Introduction to White Balance in Digital SLR Photography

[AHutch]

White Balance, next to Exposure concepts, is one of the most important concepts you will learn in digital SLR photography. It's one thing to understand all the inner workings and features of your camera but understanding how to use your digital SLR to take great pictures is what separates the "men from the boys"! And understanding white balance is part of that process. Many people starting out with digital SLR photography will ignore white balance and then wonder why some of their pictures have an orange hue to them for example, or why they can’t get the effect right for that stunning sunset. I must admit that this article is long! But the subject of white balance can be a tricky subject to grasp and given its importance, it is necessary to give it the due attention it deserves. To take quality pictures, you need to understand white balance. So buckle yourself in!

Use White Balance for Corrections & Creative Control

The white balance setting on a digital SLR camera is a setting that allows you to make choices about the overall "color cast" of the photograph, both from the perspective of making corrections and from the perspective of creative control. More specifically, it is a setting that helps the camera "balance" the overall light in a scene so that the scene will look more "natural" as well as allowing you as the photographer to specify the overall "color cast" you desire for a scene. A classic example of this type of creative control is with a sunset whereby you want the photograph to appear with an overall reddish-orange color in order to capture the intensity of the scene.

Put simply, white balance settings help the digital SLR capture the colors in a scene accurately and can also be used creatively to adjust the overall colors in a scene.

Color Cast and the Color of Light

"Color cast" refers to the overall color of a photograph and more specifically, the color of the overall light that is striking your subject. What do I mean by the "color of light"? Our eyes are wonderful things. All light has a certain color to it that our eyes don't always notice. When we look at a white object for instance, we see that object as white regardless of whether we are looking at it under daylight, under shade or under the light from an incandescent light bulb. Unfortunately even the most complex digital SLR is not as sophisticated as our eyes. The camera, or more specifically the image sensor, will "see" that same white object as having a particular color cast to it and thus render it either white or with a red or blue tone depending on the color of the light that is illuminating it.

To understand white balance and the color of light we need to go back to elementary school and talk about primary colors. Digital SLRs use the primary colors of Red, Green and Blue to capture the colors of any object you are photographing. This is commonly known as RGB and those letters are in that order for a reason because they represent a spectrum of colors from red at one end of the spectrum to blue at the other end, with green in the middle. In photography, red colors are considered "warm" (think of a flame) and blue colors are considered "cool" (think of ice). And green is considered "neutral". Further, each of the red, green and blue colors have a range of tones that are captured by the image sensor of the camera. Now, the "true" tone of a particular object will be effected by the color, or more specifically the "color temperature" of the light hitting it. Therefore the image sensor of the camera will not always capture the "true" color of the object unless the white balance is set to make the correct adjustment because the image sensor, unlike our eyes, cannot by itself filter out the color of the light hitting the object. Our eyes automatically filter out any color cast in our environment but the image sensor of a digital camera cannot do that unless we tell it what to do. Again looking at the example of a sunset, ever notice that a well-done photograph of a sunset looks way more spectacular than seeing an actual sunset? This is because our eyes filter out the overall reddish-orange of the scene while the camera does not and it is this overall reddish-orange color cast that makes a spectacular sunset photograph.

All Colors Have a Temperature

When photographers talk about the color of the light hitting their subject or the color of the overall light of a scene they refer to it as "color temperature". It is measured in Kelvin (K) or degrees Kelvin (oK) and is a number generally between 1000 and 30000. For instance, light under shade generally has a color temperature somewhere between 7000K and 8000K, while daylight is about 5000K. These numbers are opposite to the temperature scale. The lower the number, the warmer (redder) the light and the higher the number the cooler (bluer) the light. Here are some typical color temperatures for different types of lighting (please note that these numbers are approximate):

• Match/Candle .............................................. 1800K
• Sunrise/Sunset ............................................ 2000K
• 75-Watt Tungsten light bulb ........................... 2900K
• Sunlight - Early Morning/Late Afternoon .......... 4300K
• Average Summer sunlight at noon .................. 5500K
• Overcast sky ................................................ 6000K
• Light summer shade ..................................... 7000K
• Average summer shade ................................ 8000K

While the image sensor is not as good as our eyes at filtering out color casts over a scene, digital SLR manufacturers have figured out how to use complex software to allow the camera to calculate the overall color temperature of the light in a scene and determine the best way to balance that color. So if it detects that a scene has too much red colored/warm light (that is, the color temperature of the light is too low) it will attempt to make an adjustment by "adding" more blue to the scene (by increasing the color temperature) and thereby balancing the color of the light and making it more "natural". This is what happens when the camera is set to Auto White Balance (AWB).

A digital SLR camera allows you to choose various settings for the White Balance. Here are the typical white balance settings:



Asking The Camera to Adjust the Color of the Light

When we choose a particular white balance setting on the digital SLR camera other than AWB, what we are doing is one of two things. Either we are telling the camera what we believe to be the color temperature of the ambient light and asking it to make the necessary correction OR we are telling the camera what we want the camera to believe is the color temperature of the ambient light. Therefore if we set our digital SLR to “shade”, we are telling the camera to read the light as if the color temperature is approximately 7000K. Since this is overly cool, the camera will attempt to balance the light by decreasing color temperature by about 2000K in order to bring it closer to a more "natural" color temperature, approximately 5000K. A simpler way to look at it is, a “shade” setting is telling the camera that the scene is overly cool (blue) and therefore please add more red to warm it up and make it more natural looking. This is an example of a “corrective” purpose for white balance setting.

An example of a “creative” purpose for adjusting white balance is in situation when you don’t necessarily want the light balanced or neutral but instead you wish to add more warmth or coolness to a scene. If you wanted to add more warmth to a scene, you would do this by telling the camera that the scene is cool and therefore set the white balance at “cloudy”, “shade” or “flash”. This would cause the camera to automatically add extra warmth to the scene by adding red (decreasing the color temperature) because it thinks the scene is too cool regardless of whether it actually is or not.

Have a look at these three photos:


Image A - Fluorescent Setting


Image B - Auto White Balance (AWB) Setting


Image C - Tungsten Setting

Image B in the middle was taken with the AWB setting and gives the most natural color.

Image A on top was taken with the Fluorescent setting. With this setting the camera is being told that the light is cool and therefore tries to warm up the overall color cast.

Image C on the bottom was taken with the Tungsten setting. With this setting the camera is being told that the light is warm and therefore tries to cool down the overall color cast.

As you can see, the differences in these photos are somewhat subtle and in this case it becomes a matter of personal preference. This is where creative control comes in.

To summarize:

All ambient light has a color temperature ranging from approximately 1000K at the warm/red end of the spectrum to 30000K at the cool/blue end of the spectrum. This can cause red or blue color casts over a scene which our eyes would naturally filter out.

White balance is a setting that helps the camera "balance" the overall light in a scene by reducing any red or blue color cast so that the scene will look more "natural".

In AWB, the camera will attempt to bring the overall color cast to the "middle", a more "natural" setting if it reads the scene as too warm or too cool.

White balance is also a setting that allows you as the photographer to specify the overall "color cast" you desire for a scene thus giving you greater creative control.

If you wish to add warmth to the scene, set the white balance to a cool setting

If you wish add coolness to the scene, set the white balance to a warm setting

[Hill Country Hack]

A very good write up. I learned a lot and will experiment.

[AHutch]

Originally Posted by Hill Country Hack

A very good write up. I learned a lot and will experiment.

Hope it helps! Just remember - if you are trying to correct, try to match the setting to the light OR, if you are trying to be creative, do the opposite by setting WB cool if you want to add warmth and setting it warm if you want to add coolness.

Bear in mind that you can always use the "opposite rule" whether you are trying to correct or trying to be creative - just set the WB to the opposite of what you want to achieve.