Why do higher white balance Kelvin values make photos look warmer, even though hotter light is bluer?
Asked 12/25/2016
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I understand that a black body glows red/orange at lower temperatures and becomes white/blue at higher temperatures, so lower color temperatures are redder and higher color temperatures are bluer.
What confuses me is white balance in cameras and editing software: when I increase the Kelvin setting, the image usually looks warmer/oranger, and when I lower it, the image looks cooler/bluer.
Why does the white balance control seem reversed from the actual color of the light source?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
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The Why Different is just a difference between physics and art. The "temperature" simply is the actual color of black bodies when heated high (Like steel in a furnace). They do first glow red, and much higher temp turns white or blue. Just does, in physics. And the color does represent temperature.
But the art world has reversed notions, because mere humans seem to perceive red and orange colors (fire) as warm, and blue colors (ice) as cold. The red hot metal is an unusual situation, rarely actually encountered day to day.
Not sure which slider you see, but generally, the color from incandescent light is orange (maybe 3000K), or the open shade sky light is blue (maybe 8000K). The direct Sun is more 5000K-5500K, which we call white. That's physics. Then the temperature slider in photography is correction in the opposite direction, seeking white balance. More orange warms blue, more blue cools orange (which is the human perception of Art). The slider is often about correction of color, instead of about measurement of color.
What is interesting to me about White Balance is that our WB tools (Adobe) match the Lab color space axis. The WB Tint slider is just the Lab -a to +a axis, and the WB Temperature slider is just the Lab -b to +b axis. Center of both is the neutral color, no color cast. The Lab color L axis is Lightness, or brightness, which in Lab, is isolated from color.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
9y ago
0
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Because the white balance setting is a correction, not a simulation of the light source.
In physics, lower color temperatures are red/orange and higher color temperatures are white/blue. That part is correct.
But a camera’s Kelvin slider tells the camera what color the existing light is, so the camera can compensate and make neutral subjects look neutral. If the light is very blue (high Kelvin, such as open shade), the camera adds the opposite bias—warmer/orange—to balance it. If the light is very orange (low Kelvin, such as incandescent light), the camera adds a cooler/blue correction.
So increasing the white balance Kelvin value does not make the actual light bluer or hotter; it tells the camera, “the scene is lit by bluer, higher-temperature light,” and the camera responds by warming the image. Lowering the Kelvin value tells it the light is warmer/oranger, so it cools the image.
The “warm” and “cool” naming also comes partly from human perception and art: we associate reds/oranges with warmth and blues with cold, even though blackbody physics runs the other way at higher temperatures.
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