At first blush, there doesn't seem to be any obvious connection between
temperature -- how warm or cold it is -- and
color. So why is it that we photographers so freely throw around the term
color temperature? Sounds like it must be something important, and in fact, it is.
The term itself comes to us from physics, and refers to
black-body radiation; essentially, as a black body is heated, it glows in a color specific to that temperature, which is always measured in degrees Kelvin (K). In practical terms, any source of light will radiate at a particular color temperature, producing a predictable color in the visible spectrum. The chart on the left illustrates some examples. Traditional incandescent lightbulbs radiate at around 3000K, which is why their color is markedly yellow-orange. Fluorescent lamps, and some modern cool-white lightbulbs will radiate at much higher temperatures, above 6000K, and so will have a more bluish color to them. This has always been important to us in photography, as most color films were designed to "see"and record light in a normal daylight range, which is typically between 5000 - 6000K, and if the sources of light illuminating our photos varied from that, it resulted in images that didn't look natural. You've probably seen pictures that were either very yellow, or unnaturally blue-green. That's why.
Of course, painters and photographers have always confused the issue by defining colors, or color-casts, as being "warm" or "cool". This is almost certainly because we looked at a glowing fire, felt its warmth, and recognized the color it gave to anything it illuminated as a "warm" glow. And yet, the actual color temperature is at the cooler end of the spectrum, as you can see from the chart above. And those very high temperatures, above 6000K, are decidedly "cool" in appearance.
With color film, we used filters over the lens to add a compensating color in order to produce images that looked natural and daylight-balanced, or at least made sure to use light sources that were daylight-balanced. Most electronic flash units were fairly well color-balanced, or slightly biased to the "cool" end of the spectrum, which could easily be further improved in the printing process. Digital cameras can control for a wide range of color environments with their built-in white balance pre-sets, or the ability to set a
custom white-balance for a particular shooting environment. (This was covered in my last blog post; take a look).
Like so much in photography, color can be a very subjective thing; what looks pleasing to one may look odd to some one else. But there are times when we need to work with objective, agreed-upon standards, too; and the best example of this is when we make shade-matching images for the dental lab. An understanding of color temperature, and control of the digital camera, is part of what makes it work successfully.
Are you getting good results with you color images, or still something of a challenge? Let's have a nice warm conversation.
Later amigos!
Dave
