6.2 COLOR BALANCE

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Although light from the sun or from a light bulb looks white to us, it not only contains a mixture of all colors, it contains these colors in varying proportions. Light from the midday sun, for example, is much bluer than light from a sunrise or a tungsten lamp. To produce what appears to us to be normal or accurate color balance, the image we capture must contain the colors in the original scene. These colors are affected by the color of the light source.

One way to describe the color of a light source is by its color temperature. The color temperature scale is calibrated in degrees kelvin, somewhat like a thermometer that calibrates heat temperatures in degrees centigrade. The color temperature scale ranges from the lower color temperatures of reddish light to the higher color temperatures of bluish light. Daylight contains proportionately more light toward the blue end of the spectrum. Incandescent light contains more toward the red end. That’s why we describe daylight as "cooler" and incandescent light as "warmer."

"White" light actually contains light of different colors and in different proportions, The overall color cast of the light changes as the proportions of the colors change. Although different white light sources have different "colors" you don’t see the subtle differences because your brain compensates automatically.

Image sensors can be balanced to match light of a particular color temperature. This is done using a system called white balance that automatically or manually adjusts the sensor’s relative sensitivity to different colors in order to match the overall color cast of the light it’s recording. The daylight (or outdoor) setting matches the cooler, more bluish color of daylight. The incandescent (or indoor) setting matches the warmer, more reddish color of studio lights.

Daylight	Fluorescent	Incandescent

You can preview color balance by looking at a scene in the LCD monitor. You can also check the color balance of any image you’ve already taken the same way. If you examine the images closely you may notice that white areas in particular have some color cast to them. If so, you may want to adjust white balance for subsequent shots. Many digital cameras offer a number of white balance settings, some for specific lighting situations.

• Auto (the default) works in a wide variety of lighting conditions.
• Manual lets you set white balance manually by aiming the camera at a piece of white paper.
• Sunny is best when photographing outdoors in bright sunlight.
• Incandescent or tungsten is best when photographing indoors under incandescent lights.
• Fluorescent is best when photographing indoors under fluorescent lights.
• Cloudy is best when photographing outdoors in cloudy or overcast conditions.
• Flash is best when photographing with flash.