Any discussion of the white balance must begin with colour temperature, an attribute of light that's a way of quantifying lights overall basic colour.
The term "colour temperature" is borrowed from physics, where it relates to the spectrum of light that's radiated from a theoretical object called a black body. As you heat up this object, it changes the colour that it emits. Terms like red hot and white hot are manifestations of this principle. As an example, if you heat a piece of metal, first it becomes dark red. As it becomes hotter, it turns yellow. Finally, as it becomes hotter still, it turns more bluish white, or what some might consider white.
In photography, however, the terminology we use for colour temperature (warm or cool for example) is just the opposite of its meaning in physics. Photographers consider blue to be cool and red to be warm.
White balance is a process of adjusting colour cast so that objects which appear white in person are rendered white in your photo. For example, take a sheet of white paper and place it under an indoor incandescent light - it takes on an orange tint - warm. Take that same paper and place it under fluorescent lights it appears much whiter, or even slightly blue - cold. Having the incorrect white balance is responsible for making photos appear very orange when indoors, or photos taken at dawn or dusk appear blue.
Most of the time modern cameras do a pretty good job of selecting the correct white balance profile to use and we need not worry about it, however, there are times when the camera gets confused.
The most common colour profiles and corresponding temperatures and uses are shown in the illustration below.
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White Balance Presets
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|Auto (AWB) - A simple fail-safe for snapshots, but can vary from shot to shot depending on how the camera meters the scene.|
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|Incandescent - Used for domestic indoor lighting and will colour match more effectively, eliminating the orange colour from indoor photos.|
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|Fluorescent - for use when photographing under fluorescent lighting, however there are many types and this setting often has many options.|
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|Direct Sunlight - Gives neutral colours under midday sun. Often used as a reference for "normal"|
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|Flash - Flash guns have a cold feel about them, using this setting warms them up a little.|
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|Shade - For shooting outdoors in shady conditions, under blue skies but not direct sun light|
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|Cloud - For shooting outdoors in cloudy conditions, overcast with grey skies and a dull light cast|
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|K - Some cameras allow manual colour selection from a list of temperatures in Kelvin.|
Colour temperature describes the spectrum of light which is radiated from a black body with that surface temperature. A black body is an object which absorbs all incident light - neither reflecting it nor allowing it to pass through.
Light sources such as natural daylight and tungsten bulbs closely mimic the light created by blackbodies. Other light sources such as fluorescent and most commercial lighting differ greatly. Photographers use the term colour temperature to refer to correlated colour temperature with a similarly coloured black body. The following table is a general guide to the correlated colour temperature of some common light sources.
|Color Temperature||Light Source|
|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|
Fortunately, most digital cameras contain a variety of preset white balances, so you do not have to deal with colour temperature.
Fixing White Balance
The easiest method is to select the correct colour profile on the camera; however, it may be required to do so afterwards in post-processing.
Most image editing packages have a white balance feature which allows selection from a list of presets, similar to on the camera. There is also often a manual mode, allowing you to manually specify what "white" is and what "black" is. From this, it can generate a colour profile curve which can then be fine-tuned. It should be noted that this option is for advanced users as incorrect settings here will have disastrous results.
White balance adjustments are much easier when you shoot in RAW as the raw files contain the raw data - the camera has not tried to adjust the colour balance, and there is much more information to work with than a JPEG which has a lot of detail stripped out. You can still change the white balance when shooting in JPEG but only by slight amounts. Large amounts will cause the quality to degrade.
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Most, if not all post-processing software such as Adobe Photoshop or Adobe Lightroom comes with an auto white balance option.
In Lightroom, you can adjust the white balance in the selected image by selecting an option from the White Balance dropdown list. You can use this to fix the image or you can use it as a starting point and then fine-tune the results.
You can also manually adjust the Temp slider to add warmth or remove it from the image. Drag the slider to the left to add a blue tint to the image (to cool it down), or to the right to add a yellow tint to it to warm the image.
Use the Tint slider to balance out any excess magenta or green in the image. Drag towards the right to add magenta to the image cancelling out any green tint and drag to the left to add a green tint cancelling out any unwanted magenta.