“Color Temperature” and Color Bias

"Color Temperature" refers to (in photography & videography) the relative balance of Red and Blue in light.

"Color Temperature" can be thought of as a bias, or corruption, to the natural colors we expect to see in a scene that is photographed either with film or with digital equipment.

Color Temperature is measured in degrees Kelvin (°K), which are in magnitude (the amount of change between one degree and the next) the same as Celsius or Centigrade, except that degrees Kelvin start at −273.15°C (−459.67°F), which is "Absolute Zero" (the point at which all molecular activity is theorized to have ceased). Thus, Kelvin temperature is a metric that is much more common in scientific applications such as Color Science and Astrophysics than appliance repair.

Many things cause variance in Color Temperature. Let's just accept that a Color Temperature of 6504° is considered a standard illuminant*, and that low Kelvin Color Temperature produces a relatively Yellow or Butterscotch bias, and high Kelvin Color Temperature represents a relatively Blue color bias. Simply because photographers have for decades named everything as confusingly as possible, low Color Temperatures are described as producing "warm" color and high color temperatures are described as producing "cool" color.

This image is adjusted 2500°K too low, with no Green Compensation.

This image is adjusted 1500°K too high, with no Green Compensation.

This image shows the color temperature as corrected when shot using a professional digital camera.

However, we humans tend to interpret-or "accomodate"-some of what our (normal) eyes actually see to suit our expectations, and Color Temperature is one of the matters that we accomodate our cognition to. In fact, we can sense Color Temperature extremes with little coaxing, and can sense subtle Color Temperature changes in a variety of conditions. Our perception of Color Temperature also depends on a scene's total illumination as we are less capable of sensing color in relatively low light conditions.

Color Temperature is not the only visual phenomenon to which we accomodate our cognition.

Various illuminants such as flourescent or incandescent light bulbs produce light with inconsistent Color Temperatures. This can be problematic when trying to view photographic prints accurately or when testing vision. It can also be problematic when photographing scenes using those nonstandard illuminants or when viewing such imagery on a monitor that is not calibrated (and "profiled") to a reasonable level of accuracy.

Here's an example of the difference Color Temperature can make. I have to offer a Caveat concerning this demonstration-although produced in a forensically defensible manner the accuracy of the colors you see will depend a great deal on the performance of your monitor (as well as the normalcy of your own vision). If your monitor itself is not terribly accurate (an overwhelming majority of monitors are inaccurate until color managed) this demonstration will not be terribly reliable.

The image is a vertical aerial (an "orthograph") of a retail shopping facility shot well before dawn to demonstrate the footprint and intensity of the parking lot lights. Select a Color Temperature from the four "Radio Buttons" beneath the image to simulate the different natures of the same amount of luminance at varied Color Temperatures.**

So what?

In short, matters of Color Temperature (especially on non-color managed systems) can make it extremely difficult to tell if the car was Yellow or Light Green, or if the suspect's sweater was Aqua or Royal Blue. Arrests can be initiated based on profoundly faulty descriptions, and that's a problem that can graduate into a countersuit.

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*Color wonks will know that D65 is 6500° K, but 6500° K is not D65. They'll also know that when the word "Metamerism" does pop up in a post on this site the reader needs to prepare for a wild ride!

**This demonstration was prepared without Green Compensation, and (out of merciful kindness) without any reference to Haeberli Vectors.