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Understanding and Setting White Balance
So far we've looked at how cameras measure light and how you can take control of the exposure triangle settings to produce the right amount of brightness. But it's not just the brightness of light that we need to look out for - there's the colour, or temperature, too. It's no good taking a perfectly exposed picture that looks nothing like what you saw because the colours are all wrong! This is something that we can prevent from happening through "white balance". Let's find out more...
What is white balance?
Light is measured by its brightness, but also by its colour. Different light sources cast a different colour on the objects around us. This colour, or 'temperature', can range from the deep orange of artificial tungsten lights to the cool blue of moonlight or shade.
When we describe the colour tone of an image we would call orange 'warm' and blue 'cool'. But, slightly confusingly, when describing the temperature of light (which is measured in degrees Kelvin), the heat increases from orange through to blue!
This is simply because the process of heating certain objects (known as black-body radiators) turns their colour from orange/red heat all the way up to blue heat. The same scale is used for describing the temperature of light. We don't really need to know this in practical terms, but it's useful for avoiding confusion when people talk about a blue light as hot!
So, back to practical matters. Our own eyes are very clever at factoring in the presence of a given colour cast from a light source, and knowing what objects around us are white. For example, a sheet of white paper might actually be bathed in orange light, but our brain and eyes see it as white because we're aware of what white ought to look like.
Digital cameras aren't quite this smart, unfortunately. So we have to manually balance out the colours to compensate for the temperature of the light source. This is what white balance is all about. It could almost be called something like 'colour compensation' instead.
The reference to 'white' is simply because the effect of colour temperature is very evident on a white surface, and we can use this as a guage for what needs changing. There are various ways we can throw a new colour cast over an image, to compensate for that provided by the light source. The result is an image with the correct white balance.
|Correct White Balance:||Incorrect White Balance:|
How to set white balance
There are basically 4 common ways of setting white balance, which are a combination of in-camera and post-production methods. I'm going to list them in order of my preference (others may differ, although few would differ with the number 1 option). Each of these methods will be described lower down the tutorial.
1. Shoot in a Raw file format and adjust the white balance when 'converting' the file in your processing software. I'm aware that to a beginner that last senetence may sound like gibberish. But you should know it basically amounts to changing the settings on 2 colour sliders, without harming image quality at all. It's easy and fast.
2. Shooting in JPEG and using one of the camera white balance presets. These are based on predefined conditions, like daylight and shade, to give you a good enough white balance most of the time.
3. Taking a reading from a 'grey card' - a neutral grey coloured piece of card - which tells your camera that it should look a neutral grey in the current light. A white balance is then automatically selected based on the reading and the rest of your shots will look right.
Check your camera's manual to see how this is done - it will be through the 'custom' white balance option. It's a good approach, but perhaps a bit old-school and long windeed for the average amateur digital photographer.
4. Use the grey pipette tool in a Curves or Levels adjustment layer in Photoshop. Select a grey area in the picture with this tool and the colour tone of the whole image will fall into line. This does reduce image quality so it's the least desirable option.
White balance presets
The in-camera white balance presets each throw a different colour cast over the image to compensate for the light source that they are set up for. The exceptions to this rule are the 'custom' and 'Kelvin' options, both of which require involvement from the photographer to specify the temperature.
Most cameras feature 9 preset options: auto, custom, kelvin, tugsten, fluorescent, daylight, flash, cloudy and shade. A tungsten light source is the coolest dealt with by the preset options (most orange). The rest deal with light sources that increase in warmth right up to shade, which produces a blue colour cast.
So, the white balance presets for these conditions throw a contrasting tone over the image to compensate. In other words, setting tungsten as the white balance will project a blue colour cast (to compensate for the orange light), whilst setting shade as the white balance will project an orange colour cast (to compensate for the blue light).
The auto white balance option makes a best guess based on a reading of the light source(s) throughout the image. It generally works within a slightly limited range, so doesn't tend to perfrom too well in extreme lighting conditions.
Having said that, I tend to leave my camera set to auto (when shooting JPEG), as 80-90% of the time the results are good. Sometimes the other presets can give a colour cast that's a little too strong, whilst auto tends to look quite natural a lot of the time.
Below are some example pictures showing the effects of white balance presets. The more blue the light source, the more of an orange colour cast the camera produces, and vice versa.
In the case of the below image, 'daylight' is the most accurate option. 'Shade' is intended for very blue light, hence the picture looks too orange. Whilst 'tungsten' is intended for very orange light, hence the picture looks a ridiculous blue:
Fine tuning white balance in-camera
To be sure of setting a really accurate white balance in-camera, you can use the 'custom' or 'K' options. Both of these require you to fine tune the settings 'manually'.
Custom: This is the process described above, where a photo of a neutral grey card is taken and used as a guage for the camera to judge the colour temperature of the light in the scene. Once you've set this up you can shoot away knowing the pictures will look right.
On the downside, it requires carrying an extra object - the grey card - and takes up a bit of time. Given the possibility of shooting in Raw, most of use wouldn't use this method very often.
K: This quite simply allows you to dial in the exact colour temperature. It obviously requires a bit of trial and error, but it's quite nice being able to fine tune things with freedom.
A good idea is to begin with one of the presets, like daylight or fluorescent, take a shot and assess the result. You then know the rough ball park you need to be in and you can tweak accordingly.
Fine tuning white balance in a Raw file
I mentioned earlier that this was by far the best option for setting white balance. This is the case for several reasons:
1. It allows you to be highly accurate, setting the colour temperature using precise sliders, looking at a large version of the image on your computer.
2. You can test out different options at your own leisure. Move the sliders back and forth, seeing how different options look on the same photo. Sit back, have a cup of coffee, and perfect the image with no rush.
3. In spite of this being a post-production method, with Raw files we don't harm the image quality by adjusting the colour temperature.
4. It frees you up during the shoot to concentrate on other things. Having one less thing to think about in the heat of the moment is always good.
So, to actually set the colour temperature of a Raw file, open it up in your conversion software (e.g. Adobe Camera Raw) and adjust the Temperature and Tint sliders at the top of the Basic tab. Alternatively you can actually choose a preset option (daylight, cloudy...etc), or use the white balance tool to select a grey point.
Personally my workflow normally involves starting with the white balance tool to get things about right. I then tweak things with the Temperature and Tint sliders to get the final result I'm looking for.
The white balance tool is third from left in the ACR toolbar:
So I hope that, if white balance seemed like a confusing subject before, you now realize that it's actually really simple. All that happens is the camera creates a colour cast to compensate for the colour cast of a certain light source.
You have to tell the camera what colour cast is needed, which can be done by using the in-camera presets, when fine tuning a Raw file or in your post-processing workspace. Raw is the best option for lots of reasons.