Few people think of light as having color until the color becomes obvious, such as at sunrise and sunset when the sun's low angle causes light to pass through more of the earth's atmosphere, creating visible and often dramatic color. However, regardless of the time of day, natural light has a color temperature, and each color, or hue, of sunlight renders subjects differently. Likewise, household bulbs, candlelight, flashlights, and electronic flashes all have distinct color temperatures.
As humans, our eyes automatically adjust to the changing colors of light so that white appears white, regardless of the type of light in which we view it. Digital image sensors are not, however, as adaptable as the human eye. For example, when the Rebel XSi/450D is set to the Daylight white balance, it renders color in a scene most accurately in the light at noon on a sunny, cloudless day. But at the same setting, it does not render color as accurately at sunset or in a living room because the temperature of the light is different.
Reference For details on setting color temperature using white balance settings, see Chapter 3.
Color temperature is important to understand because different times of day and different light sources have different color temperatures, and to get accurate color in images, the camera must be set to match the temperature of the light in the scene.
Color temperature is measured on the Kelvin temperature scale and is expressed in units, which are abbreviated simply as K. For the camera to render color accurately, the white balance setting must match the specific light in the scene. For example, sunlight on a clear day is considered to be between 5200K and 5500K, so the Daylight white balance setting renders colors accurately in this light.
When learning about color temperatures, keep in mind this general principle: The higher the color temperature is, the cooler
(or bluer) the light; the lower the color temperature is, the warmer (or yellower/redder) the light.
6.9 With the church in the shade and the background sky showing the colors of sunset, the white areas of the church have a characteristic cool tint. I warmed up the color in Photoshop and applied the changes only to the church. Exposure: ISO 100, f/2.8, 1/8000 second.
On the XSi/450D, setting the white balance tells the camera the general range of the light temperature so that it can render white as white, or neutral, in the final image. The more faithful you are in setting the correct White Balance setting or using a Custom White Balance, the less color correction you have to do on the computer later.
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