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Why Auto White Balance Isn’t Perfect

Another great article by James Duncan Davidson about auto white balance in digital cameras:

Oh, come on, surely you don’t mean that modern photographic technology hasn’t figured out how to set the white balance automatically for every situation.

Actually, that’s exactly what I’m saying. Sure, modern electronics do a pretty good job a fair amount of the time. But, there’s one thing that prevents auto white balance from doing a perfect job and that is that the data it works with is the light reflected from your subject. Unless the light source is in the scene, there’s no way for the camera’s electronics to know what the color the light used to illuminate a scene is.

He points out a couple tools for helping get white balance right: the WhiBal reference card from PictureFlow and the ExpoDisc from ExpoImaging. I considered buying an ExpoDisc a few months ago, but decided it was too fiddly for my taste. I’ve always thought a grey card would be a good idea, but they’re usually big and not particularly durable. The WhiBal Pocket is about the size of a business card, waterproof, scratchproof, and rugged. Mine should arrive in a few days.

One interesting thing I’ve noticed about auto white balance is that using Lightroom’s “Auto” setting can frequently improve photos that the camera’s own auto setting messed up. Of course, for shots that fit cleanly into one of the presets (Daylight, Cloudy, Tungsten, etc.), choosing the appropriate preset works great. But for less clear-cut situations–say, an existing-light shot indoors with diffuse sunlight coming in through a window–choosing Auto in Lightroom tends to get me pretty close. I’m not sure why this is. I suppose Lightroom’s algorithm is just more sophisticated than the one built in to the camera. Or maybe it’s just better tuned to my own taste.