Don't blow out your highlights! These days you hear this admonition all the time. I suspect it's the result of the little blinky warnings all of our cameras now have. Personally, I can't stand the damned things. Blink! Blink! Blink! I'd rather destroy a photo due to overexposure than to ruin it from being distracted by flashing displays. I turn the blinkies off and generally use the histogram to keep track of highlights. However, I digress—that's not the point of this post.
Forget about the blinkies for now. This article is all about knowing which highlights to protect and which ones to forget about. We know that we aren't supposed to clip our highlights but it's less obvious how to choose those highlights carefully. Not all highlights are created equal. The dynamic range of the natural world is much vaster than that which we can reproduce with photography. We must pick our battles wisely. Improper choice of highlight exposure is a certain prescription for faulty exposure of the rest of the image.
Clipped highlights—it simply means that pictorial information of the brightest areas of your image are lost. They are gone, blown-out to solid white. It's about the worst thing you can do to an image. It's much better to lose details in your shadows than it is to blow them out in your highlights. Losing highlight detail is like turning on the lights in a dark room. It's jarring to a viewer and psychologically distressing. Fading (or clipping) to black is much more natural and organic.
It is therefore natural for us to try to hold onto the highlights of our images. But, if we try to calibrate our exposure and tone reproduction to hopelessly bright highlights we'll ruin out entire image. Try pointing your camera at the sun (better yet, don't) and make a photo and you'll see what I mean. The sun might indeed be properly exposed but the rest of the image will be underexposed—relegated to noisy, deep shadows. Specular highlights can have the same deleterious effect. Specular highlights—the glimmer off the chrome of an auto, the shimmer on a body of water, or the glare from ice and snow—are almost as bright as the sun. And they can throw off an exposure almost as badly.
With digital capture we must choose our battles carefully. Digital imaging has a limited dynamic range, about the same as color transparency film. It's quite a bit less capable of capturing wide ranges of tones than is color or black & white negative film. Analog image capture also has the advantage of degrading gracefully when its range is exceeded. This is not so with digital cameras. When highlights blow out digitally, they are ugly beyond repair.
So, let's explore this more. Next time we'll learn about how to avoid highlight blowout with better exposure techniques. After that we'll try to fix problems in our existing images. We have no time machine to go back to the place and time we made those precious images. Some images are worth triage. We'll show you how to save them.