Auto white balance, it’s a wonderful thing isn’t it? You can shoot away, safe in the knowledge that the camera is working out exactly what color your image should be. Except that it is by no means infallible. Ever wondered why that stunning sunset you shot last night looks strangely cold? In this article we are going to take a look at the mysteries of color temperature.
What is Color Temperature?
Lets start by defining what color temperature is. To do that we need to go back in time to a gentleman called William Thomson aka 1st Baron Kelvin. Kelvin discovered the correct value for absolute zero and put his name to a new scale of temperature measurement, Degrees Kelvin.
It is this scale that is used to measure color temperature and here is how it works. When you apply heat to a perfect black radiating object, it goes through several stages of color as it heats up. Initially it will glow red, this is at a round 2500-3000 degrees on the Kelvin scale. As the temperature of the object increases, the color becomes a colder blue. At 5000k it is a whitish blue, as the temperature goes higher the object becomes even more blue.
Now those photographers amongst you that often select their white balance manually may recognize the figures quoted here. 2500 is around the white balance setting on our camera for tungsten lighting or ordinary light bulbs. 5000 degrees K is a typical setting for daylight, older photographers, from the era of film will also recognize that these are the typical values for daylight film. 5000 degrees Kelvin is defined as the typical color of light at noon, on a sunny day, North America. Beyond 5000K as we have said, the light becomes more blue, overcast days being around 6000-7000K. The light from flash guns going as high as 10000K.
Why is Color Temperature Important to Stills and Video?
So, color temperature is defined by the scale Degrees Kelvin. Why is that important to us as photographer/film maker? Well, unlike our eyes, which can adapt to changes in color more or less instantly, digital sensors, have to be told what the color temperature is. For the most part this is done automatically via the camera’s metering system. However, whilst this is accurate in average scenes, when you get a large block of single color in an image the meter will over compensate for that color. The meter is expecting every scene to be an equivalent of around 18% grey.if you average the color out over the entire scene.
For example, you are shooting a rich golden sunset, the metering system thinks that the scene is way to red/yellow. It will compensate by adding the complimentary colors to the image, in this case cyan and blue. This explains why when you shoot that golden sunset with auto white balance, it looks often looks cold and blueish. This is often very unlike how your remember the scene.
How do we Control Color Temperature?
So, how can we overcome these issues when shooting? Well there are a three main options. Firstly we can use one of the camera’s preset white balances. In the case of the sunset, we know it should be red. We know that the color temperature of red light is around 2500-3000 Degrees Kelvin. Therefore we could set out white balance to the tungsten preset which will be closest to our scene.
At the opposite end of the scale, when you are shooting a scene on a bright but completely overcast day, the image often goes more blue than you would expect, this is because, as we said before, overcast days are usually in the region of 6000 to 7000 degrees Kelvin. One preset we can use here is the shadows preset, this is often around the 6000-7000K mark. If the image is still blue, you can consider the flash preset.
Create your own Presets
The second option for overcoming difficult color temperature is to create our own. Most DSLRs have a setting to measure and create a preset. Typically this is done by placing a pure white card in front of the camera, with the camera pointing in the direction of the scene. A measurement of the color is then made from the camera’s menu system and can often be saved as a preset. This is a very accurate way to get good color balance in your images.
Lastly, there is one fail safe way, in the case of stills, and that is to shoot RAW files. RAW does not embed the white balance date into the file, allow you instead to set it in the post production. If you wish to have a reference file for the scene you will need to show RAW plus JPG. Remember though the JPG file will embed the color balance from the settings, so you may need to apply one of the first two options to get an accurate reference file.
As you can see, color temperature is something that should not be taken for granted. Leave the auto white balance on on your camera and you are not only misrepresenting the color of some of your images, but also missing out on the wide range of creativity that controlling your own color balance can give you.