color temperature

[scatesmd]

Hi everyone,

The idea of the color temperature has been puzzling to me and I think I finally hit on why I don't understand it.

As the temperature is increased in the raw converter, the color becomes more red ("warmer" in appearance), more blue as the temperature is decreased ("colder").

Outside of photography, the wavelengths become shorter and more "blue" as the temperature increases and photons gain energy. For blackbody radiation, this is described by Wien's displacement law which says the wavelength peak is shorter with higher temperature.

It seems as if the raw converters are backwards with respect to the relation between temperature and dominant wavelength.

I found myself confused as I tried to set white balance manually, as I had it backwards compared to what the camera expected.

The other alternative is that I REALLY don't understand! Am I misinterpreting what the raw converter/white balance practice is?

Thanks, steve

 

[Lars]

Steve,

The idea is that you increase the temperature of the sensor sensitivity spectrum while the subject lighting is constant.

What you say is more intuitive (and I agree) is that when you increase temperature, the lighting temperature should increase, causing a bluer light.

However, if you change the in-camera setting for WB temperature, you will notice that it acts the same way - changing sensor spectrum temperature. Thus, the raw converters are designed to work the same way as cameras.

So the key is to keep in mind that you change the temp of the sensor (to match the lighting), not change the temp of the subject lighting.

 

[Jan Brittenson]

As the temperature is increased in the raw converter, the color becomes more red ("warmer" in appearance), more blue as the temperature is decreased ("colder").

That's because a hotter illuminant produces bluer light, so needs to be adjusted towards red in processing. The opposite goes for a colder illuminant. What you're dialing in is the temperature of the actual illuminant used, not a simulated effect of changing the illuminant.

 

[scatesmd]

Hi Jan and Lars,

I seems I was looking at this from the wrong point of reference. Your explanations make sense. I definitely misunderstood what I was being told by the RAW converter.

Thanks for your help,

steve