Color Temperature

In essence, color temperature refers to the frequency of color that can be measured from any particular light source. The efficiency of our own visual experience, however, can make the idea of color temperature somewhat confusing.

This is because our eyes and brains have the intrinsic ability to adjust to color shifts such that a white piece of paper will appear white regardless of what type of light is being cast on it. However, color shifts can be much more apparent in situations where there are two or more light sources of differing color temperatures, like the relatively yellow light that emanates through the windows of a house contrasted against the blue light of dusk.

Color temperature is measured in degrees Kelvin. The most important thing to remember about color temperature is that the higher the Kelvin number, the more blue the light source.

The following chart illustrates an approximate color temperature scale (figure 1). Keep in mind that the EOS Rebel's Daylight White Balance is 5300K.

Color Balance

Color balance is achieved when a color recording device (like a camera) renders an image close to how the human eye perceives it. White Balance settings, film type, colored filters and gels can all help to assist the device in achieving "accurate" color. Alternately, you can also throw the color balance off to render a different mood or effect to an image.

White Balance

If you shoot with a film camera and want to achieve color balance in a daylight setting, you would use daylight film to match the color temperature of daylight. If you shoot with a film camera indoors with incandescent lighting, you would either choose Tungsten film or place a Tungsten filter over the lens to balance the color temperature.

If you are shooting digitally, however, achieving color balance in any lighting situation is just a matter of setting the White Balance (WB) in the camera.

To illustrate how the White Balance function works, we decided to take a series of indoor portrait shots using different color temperature settings. We started by taking a snapshot with a point and shoot digital camera.

Since the built-in flash of the EOS Rebel is balanced to sun light, we set the White Balance accordingly (the "sun" icon). (Most digital cameras have a few White Balance settings that you can adjust manually, the default for the Rebel out of the box is the Auto setting.)

We activated the flash, set the camera to Program (automatic exposure) and took a shot of our model in front of a sweep of white background paper (figure 2).

Although the color temperature is balanced in Figure 2, it also reveals the common problems you get from this type of on-camera flash lighting. Since our light source (the flash) is small and positioned just above the camera, the result is both dimensionally flat and high in contrast. The eyes look darker than they actually are, the reflections in the eyes are unnaturally centered and tiny, and there is a distracting shadow is rendered behind the model's head.

To improve the lighting, we decided to light the model with a large, diffused light source for a more natural-looking effect. For this next shot, we set up a Large Starlite Kit and positioned it to the right of our model at approximately 45-degrees. The Large Starlite Kit uses a 1000-watt Tungsten lamp that's color-balanced to about 3200-degrees Kelvin, about 2300 degrees warmer than daylight or flash.

For comparison purposes, however, we decided to use the same WB setting as before (Daylight). In order to select this White Balance preset, first press the WB button and then jog the Selection Dial until the "sun" icon appears in the control panel (figures 3 & 4).

Once the lighting was in place, we made a few more adjustments to the camera. Since we wanted the model's eyes to be in sharp focus and for the background to be relatively soft, we set the Exposure and Focus modes to Manual, opened the aperture up to f/4 (the wider the aperture, the more selective the focus), and set the shutter speed to 1/60th of a second to render a good exposure. We then set the ISO to its lowest setting (100), set the Resolution to TIFF, focused and took a shot (figures 5 & 6).

The result shows a tremendous difference in the lighting of the shot. The SilverDome soft box from the Starlite Kit had diffused the light to render a soft, wrap-around light on the model's face. The effect is that of a window light. And since the lamp in the Starlite Kit is continuously on, it forces the model's pupils to close down to reveal more color in his irises. Notice the natural-looking catch-light in his eyes as compared to figure 2.

The color of the shot, however, is much warmer than in figure 2 because the camera recorded the relatively warm light from the Starlite (3200K) at a cooler daylight/flash setting (5500K). Remember, the lower the color temperature, the more yellow the light (see chart above).

Our next step was to return the camera to the tungsten (the "bulb" icon) White Balance setting and shoot another shot (figures 7, 8 & 9).

With the proper setting for the lighting we used the result now looks like we see it with our eyes.

Notice how the model's skin tone looks more natural and that the blue in his eyes is truer in color.

To illustrate other Preset WB settings against this Tungsten light source, we first switched the preset to fluorescent light. Fluorescent light is very close to balancing the color temperature of warm fluorescent lighting, which is relatively green (figures 10, 11, and 12).

Notice how the colorcast resulted in a strong magenta. Again, this is because when the camera is set to fluorescent light. It is in effect ready to neutralize light with a relatively green cast to it. Think of the camera as adding a specific color to neutralize the color of the light source.

Yet when it captures light that lacks the green cast, it is stuck with an image that is, in effect, recorded with a magenta filter over its lens. The color wheel below illustrates these complementary colors (figure 13).

Finally, we took a shot with the white balance set to the "shade" setting, which would be a good setting to use in the open-shade of a sunny day. The open-shade of a sunny day is actually slightly bluer in temperature than that of an overcast day (6500) because the ambient light coming from the sky is blue on a sunny day, rather than gray (relatively neutral) on a cloudy day (figures 14, 15, and 16).

Notice how warm the shot is now! The White Balance setting is about 4300 degrees cooler than that of the Starlite, making the result extremely warm. And although the color temperature in this image is not rendered "correctly", it does give the shot a different mood. In fact, this image ended up being one of the model's favorites.

As was demonstrated here, it is important to know how to adjust the White Balance of your Canon EOS Rebel to render accurate color as well as to create special effects.