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Tuesday, March 8, 2011

HDR Software Roundup And Review

The technology has matured beyond a gee-whiz bit of digital trickery into a full-fledged tool that nature photographers can use to overcome the limitations of the image sensor

This Article Features Photo Zoom

Longs Peak from Twin Sisters, Rocky Mountain National Park, Colorado.
HDR Efex Pro Deghosted Noise Reduction—Processed with Nik Software HDR Efex Pro’s Global-High ghost-reduction utility. Noise reduced in Adobe Camera Raw before HDR processing.

Interest in high-dynamic-range (HDR) imaging has exploded over the last few years. More than half a dozen HDR software packages are now available, and for good reason, as HDR imaging promises to solve one of the great challenges of photography: taking the broad range of tones we see in the real world and compressing them into the much narrower range of tones we can reproduce on a monitor or on paper.

Until recently, I was an HDR skeptic, however. All too often, HDR software produced unnatural results. Shadow contrast sometimes looked strangely flat. Colors shifted in odd ways, and dark objects set against bright backgrounds often developed pronounced halos—weird bright bands along the object’s edge.

Raw—Best image possible from a single raw capture, processed in Adobe Camera Raw.

HDR Expose—Processed with Unified Color Technologies HDR Expose.

HDR Photomatix Deghosted—Processed with HDRsoft Photomatix Pro 4.0’s Details Enhancer and the semi-manual deghosting utility.

Granted, HDR software must solve a tough problem: replicating the intricacies of human vision. Our visual system analyzes contrast locally rather than globally. In other words, we don’t look at the darkest part of the overall scene and call it black, then look at the brightest part and call it white. Instead, we analyze contrast within regions, most obviously shadows and highlights, but also more subtly. The challenge for HDR software is to maintain good local contrast within regions, while still creating believable transitions between regions. Simply taking the overall range of tones and compressing it in some linear fashion won’t cut it.

HDR Photomatix EF—Processed with HDRsoft Photomatix Pro 4.0 using Exposure Fusion.
The latest generation of HDR software goes a long way toward solving these problems. In my testing, three programs stood out. HDRsoft Photomatix Pro is best used as a stand-alone program or as an export plug-in for Lightroom; the plug-in versions lack some features. Nik Software HDR Efex Pro can be used as a plug-in for Lightroom, Aperture and Photoshop. Unified Color Technologies HDR Expose is a stand-alone program that also can be used as a plug-in for Aperture and Lightroom. Additionally, HDR Expose has a twin, a Photoshop plug-in called 32 Float.

The most difficult subjects for any HDR package are those that include the sun. Often, HDR software creates unnatural concentric bands around the sun, with sharp transitions between bands rather than a smooth gradient. For my first test case, I chose an image of the sun setting over Pigeon Peak, shot from the summit of Mount Eolus. For my second test case, I picked a high-contrast image of a stormy sunrise over Longs Peak. Using a Sekonic L-608 spot meter, I measured a six-stop range between the dark, shadowed midground evergreens and the glowing clouds. For each test scene, I made three exposures, with exposure compensation values of -2, 0 and +2.

HDR Photomatix TC—Processed with HDRsoft Photomatix Pro 4.0 using Tone Compressor.
To evaluate the results fairly, I needed a standard for comparison. The most useful, I decided, was to take the best single exposure from the bracketed set of exposures and create the best image possible using Adobe Camera Raw. My goal in using each HDR package was to create an image that had better highlight and shadow detail than I could extract from a single exposure, while still looking natural. All HDR software easily can create the wild, over-the-top, “HDR” look; the challenge is to create an image that resembles what we saw. I did no further processing in Photoshop on either the single RAW or the image output from the HDR package, since that would make valid comparisons impossible. All of the HDR packages were able to produce better detail in the highlights and shadows than I could achieve with a single raw file. Beyond that, the programs differed in many respects.


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