Friday, October 5, 2012

Correct White Balance

Another in my ongoing quest to stomp on conventional wisdom where it is wrong.

A canard one sees from time to time online and, I suppose, in camera clubs and other places where the amateur with a little knowledge congregates, is the idea of "correct" white balance. This generally means that white objects are rendered as white on the screen or print. This is a classic case of a technical detail that is easy to understand and, in this age of digital, easy to adjust. The amateur with a little knowledge loves these things, they are handy stand-ins for actual knowledge and understanding, like shutter speeds, EVs, and so on. Since they can see it and you cannot, they get to feel superior and correct you. They can easily edit a copy of your picture, and show you. It's one click in most photo editors.

White whites are not, however, "accurate" white balance. The normal reason white objects fail to render as white is because the light falling on them is colored. A white shirt in shade will be a bit blue. The same white shirt under incandescent lights will be a little yellowy orangeish. The camera sees and faithfully records this. The white balance settings in the camera will try to make some effort to work out the color of the ambient light and make white things look whiter, but this is a somewhat haphazard affair. White whites are not always even pleasing, or flattering, white balance. Getting the whites white is, at best, a reasonable starting point and at worst a purely arbitrary measurement that weenies can use to feel smart.

Our eyes and the massive amount of brain we devote to seeing don't really care. We see white objects as white, almost no matter what the ambient lighting is. We mentally subtract the blueish tones of shade, and the yellowy tones of incandescent light. We do this when we're looking at photographs as well, which is why the angry yammering about "incorrect white balance!" is so confusing the new neophyte. We literally have to train ourselves to see white balance in photographs.

In reality, white balance is simply an effect. It can no more be correct than contrast, saturation, or any of a number of other effects we can apply to an image. It can certainly be ugly, it can fail to support the image, it can be visually confusing. It certainly affects the way we feel when we see a photograph. Like contrast and saturation, when a set of images are presented as a collection of related frames, we should try to make the white balance more or less match image to image, to help support the coherency of the set as a set. We can make the white balance more blue or more yellow, to subtly alter the way the viewer feels when the view the image.

A photograph obviously taken in shade, with the white balance adjusted to render white things a pure white arguably looks a little off. Our visual cortex sees the shade and tries to subtract the blue, and then things are just all wrong. We expect a slight blue tone to the whites, and miss it when it is gone.

When someone tells you your white balance is incorrect, by all means take a look. If all the people look orange, they might have a point. Your white balance isn't wrong, but it is ugly. If, having taken the time to examine the colors, they are where you want them, the correct response is "go pound sand, weenie."

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