500 K  Daylight with Clear Sky (sun overhead)
6500-8000 K  Moderately Overcast Sky
9000-10000 K  Shade or Heavily Overcast Sky

 

There are ways of adjusting the colour balance on your camera.

  • Auto White Balance: Using auto white balance means letting your camera’s processor to sort out the whites for itself.
  • Pre-determined Setting: Using this setting means that you have to judge for yourself, what white balance is needed for a specific scene. You have the choice to choose between Incandescent, Cloudy, Shade, Fluorescent, Tungsten.
  • WB Preset: With this setting, you help your camera measure a white patch ( Example, White piece of card )

 

Auto White Balance
Custom
Kelvin
Tungsten
Fluorescent
Daylight
Flash
Cloudy
Shade

Below is an example of different White Balance settings, taken from the website Digital-Photography-School.com.

 

References:  

http://www.cambridgeincolour.com/tutorials/camera-sensors.htm

http://www.digital-photography-school.com/introduction-to-white-balance/

Digital Photography Master Class, Tom Ang, Dorling Kindersley Limited, London 2008. Page 169-169.

ISBN: 9781409333906

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