Understanding white balance and color temperature.
In video production, as in life, we often find ourselves concentrating on the big picture, only to miss the small details that can keep us from achieving our goal. One of these fundamental details is white balance. Despite advances in video editing software that allow us to 'fix it in post,' white balance remains an important component to understand early in the production process if we're to end up with the best possible video.
White Balance Defined
White balance in video production boils down to the concept of color temperature. Every source of light gives off a unique color temperature as seen by a video camera. We may not recognize these differences ourselves because our eyes and brain have an amazing capacity to make adjustments. For example, you see white as white in just about any setting, but your camcorder needs a bit of help. When you white balance a video camera, you're helping it adjust the ratios of all of the colors it sees against true white - the combination of all color - so that it records the truest possible color in a scene.
Measuring Color Temperature
The scale used to measure color temperature is in degrees Kelvin. A light source with a higher color temperature - a higher Kelvin value - has more blue light than a light source with a lower color temperature - a lower Kelvin value. This means a cooler light has a higher color temperature. Confused? That's because this Kelvin scale runs counter to what we think of when we measure air temperature on a standard thermometer. Figure 1 shows the approximate Kelvin color temperature of some common light sources you may find yourself shooting with in video production.
If you're shooting outdoors in bright sunlight, the camcorder needs to adjust to that particular color temperature to represent the colors you see accurately on tape. If you then move indoors to shoot a new scene, the camera needs to readjust to the new light source and new color temperature. This process of adjusting is called white balancing and there are a number of ways to accomplish it.
Is it really a big deal if you mix up your white balance settings? In Figure 2, the image on the left shows what can happen if a camcorder recording indoors, with available ceiling and table lights, is white balanced for outdoor light. The camera will expect more blue light and less red so it will adjust itself to be more sensitive to blue. You end up with a reddish or yellowish image. If you set the camcorder with an indoor white balance setting but shoot outside in the bright sun, the camera will be more sensitive to the red light resulting in a heavily bluish image, as seen in the image on the right. It's clear that not being aware of your white balance setting can produce very disappointing results.
Manual White Balance
There are a number of white balance options on camcorders today, which you choose depends upon your specific shooting environment. Manual white balance is usually your best shot at getting the most accurate color reproduction. Let's say you're shooting a child playing in her bedroom and you want the color of the scene recorded to tape just as you see it. Set your camcorder in manual white balance mode. Place a small white card, white sheet of paper or white fabric near your subject, lit by the main light source in the room. In this case probably a ceiling light or table lamp. Zoom in and fill your viewfinder with the white card and activate the white balance. The camera will give you an indication in your viewfinder when the white balance is complete, typically in just a couple of seconds. By doing this, you're showing the camera the color white, lit by the main light source in the room. When you press the white balance button, the camcorder will adjust and balance the ratios of colors, using white as a reference. Hint: Be sure the white you use is true white. The camcorder will believe whatever you point at is white during a manual white balance. If you white balance on an off-white color, you'll likely get a poor reproduction of color. Another hint: Be sure the iris of your camcorder lens is open or you may not be able to complete a manual white balance at all.
Preset White Balance
While manual white balance provides the most accurate setting, many camcorders offer presets which do a pretty good job. Most camcorders have several preset positions, programmed at the factory, to help in achieving an accurate color balance. Each preset has a stored color temperature in its memory or an internal filter activated by the flip of a switch. Often, these presets are noted on the camcorder by symbols of a light bulb and a sun. Clicking to the light bulb position sets the camcorder to read an indoor color temperature (somewhere in the 3,000 to 3,500-degrees Kelvin range). Click to the sun or outdoor setting and the camera adjusts to expect a color temperature in the 5,600 to 6,000-degrees Kelvin range. Presets are nice for saving time if you're moving in and out of different light sources and locations but, again, this is not as accurate as performing a manual white balance.
Automatic White Balance
The automatic white balance setting is handy when action or time makes it impractical to white balance the camera yourself manually. Here, the camcorder's internal sensors try to measure as best they can the color temperature of the scene and then apply all of the mathematics to make the shot look good. Camera technology has come a long way, but don't expect the auto function to get your color correct one hundred percent of the time, especially if you're shooting in locations with multiple light sources. Use the automatic white balance only if time doesn't permit a manual white balance.
While it is possible to adjust color during the editing process after shooting is complete, 'fix it in post' is a poor approach to good quality video. Take the time to think about your light source, it's color temperature and get an accurate white balance. This is time well spent to capture the best possible video.
Sidebar Two: Trick of the Trade
Since a camcorder will attempt to white balance on whatever color you focus it on, you can experiment with white balancing the camera on different colors, other than white. Typically, a video image will wash to the opposite of itself on the color wheel. As an example, if you're shooting a great sunrise and you'd like to be sure to capture the deeper reds and oranges of the scene, you can do a manual white balance by focusing on a sheet of light blue paper. This tricks the camcorder into favoring the reds and yellows. Since television sets produce images as high as 9,000-degrees Kelvin or more - a very cold, blue color - it can sometimes help to 'warm up' your shots while shooting. Keep in mind this takes practice. I have a color wheel taped to the inside of a camera bag so that I can recall how to cheat the color correctly. It's a good idea to hook up to a color monitor or television when using this technique. Please don't start experimenting with this for the first time when shooting a wedding video.