The Mysteries of White Balance

The Mysteries of White Balance

Even folks who say they understand white balance sometimes have to admit it doesn't always make a lot of sense. Ah, the mysteries of white balance.

Let's start with a definition of white balance that form a basis for our discussion of the topic.
White balance can be viewed as the process of removing unintended color casts caused by the light source. Outdoors, light changes dramatically from the warmer hues of sunrise and sunset to the cooler tones of mid-day and overcast skies. Except at the extremes, our eyes do a pretty good job of dealing with this color correction process automatically based on experience and contextual triggers. But a camera sensor only sees what it sees, and somehow has to be told how to compensate.

Back in the days of film, you selected a white balance by loading your camera with a different type of film. Broadly speaking, there were daylight balanced films for most outdoor use, and tungsten balanced films for indoors where incandescent bulbs provided the majority of the lighting. These days, film is all but gone as are incandescent lightbulbs. But the need to compensate for the light source remains. You probably know it best as that knob atop your camera and that slider in Lightroom or Camera Raw. The mystery is in knowing just what to do with these controls and what they mean.

The color of light is specifically referred to in terms of color temperature. And it's this framing as temperature that causes much of the confusion. Measured in degrees the same as temperature typically is, color temperature designates the temperature a "black body" object has to be heated to for it to glow the color of light in question. But while it would seem that heating something more would cause it to glow ever more red orange, the truth is the exact opposite. As with glowing charcoal embers, orange is actually a fairly cool temperature, at least in terms of things that glow from heating. Heat things up far enough, and they'll eventually glow blue white. Bluish white may remind you more of icebergs, but this is just part of how white balance can be confusing. Warmer is cooler, and cooler is warmer.

Don't believe me? Spend some time with your camera. You should find that "daylight" white balance is somewhere around 5200 degrees Kelvin, and "shade," where it feels much cooler, is way up at 8000 degrees.

If you want an image to appear warmer, as in "more orange," one option would be to add a warming filter in front of your lens. But that would be so old school. Today, you can achieve the same thing by adjusting the white balance. Doing this though can seem a bit confusing. When you adjust the white balance, you're telling your camera or software what the color temperature of the ambient light was. You are describing the problem lighting, not the solution to it. Your camera will then compensate to bring things back in line based on what you told it about the problem. So, to make an image appear warmer ("more orange," the way it would be with a warming filter) you do so by telling your camera or software that the ambient light was in fact cooler. It will then compensate by pushing things to look more orange. And remember that orange actually means lower temperature in terms of degrees Kelvin color temperature. Or whatever. It's mysterious. But it works. You can make your sunset shots look more vibrant by using cloudy white balance, even though things look bluer under cloudy skies. It works because your camera corrects things to add the warmth you were telling it was lacking.

In Lightroom, you'll find the same scale of degrees Kelvin, and if you shoot in raw, you can freely adjust it here just as if you had done so in camera. With raw, the white balance exists only as an instruction saved along side the raw data. Whether you set it in camera or in software after the fact, that instruction doesn't get applied to the image pixel data until converted to a format other than raw. When displayed onscreen, it gets applied on the fly as the image is rendered to your monitor.

One difference in Lightroom and most software though is that this degree scale is accompanied by a color scale with blue to the left and orange to the right. Even though higher temperatures are in fact bluer and lower ones more orange. Based both on the color queues on the slider, white balance in Lightroom can be understood in terms of effect. If you want an image to look more orange (warm) you can simply push the slider towards the warm end. Never mind the Kelvin degree numbers. And regardless of the markings, you can adjust white balance simply by looking at the results. If you move the slider the wrong way, you'll figure out soon enough, and push the slider the other direction.

In camera white balance will affect your results if you shoot jpeg since the camera is then in charge of the conversion from raw. And your white balance choice will impact the appearance of your camera LCD image previews. But for the most part, you can ignore what set in camera and deal with it visually in Lightroom.

When you stop and think about it, white balance is indeed somewhat mysterious and frankly downright backward. Thankfully, you can simply adjust it by sight when you convert from raw. Never mind all this degrees Kelvin stuff.

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