Conceptual problem with the Temp slider in LR/ACR

Hello,

I am having a conceptual problem with the Temp slider in LR/ACR. When I move the slider left (toward the blue end) the image does indeed get bluer (cooler), and toward the other (yellow) end the image gets warmer. Good. But the numbers don't seem to correspond. If the numbers represent degrees Kelvin, as I thought, then redder tones should be smaller numbers, shouldn't they (you don't have to heat that theoretical "black body" to as high a temperature for red tones as you do to get blue tones)? For instance, normal daylight is around 5600K, sunrise/sunset about 3200K (the terms "warmer" and "cooler" seem to be contrary to this--but might be referring to the air temperature differences between day and night, say). So, if I want to move an image from normal daylight toward the warmer tones of sunrise/sunset, I thought I could just set the Temp slider to about 3200--the color temperature at sunrise/sunset--and the image would get warmer. What I get is a bluer image. It's odd, because I've been using these sliders for a while, and just noticed this. What am I missing?

Michael

I think the concept here is that you're trying to set the colour balance to produce a neutral white - so in "warmer" light you need to correct the image to be "cooler" than it would otherwise be to make it come out neutral overall. As to "warmer" vs "cooler" in terminology, I think that's referring to the psychological effect (red=warm, blue=cold) rather than the colour temperature.

...Mike

I agree with Mike. The color temperature slider is designed to be set at a value that matches the color temperature of the light source, so that whites in the image become neutral. This is why it operates in "reverse" from what you would expect if it were simply a color filter sort of slider.

All right, I think I'm actually getting this.... Let's say I shoot a picture in the early am, oh around 3200K (you know we might actually be able to tell time this way: "I slept in this morning; didn't get up until 4400K!" "Meet you at the mall at 6350K," well, maybe not). When I bring the image up in a viewer, it's going to be pretty orange, as that was the color of light at that time of day. If what I want is a neutral white (instead of an reddish white), I move the Temp sider until it indicates 3200, which tells LR/ACR the color temperature the image was shot at. LR/ACR then adjusts the image to try to give a neutral white (in this case, blues the image). In other words, I tell it it was shot at 3200K, and it tries to adjust the image to look as if it had been shot at 5500K. Of course, that defeats the point of getting up so damn early to catch that light in the first place.

Just think in terms of settings rather than corrections. If you shoot in daylight that is 5000 K, you have to set the WB to 5000 K to get a neutral image. If you set it at 6000 K, you set it to neutralise light that is more blue, so the resulting image will be more yellow. And vice versa. It's exacly the same as using a daylight film (meant for 5500 K) indoors (where light is 3500 K). The result is a strong yellow/orange cast because this film is neutral at higher color temp than the light really is.