How about a mini-lecture on white balance? What you see is not always what you see. In other words, what your mind perceives is not always what is really there. Color is one of those cases. The human eye (actually the human brain but you know what I mean) is very good at auto white balance. It’s so good at white balancing that most people don’t even realize that it is happening.
Every different type of light source produces light of a different color. The same object lit by those different sources will reflect different colors. A white shirt in daylight will look bluish but under an incandescent light will look amber. The purpose of white balancing is to keep white (or grey) objects looking white. If white looks white, then the other colors in the scene should look correct also.
Color temperature:
From Wikipedia - “The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source”. As a black-body heats up, it’s radiant color changes. From red to yellow to blue. A black-body can be a lump of iron or the filament in a light bulb. Color temperature is measured in Kelvin. Black-body radiation tends to be full spectrum but will shift up or down depending on the temperature.
Some typical color temperatures:
1,850K – Candle Flame
2,500-2,800K – Incandescent bulbs
2,800-3,200K – Halogen bulbs
5,500 – 6,500 – Daylight (noon)
Fluorescent and LED lights:
Since fluorescents and LEDs produce white light using phosphors, they tend not to have full spectrums but rather several spikes that are perceived by most as full spectrum white light. These types of lights can also have spikes in colors that are not related to color temperature (color temperature adjustments typically deal with amber – blue adjustments) such the greenish tints that many inexpensive fluorescents have. This can make it more difficult to get good color balance with these types of light. Having said this, color corrected fluorescents and LEDs are getting better.
So what does this all mean? Most of the times you want to light a scene with all the lights having the same color temperature. While the pros will use gels etc. to get all of the light sources in a scene to have the same color value it is usually easier to just use the same type of light (at least the same color temperature) to light everything in the scene.
All the lighting is the same color temperature; now what?
If you are using a digital camera (back in the day, you had to use different film for different color temps), you should be able to use the “White Balance” function to get the proper colors. To do a white balance, set up the lighting and point the camera at a white object (a white balance card is the best but anything white can be used) and tell the camera to do a white balance. The camera will then analyze the image assuming that it should be white. It will then adjust the red, green or blue values so that they are in balance (for white or grey colors the rgb values should all be equal). The camera will continue to use these adjusted values until you do another white balance. As long as your lighting stays the same, the white balance should stay the same. If you change the lighting, then do another white balance.
Why not use Auto White Balance? When a digital camera is using auto WB, it is constantly analyzing the image and trying to guess at white is supposed to be. Sometimes it’s right and sometimes not so right. If at all practical, I prefer to do a manual white balance every time the lighting changes.
The image above is an example of mixed lighting. Half of the scene is lit by indoor lights and half of the scene is daylight lit. Notice the color of the white wedding dress and the white table cloths (in the back). This image is color balanced for daylight. The table cloths look white and the dress looks yellow. If the image was balanced for the indoor light, the dress would look white and table cloths would look blue.
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