Digital Focus: All About Color Balance
Feature: Taking Pictures With Perfect Color Balance
A friend of mine just returned a new digital camera to the store. After using it for a few days, he'd found that it took pictures with a distinct color cast. He traded it in for another camera that he hoped would capture more accurate colors, and was disappointed that his new camera has more or less the same problem. He asked me: What on earth is going on here?
Unfortunately, a slight color bias in digital photos is nothing unusual. How many times have you reviewed your shots on the PC only to discover that there's a pronounced red or blue cast to many of your pictures? Most of the time, there's nothing physically wrong with the camera; the images were just saved using the wrong white point. This week, let's talk about how you can correct the white point to take pictures with more accurate colors.
A Question of Temperature
Why do some of your pictures end up with unexpected color casts? In a nutshell, it's usually a question of color temperature. Every light source has a unique color temperature, typically measured on the Kelvin scale. Light sources with low temperatures are called "warm," and tend to have a reddish glow. Light sources with higher temperatures have a blue cast and are considered "cool." Sound backwards? It is, really--it just so happens that scientists use opposite descriptions when referring to warm and cool light. (And who are we photographers to argue?) Don't ask why. It's one of those mysteries, like why the tin can was invented about 50 years before the first can opener was patented.
That said, we usually don't notice different color temperatures in real life because our brains do a good job of correcting the images we see. We see all light as white, and colors tend to look the same no matter what kind of light they're viewed under. Digital cameras are programmed to do the same thing: They try to correct for a multitude of color temperatures, so all your pictures come out looking right. The problem is that cameras aren't nearly as good at it as the human brain is.
Automatic White Balance
Almost all digital cameras are configured by default to automatically set the white balance. In this mode, the camera measures the light in the scene right before it takes the picture and tries to eliminate any color cast. While automatic white balancing is fine for snapshot photography, you might notice that it's inaccurate a surprising amount of the time.
In fact, in my experience, automatic white balance works well in less than half of all the pictures I take. That's because the camera has to make assumptions about how much white or gray is in each scene, and then change the white point accordingly. As an aside, the automatic white balance also slows you down, since it contributes to the shutter lag common in many digital cameras.
White Balance Presets
If you don't mind fiddling a bit with your camera settings, you'll find that white balance presets are often a better alternative. Check your digital camera's manual for how to change the white balance--there are usually a half dozen or so settings for a variety of lighting conditions, like daylight, sunset, incandescent, and candlelight. If you use these presets for the right situations, your white balance will be somewhat accurate. But you need to remember to reset the white balance every time the lighting changes, or the color balance will be way off the next time you take a picture.
Manual White Balance
The most powerful and most accurate kind of white balance control is manual white balance--if, of course, your digital camera offers this feature.
When you set the white balance manually, you tell the camera to measure the actual lighting by pointing the camera at a white card or sheet of paper before you start taking pictures. Just like with the presets, if you set the white balance manually, you need to remember to reset it when the lighting conditions change--or you'll have a real mess on your hands.
You can get a white or gray card (either will work) from most photography shops, or you can use an ordinary sheet of white printer paper. When you take the measurement, though, be careful to fill the frame with the white card, or the reading won't be accurate. Likewise, ask an assistant to angle the card so the actual light source (such as the sun or room lights) reflects off the card into the camera. If there is a brightly colored object nearby--like a bright red car, for instance--make sure it doesn't reflect onto the card and create a color cast while you're setting the white balance.
A few weeks ago I recommended The ExpoDisc, a cool little filter that snaps onto the front of some digital cameras to help set the white balance.
Change the Color Balance in the Computer
If you have a color cast in your photos, don't worry--all is not lost. You can always use your image editor to remove it. Try saving this picture to your hard drive and opening it with a photo editor. The photo was taken with automatic white balance in tricky overcast lighting.
If you're using Paint Shop Pro (as I am), choose Adjust, Color Balance, Automatic Color Balance and click OK. You'll see an immediate improvement. Here you can see the before-and-after color balance side by side in the same image.
Is this an ideal fix? No, for a few reasons. First, it can be hard to perfectly correct a bad color balance after the fact--you'll always get more accurate colors if you nail the color balance in the camera to begin with. Second, mucking with color balance on the PC can degrade the image quality slightly, especially if you're working with JPEG images that you will have to resave and, in the process, recompress. So while computer white balance correction is a nice convenience, save it for times when need to save a potentially great image and you simply couldn't fix the white balance on your camera before shooting it.