White balance, Color temperature and Adobe Camera Raw.

H
Posted By
Hermie
Jun 6, 2004
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492
Replies
3
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Closed
Most light sources will not be 100% pure white but have a certain "color temperature", expressed in Kelvin.

"Color temperature" can be defined as the spectrum that would be emitted by a "black body" which is heated up to the corresponding temperature. This is easy to understand if you remember that a heated piece of metal will glow for instance. When heated up the color goes from red to yellow, to white, to blue.

The temperature scale makes things a bit counterintuitive because what we call "warmer" (red/yellow) light corresponds to lower Kelvin temperatures, while "cooler" (blue) light corresponds to higher Kelvin temperatures.

Next my question:
When you open a file in Adobe Camera Raw, the temperature slider works the other way around. When you move the slider to the left, the color temperature in Kelvin decreases and the white balance becomes more blue. When you move the slider to the right the color temperature increases and the white balance becomes more yellow.

Could someone please explain this reversed behavior?

Thanks in advance.

Herman

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J
john
Jun 6, 2004
In article <40c368d6$0$88385$>, "Hermie" wrote:

"Color temperature" can be defined as the spectrum that would be emitted by a "black body" which is heated up to the corresponding temperature. […]

Materials give off different wavelengths at different temperatures so the "Black Body" was invented and it is, of course, an abstraction (a hole, FAPP) intended to obviate arguments regarding body temperature neccessary to reach a certain spectrum. so that it can speak to _just_ the spectrum.
CC
Chris Cox
Jun 7, 2004
You are compensating for a light of a given temperature (to neutralize), not lighting the scene with a light of a given temperature.

Chris

In article <40c368d6$0$88385$>, Hermie
wrote:

Most light sources will not be 100% pure white but have a certain "color temperature", expressed in Kelvin.
"Color temperature" can be defined as the spectrum that would be emitted by a "black body" which is heated up to the corresponding temperature. This is easy to understand if you remember that a heated piece of metal will glow for instance. When heated up the color goes from red to yellow, to white, to blue.
The temperature scale makes things a bit counterintuitive because what we call "warmer" (red/yellow) light corresponds to lower Kelvin temperatures, while "cooler" (blue) light corresponds to higher Kelvin temperatures.

Next my question:
When you open a file in Adobe Camera Raw, the temperature slider works the other way around. When you move the slider to the left, the color temperature in Kelvin decreases and the white balance becomes more blue. When you move the slider to the right the color temperature increases and the white balance becomes more yellow.

Could someone please explain this reversed behavior?

Thanks in advance.

Herman
N
nomail
Jun 7, 2004
Hermie wrote:

Most light sources will not be 100% pure white but have a certain "color temperature", expressed in Kelvin.
"Color temperature" can be defined as the spectrum that would be emitted by a "black body" which is heated up to the corresponding temperature. This is easy to understand if you remember that a heated piece of metal will glow for instance. When heated up the color goes from red to yellow, to white, to blue.
The temperature scale makes things a bit counterintuitive because what we call "warmer" (red/yellow) light corresponds to lower Kelvin temperatures, while "cooler" (blue) light corresponds to higher Kelvin temperatures.

Next my question:
When you open a file in Adobe Camera Raw, the temperature slider works the other way around. When you move the slider to the left, the color temperature in Kelvin decreases and the white balance becomes more blue. When you move the slider to the right the color temperature increases and the white balance becomes more yellow.

Could someone please explain this reversed behavior?

What you are doing is setting the white balance, based on the color temperature of the scene. If the scene is too blue, you must set the white balance to a high value, to match that blue (high color temp) light. As a result, the picture becomes less blue (warmer), because you are setting the white balance (read: you are correcting) for high color temperature light.


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