GRC 101 Term Paper on HDR Imaging

What It Is

High Dynamic Range photography (HDR) is a type of composite photography that shows a more dynamic range of light (and dark) than a single- exposure photograph1. Photographers achieve HDR by capturing an image at various exposures and then merging the photographs together, achievable with software such as Photoshop’s Merge to HDR function, first introduced in PS CS2 (2005). In November 2011, the San Francisco based company Soviet Montage used the multiple- exposure principle on still photography for an HDR video, using the same split- beam technology used to film 3-D2. Both the still and moving methods aim to make images look more true to life.

How It Works

HDR does to light what filters do to color.  If three black and white photos taken through RGB filters make up a color photograph, x number of photos taken at different exposures make up an HDR photograph. To manipulate exposures, adjust the aperture settings of a digital camera to capture more or less light. The aperture refers to the diameter of the circle allowing light onto the image sensor, like the iris of an eyeball.  A smaller F-stop indicates a larger opening and more light; each stop represents a doubling of light.  Photographers can also manipulate the shutter speed and ISO, depending on the scene they’re shooting, to capture as much light information as they want.

HDR photograph using f stop 0, +2 and -2, photo credit Kentaro Crockett

HDR’s range makes it especially popular for nighttime cityscapes, where it can capture various light values accurately and separately.  Manual exposure control makes HDR especially friendly to landscapes, where the subject stays still enough for capture with a camera and tripod.  Shooting people in this method would throw photographers back to the Matthew Brady days, when subjects sat unsmiling for minutes on end. iPhones with iOS 4.1 software advance HDR with a toggle that captures low, medium and high exposure images with one click and merges them in- hand, a the technology adapted from two iPhone 3apps, True HDR and Pro HDR3. The iPhone function gives a nice pre- programmed solution to those without patience, but still has trouble capturing motion. It throws down a worthy gauntlet for cameras that are exclusively cameras.

HDR video uses a split beam and multiple cameras to capture anything in HDR. Soviet Montage achieved HDR effects with two Canon 5D Mark II’s, one overexposed, one underexposed, focused on a split mirror beam4.

The apparatus, which involves positioning a camera on an x plane and a y plane with a beam splitter 45 degrees between the two, uses the same technology as 3-D filming. In 3-D, two cameras capture differences in space; in HDR, the two capture differences in light. Editing software then merges the over and underexposed “film”.

What it means for graphic communication

Personally, HDR video fascinated me more than HDR still photography. Photographers have experimented with multiple exposures of the same image since the 1850’s, when Gustave le Gray spliced together the sky of a short exposure photograph with the landscape of a longer exposed one5.  HDR video really does capture light more accurately.  On blogs and message boards, many sought a similar effect on a single camera:  some solutions required cameras with superhigh fps rates and alternating exposures programmed to take differently exposed images in rapid succession6. Users have already produced time- lapse videos in stop- motion using this method, but the fps rate still falls short of the 24 fps industry standard.  Others suggested filming a scene and then manipulating the exposures ex post facto.  This kind of inorganic rendering feeds much HDR backlash. “Faux” HDR takes a single photograph, copies it, digitally manipulates the exposures and contrast, applies tone mapping, and merges the images together as you would a traditional HDR photograph. Wired calls such images “a candy-colored, Wizard of Oz nightmare that would have even Michael Jackson moonwalking in his grave.” 7 Their surreal look suits advertising particularly well.

The quality of an HDR photograph goes back to “fixed at the time of creation”: the more photographers can do to increase the accuracy of their pictures at the time of creation, the more realistic the photo. The main frustration of all photographers is still, “Why can’t my camera just take a picture the way my eye sees it?”.  HDR furthers the underlying goal of all still and moving imagery since its conception:  to capture with a camera what the eyes capture in the brain.  To make images more lifelike.

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