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Tuesday, July 30, 2013

Keeping It Real With HDR


How to use HDR software to maintain appropriate contrast, overcome the limitations of the sensor and bring out detail—without overdoing it!



This Article Features Photo Zoom

The key to creating an HDR image that brings the photograph closer to the reality that our eyes perceived is to maintain appropriate contrast and saturation. In the images on these pages, Glenn Randall created 32-bit files with Photoshop CS6 or Photomatix 4.2. He tonemapped in Lightroom 4. Above: Mount Sneffels in late September from County Road 7, San Juan Mountains, Colorado.

One of the most frequent questions I'm asked by students in my landscape photography workshops is, "How do I make my HDR photographs look more realistic?" To answer that question, we first need a clear understanding of the problem. Our eyes can see a range of light intensities, from brightest highlight to darkest shadow, of something like 10,000 to one. A print can only display a range of light intensities of about 50 to one. In that sense, it's impossible for a print to ever look completely "real." But it's possible to get close—close enough that a print evokes many of the same emotions in the viewer that the real scene evoked in the photographer.


Aspen grove on top of Stealey Mountain at sunset, near Owl Creek Pass, San Juan Mountains, Colorado.
My guide when preparing prints has always been what I saw rather than what my film or sensor captured. I was never satisfied with the limited dynamic range of my 4x5 film, for example, and carried a quiver of eight graduated neutral-density filters to try to capture shadow and highlight detail the way I saw it. When affordable film scanning became available, I began using Photoshop to further adjust shadow and highlight density. Digital capture was another step forward, but even the high-end Canon EOS 5D Mark III I'm using today still has less dynamic range than my eyes, which is why I use a variety of digital techniques, including HDR, to capture what I saw.

But how do you really know what you saw hours, days or weeks later? According to Mark Fairchild, Professor of Color & Imaging Sciences at Rochester Institute of Technology (RIT), people are notoriously bad at remembering colors. We can distinguish thousands of different colors if they're placed side by side, but can accurately remember less than 100. We can easily remember if the flowers were blue or red, for example, but quickly forget what shade of pink we saw in sunset clouds. To further muddy the waters, people tend to remember colors as more saturated than they actually were, according to Fairchild. In addition, we tend to substitute certain "memory colors" for common objects. For example, we remember yellow-green grass as more green than it actually was. Similarly, we tend to remember sky as pure blue when it actually wasn't. Your best guide to what you saw, therefore, is your original bracketed set of images.

Let's assume you've loaded a bracketed set of images into your favorite HDR software. As you begin to adjust the 32-bit file, compare the region you're working on to the frame from your bracketed set that's properly exposed for that region. If you're adjusting the portion of the image that contains flowers, for example, "properly exposed" may mean the frame in which the green foliage surrounding the flowers was rendered as a midtone. If you're adjusting a sunset sky, however, don't pick the frame in which the glowing clouds are midtone and everything else is black. As pretty as those clouds may be, they're underexposed. Glowing clouds are a highlight; they should be brighter than midtone. Midtone clouds will look unnaturally dark if placed in a landscape where the flowers beneath are also midtone.

Here are some key principles for making your HDR photos look realistic.

1) Keep saturation under control. Wildly oversaturated colors may catch your viewer's eye, but excessive color saturation looks unnatural and is a flimsy reed on which to hang the entire impact of your image.


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