You’ve likely heard that auto settings like auto exposure and autofocus aren’t fail-proof. They’re strong features, no doubt, and most photographers take advantage of them at least some, if not all, of the time. But the key to success with auto-anything is to make it work for you; that is, to understand its limitations, and know when it’s not going to give you the best results.
If you’ve been a photographer for very long, you’ve likely run into the situation in which a very bright scene, a snowy landscape, for example, caused your camera’s auto exposure to significantly underexpose the shot, giving you murky gray snow instead of brilliant white. Likewise, a shot that was naturally dark, like a portrait of a black cat, might have been recorded too light, also resulting in unwanted gray or brown.
In both of these cases, the auto exposure was tricked by the scene’s overall light or dark tone, and attempted to compensate for this problem by doing exactly what it’s designed to do: choose an exposure that will average out the tones in the scene. For many photographs, auto exposure does a fine job of selecting a correct exposure, for scenes when average is correct. The trouble is when a situation is not average. In those cases, it’s up to you, the photographer, to make the necessary adjustments.
The exact same thing happens with your camera’s Auto White Balance, only in this case, the issue is not with light intensity, but with color.
The Color of Light
Not all light is the same; different types of light have different colors built-in to them. Daylight is basically white, while light from a sunrise or sunset has a red, orange, or pink cast to it (caused by the light being bent through deeper layers of atmosphere). Shade is usually a bit blue, as is snow, as both of these situations are receiving reflected blue light from the sky. Standard incandescent (tungsten) lightbulbs give off a strong yellow cast, while fluorescent lights, long the bane of photographers, can be anywhere from blue, to purple, to green.
Your camera needs to know the color of the light so that it can accurately record the rest of the colors in the scene. With film, this White Balance” is built into the product (i.e., Daylight film and Tungsten film), but with digital cameras, we have the ability to change the White Balance on the fly. If you shoot a room illuminated only by tungsten light with your camera’s Daylight White Balance setting, the resulting photo will show incorrect colors that are skewed towards yellow (try it and see for yourself). You could also shoot an outdoor natural-light photo with the tungsten setting and get some simply awful blue images. But when these situations are shot with the correct White Balance selected, the colors in the photos should be spot-on accurate.
The Auto White Balance Blues
Your camera likely offers a handful of White Balance choices, settings like: Daylight, Cloudy, Shade, Flash, Tungsten, and Fluorescent. There is also, surprise, an Auto choice.
Many beginning photographers tend to set their White Balance selection to Auto and leave it there. This mistake can be the cause of quite a few photographic problems. Like your auto exposure, Auto White Balance is pretty good. Especially when dealing with artificial light sources, the results of Auto can be very satisfactory. The trouble arises when a color cast is desirable, or when shooting a subject that is mostly one color.
A great example is a classic sunrise or sunset scene. In this case, there can be quite a lot of red or orange light illuminating the scene. If you choose Auto White Balance for this shot, the camera will evaluate the scene and think, “Hey, something’s wrong! There’s a lot of red here! Better back off on the reds.” The problem is, you do NOT want your camera to correct for those colors. In this case, having a lot of red in the scene is correct according to the subject and your intention. Auto White Balance will probably deliver a sunset that has a much more bluish feel, not as dramatic, and not what the scene actually looked like.
Another way Auto White Balance can be fooled is with objects that are mostly one color. A good example is flower photography. Suppose you’re photographing a large pink flower that fills the frame almost entirely. Auto White Balance will look at this shot and think, “Whoa, too much pink! Gotta back off on that.” Auto White Balance has no way of knowing if subject is truly that color, or if it’s the lighting. The only thing it can do is try to deliver what it perceives to be an average color balance for the image. In this case, the flower in the photo won’t appear the correct, vibrant pink that it was.
Auto White Balance can even cause slight inaccuracies to everyday outdoor photos, often resulting in shots with just a bit too much purple than they should have (the result of Auto trying to over-compensate for green vegetation).
So what’s the solution? Use those White Balance presets! Many photographers, including me, use the Daylight setting a great deal of the time, to help ensure accurate colors during all times of the day and in many weather conditions. The Shade and Flash presets can also be quite useful. If you’re shooting JPEG files, selecting the correct White Balance at the time of shooting is critical. But even if you shoot RAW files and have the (very useful) ability to adjust your White Balance in post-production, choosing the correct White Balance preset at the time of shooting can start your images off right, and save you plenty of time, and who doesn’t like that?
Do you have any other stories or examples where Auto White Balance did you wrong? Please share in the comment below.