The Magic of HDR Imaging

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There's a new phenomenon sweeping internet photography circles: HDR imaging. It's a technique that produces pictures which look hyper-real, but which most people assume are fake -- the result of some arcane Photoshop trickery -- when they first see one. But even though Photoshop is involved in realizing the images' true potential, they're not fake per se -- this image of the Golden Gate bridge, for instance, contains no photographic information that wasn't actually in this scene when the picture was made:

-- and yet, obviously, this isn't a picture of the Golden Gate that could be made in a single exposure by a traditional camera. Because the trouble with traditional photography is exactly that it relies on a single exposure to record all the information in a scene -- all the shadows, highlights and midtones, which on any given day are so disparate from one another that not even your eye -- much less a camera -- can distinguish all their subtle gradations at once.

So in a simplified nutshell, here's how HDR works: if you aimed a regular camera at this Golden Gate scene, you could either expose for the sky, and wind up with big blustery clouds but a muddy dark bridge, or expose for the bridge and the water and have a white, blown-out sky. Instead, the photographer put his camera on a tripod and took several pictures, exposing for different parts of the scene, and then carefully married them together in post. (We're assuming in Photoshop, although I believe there are other tools out there now.) By the way, you can see a larger version of this shot and check out the rest of this photographer's Flickr photostream here.

More HDR magic to follow:

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As high-tech as HDR sounds, however, it's been around, conceptually at least, since the dawn of photography. Even Wikipedia agrees:

The idea of using several exposures to fix a too extreme range of luminosity was pioneered as early as the 1850's by Gustave LeGray to render seascapes showing both the sky and the sea. Such rendering was impossible at the time using standard techniques, the luminosity range being too extreme. Le Gray used one negative for the sky, and another one with a longer exposure for the sea, and combined the two in a single picture in positive.

Here's an early LeGray HDRI called The Great Wave:
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Notice how the foreground water and whitecaps are perfectly exposed, as are portions of the sky, which would've been much brighter in reality.

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Click on the photos to see larger versions of them, and explore their makers' Flickr photostreams.

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For more, check out Smashing Magazine.

November 17, 2008 - 6:29am
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