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| This picture depicts how proper white balance selection makes a marked difference in the overall look of the photo. |
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A photo of flowers with blue color cast. (Simulated)
Understanding Color Temperature White light is not a single, color but is rather a mixture of several colors (violet, indigo, blue, green, yellow, orange and red) . PURE white light is produced through an equal proportion of all these colors, which is very rare indeed. White light often tends to have a slightly blue or a slightly red shade. This shade of white light is frequently described on a scale referred to as “color temperature”. Color temperature is expressed in the unit “K” (kelvin). Values below 5000 K represent a reddish shade of white while those above 5000 K represent a bluish shade of white color. 5000 K itself can be roughly considered neutral white light. This is further depicted in the graph below. It can be seen that at 5000 K, the relative intensity of the all the wavelengths (from 400-800 nm) is fairly equal. At 9000 K, the intensity of the shorter wavelengths (that constitute violet/blue colors) is much higher than that of the longer wavelengths (that make up red). As a result, light of a color temperature of 9000 K is quite blue in color. In the same way, light at 3000 K is red/orange in color.  Now, you might be wondering why we describe a shade of COLOR through the unit of TEMPERATURE instead of the traditional unit of light WAVELENGTH. There is a simple explanation for that. If you are familiar with physics, you might have heard the term “blackbody”. Blackbody is a hypothetical object that is capable of fully absorbing all the electromagnetic radiation (including light) that fall on it. Pure blackbodies do not exist but there are objects that behave like blackbodies at high temperature. The reference object in physics is a platinum wire - but not everyone may be familiar with this, so for the purpose of comprehension, let’s consider the simple example of metallic iron heated to a very high temperature during forgery. As the temperature of iron rises, it first becomes red in color and later it becomes white. The color of white also undergoes changes at different temperatures. Hence, in our photographic color temperature scale, we don’t actually describe the color in relation to temperature itself; rather we compare the color of any kind of white light to the shade of white that a blackbody would emit if it was heated at that particular temperature. The importance of using color temperature lies in the fact that various light sources and lighting conditions closely resemble the various shades of white color emitted by blackbodies at different temperatures. The following table shows some of the light sources/lighting conditions with their corresponding color temperatures. The values of color temperatures are common averages and are subject to variation.
How to use White Balance Presets Most of the modern cameras do not require you to manually fiddle with the color temperature and are equipped with a number of white balance presets. These presets cover the commonly encountered light sources and lighting conditions. The ones included in most cameras, in order of increasing color temperature, are Tungsten, Fluorescent, Daylight, Flash, Cloudy and Shade. Some cameras also allow you to further control the extent of these presets (e.g. -5 to +5 or so). The following table contains a list of white balance presets with an explanation of when to use them.
Advantage of using RAW format (from the WB perspective) Many DSLR’s and some other high-end cameras allow you to render image in RAW format. The use of RAW format has a great advantage from the perspective of white balance. RAW format allows you to capture the photo first and then apply a white balance of your choice AFTER the photo has been taken. (It is also worth mentioning that white balance can also be changed in JPEG images through editing and post-processing. However, the results produced by RAW images are much more impressive). Examples: Auto vs. Manual white balance As mentioned earlier, manually selecting the correct white balance ALWAYS has better results than using Auto White Balance. When auto mode is selected, the tricky colors and lighting often trick the camera into selecting an incorrect white balance. For example, if the image already has too much red, the camera might think that there is enough warmth in the photo and will therefore create a bluish cast in the photo. The following examples show how the correct use of white balance can significantly improve your images. Consider the following photo that I captured in overcast daylight but with Auto WB. It has a slightly blue cast on it.  Here is the same flower which I captured after properly tuning the white balance. The image now shows much more accurate and impressive colors.  In some instances (especially in silhouette shots & sunset/sunrise shots), you may require a deep red/blue shade in the photo which is usually impossible to achieve without manual selection of proper white balance.  The following photographs illustrate the proper use of white balance.   |
