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Author Topic: Color Temperature  (Read 4752 times)
cowboy
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« on: December 18, 2007, 12:21:47 PM »
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This may seem a little strange but... I noticed that the temperature scale in CS3 Camera Raw decreases as the temp slider is moved toward blue. I thought the scale was calibrated in degrees K or some variation thereof. After thinking about it, Kelvin is a measure of black body radiation that goes from the lowest temp and the color red to the highest temperature of over 16000 degrees blue. This squares with what I observe with torches and gas stoves. The hotest part of the flame being blue.
So what is going on here? What is the scale in Camera Raw indicating?
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Graeme Nattress
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« Reply #1 on: December 18, 2007, 03:40:23 PM »
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The slider indicates what you think the colour temperature of the light used to shoot the image was, not what you want it to be. That's because the output white of the chosen colour space is fixed, probably D65 or D50 depending on choice.

Graeme
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cowboy
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« Reply #2 on: December 18, 2007, 03:58:50 PM »
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The slider indicates what you think the colour temperature of the light used to shoot the image was, not what you want it to be. That's because the output white of the chosen colour space is fixed, probably D65 or D50 depending on choice.

Graeme
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cowboy
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« Reply #3 on: December 18, 2007, 04:06:46 PM »
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Let me see if I have this straight. The temp shot was 4000 as the slider is moved  the scale is not registering the temp of what I am adding, but is what is needed to bring the white balance to say D50 or D60 which would be a cooler color  but higher in temperature on the Kelvin scale. The temp. scale in CS3  never shows the temp of the color added. By jove, I think I have it.
Thank you Graeme.
Bill
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Graeme Nattress
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« Reply #4 on: December 18, 2007, 07:22:52 PM »
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It took a lot of work for me to figure the code for this out. It's non-trivial :-) That said, it's a good moment when it finally works properly.

Graeme
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cowboy
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« Reply #5 on: December 18, 2007, 09:30:35 PM »
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It took a lot of work for me to figure the code for this out. It's non-trivial :-) That said, it's a good moment when it finally works properly.

Graeme
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I second that Graeme! Thanks again.
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Panopeeper
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« Reply #6 on: December 18, 2007, 09:41:15 PM »
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Another approach.

Imagine shooting a white object. If the light is reddish (low temperature), then the object appears reddish, it has to be shiftet towards blue in order to become white.

Now, if you shoot a white object in higher temperature but you say ACR that the light was reddish, then it shifts the color towards blue, and that, what appeared originally white, now appears blueish.
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Gabor
cowboy
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« Reply #7 on: December 19, 2007, 09:47:12 AM »
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Simply said panopeeper. Thank you.
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