Is it Real or Is It High Dynamic Range? How Software Is Changing the Way We Look at Photographs

11/6/09Follow @wroush

You know how listening to music on a friend’s pricey Bose headphones makes it harder to tolerate your tinny little speakers at home, or watching your favorite show on a high-definition screen spoils you for regular TV? I’m at a moment like that in the way I look at photographs. For the last few weeks, I’ve been playing around with a new computerized technique called high dynamic range (HDR) photography, which can lend a stunning level of brightness, contrast, and detail to digital images. And now every traditional non-HDR image that I see looks flat and dull by comparison.

It’s a dilemma, actually, because the HDR “look” can be peculiar, artificial, even surreal. If you lived in a world where every photograph was made this way, you’d have a constant migraine. But for now, I’m a little bit addicted to HDR. And at the risk of getting you addicted, too, I want to talk this week about how the technique works, what you can do with it, and how it can help all of us question some of the conventions and expectations we’ve built up around the art of photography, and around the related art of looking at photographs.

HDR images are unusual because they don’t represent a single moment in time, like most photos, but rather are digital fusions of several images of the same scene, taken at different exposure levels. (In photography, the longer the exposure time, the more light gets captured by a camera’s film or digital sensor, and the brighter the resulting image.) To collect raw material for an HDR image, photographers generally take at least three pictures: one that’s underexposed, one that’s overexposed, and one at a normal exposure. This is called exposure bracketing. The easiest way to explain is to do a bit of show-and-tell:

1. Normal Exposure

1. Normal Exposure

2. Underexposed

2. Underexposed

3. Overexposed

3. Overexposed

Digital cameras have come a long way in the last 10 years, but the sensors inside them are still nowhere near as good as the human eye at handling the huge variations in luminance that occur in the natural world. (Photographers call this variation dynamic range.) As you can see from Photo 1 above—the one taken at the standard exposure level that my camera chose automatically—the trees look okay, but the sky is pretty washed out. That’s because the camera, in choosing an exposure that would capture some detail in the hills and leaves, wound up gathering too much light from the much brighter sky above.

The HDR process offers a way to compensate for this technological limitation. If you examine the underexposed image (Photo 2) above, you’ll notice that the landscape is pretty dark, but there’s a lot more detail in the clouds—you can actually see how shapely they are. Conversely, in the overexposed image (Photo 3), the sky is a featureless white blur, but you can see a lot more stuff happening in the trees—detail that was largely lost in the shadows in the normal exposure.

Software for creating HDR images uses some fancy math to merge all three exposure-bracketed photos into a single image that preserves the detail from both the brightest areas of the underexposed image and the darkest areas of the overexposed image:

4. HDR Image

4. HDR Image

Pretty cool, huh? Of course, you wind up with an image that has far more dynamic range than photographic paper or standard LCD monitors are capable of conveying. So most HDR software also goes through a second step called “tone mapping,” which compresses the fused image into a final version that still has a high contrast ratio and color saturation, but also looks good when printed or displayed. (Let me forestall criticism from traditional film photographers right now by acknowledging that certain kinds of film have a very high dynamic range, and that good photographers can deal with huge luminance variations without resorting to software tricks. Just look at Ansel Adams.)

To make the images above, I simply snapped three pictures of the original subject—the foothills of the Green Mountains in Vermont—using the auto exposure bracketing setting on my camera. (The trick here is to hold your camera steady. It’s best to use a tripod.) Then I merged the photos on my Mac using Photomatix Pro, a $99 program made by a small company in France called HDRSoft. There are other standalone programs for making HDR images, including a few free ones, but Photomatix produces the best results, in my experience. If you’re lucky enough to own a recent version of Adobe Photoshop, it has a built-in function called “Merge to HDR” that does the same thing.

Since buying Photomatix, I’ve been going a bit wild with the HDR technique. You can see more of the results by checking out this photoset on Flickr or the slide show at the end of this story. And don’t stop with my images—I’m a rank amateur at this, and to appreciate the full possibilities of HDR photography you should also look at what photographers like Jared Earle are doing (I’m especially struck by this Earle image).

I have to warn you—most of these photos look strange. It’s not that they’re unrealistic, exactly; in point of fact, HDR images are much closer than normal photos to what the human eye can see in real life, given its amazing sensitivity to wide variations in luminance. It’s just that traditional technologies have trained us to expect something very different from a photographic reproduction. We aren’t used to seeing so much detail in both the foreground and the background of a reproduction, and in both the light and the dark areas.

It’s because of all this eye candy vying for your attention that some HDR images almost look staged, as if someone lit the scene with Klieg lights. HDR pictures sometimes remind me of wall calendars from the 1950s, or of the sparkling, saccharine worlds created by visually minded directors like Tim Burton or Bryan Fuller (Charlie and the Chocolate Factory, “Pushing Daisies”).

Now, whether HDR photos make good art is another question. A friend of mine, composer/photographer/author Graham Ramsay, feels that most HDR images look unreal, and that they assault the viewer with a confusion of detail. He’s an evangelist for the idea of intentionality in photography—the careful composition of an image, in both the shooting and the processing phases, in order to capture an emotion or tell a story. If every square inch of an image is equally busy with texture and variation, Graham argues, the viewer’s eye doesn’t know where to go; such pictures may convey a lot of information, but they don’t convey ideas. An HDR image, from this point of view, is no closer to art than a photograph snapped by a robotic probe on the surface of Mars.

Another professional photographer, Michael Reichmann, anticipated some of these criticisms back in 2005, when Adobe first added the “Merge to HDR” function to Photoshop. Reichmann called the feature “the holy grail of dynamic range,” since it allows photographers “to easily create images that were previously impossible, or at least very difficult to accomplish.” But like guns and nuclear power, he warned, photo-editing software “can be a force for evil as well as good,” and he predicted that many photographers would use the new feature to create “some really silly if not downright ugly images.”

HDR MatrixAnd perhaps that’s what I’ve done. I certainly wouldn’t argue that my HDR photos are great art. But I also think that our appetites and cravings as consumers of images can vary. Sometimes you just want to be enveloped in the artistic sensibilities of an individual photographer or photojournalist—an Alfred Stieglietz or an Ansel Adams or a Margaret Bourke-White or a Peter Menzel. And sometimes you may want to immerse yourself in an image where detail and fidelity, rather than emotion or storyline, are the intention. (I happen to be the kind of person who enjoys poring over the stunning images that the Sojourner, Spirit, and Opportunity rovers have sent back from Mars.)

In his essay on HDR, Reichmann allowed for the possibility that “in the hands of sensitive artists and competent craftsmen…we will start to be shown the world in new and exciting ways.” It may be a while yet before serious photographers figure out how to use the HDR technique to make their images more expressive. But already, the technology is forcing us to reassess what we mean when we say a photograph looks real; it’s exposing the fact that the kinds of photos we used to call realistic are actually attenuated versions of what our eyes really see. (You might even call conventional photos LDR, for low dynamic range.) HDR is just another tool in the toolbox—and of course it would be silly to use it too often. But for now, my camera is an HDR hammer, and everything is looking like a nail.

Update 3/20/10: I’ve come across two amazing new (to me) HDR websites: Trey Ratcliff’s Stuck in Customs and a spinoff community site,

Continue to Page 4 for a slide show of HDR images from around New England.

For a full list of my columns, check out the World Wide Wade Archive. You can also subscribe to the column via RSS or e-mail.

HDR Slide Show

(Click on the arrows below to advance)

photos will appear here, please wait…

Wade Roush is a contributing editor at Xconomy. Follow @wroush

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