Wednesday, January 28, 2009

HDR

Master high dynamic range imaging to enhance tonal range or create hyperrealistic effects

This Article Features Photo Zoom

hdr
Late on an overcast day in Paris, I was able to capture three shots in a quick AEB burst at +/-2 with the Canon EOS 5D to cover the entire tonal range of this low-altitude aerial view, overcoming the effects
of aerial perspective by employing the HDR workflow.
High dynamic range (HDR) imaging is one of the most exciting and inspiring (and misunderstood and maligned) recent technological developments in digital photography. At its simplest, HDR is nothing more than a series of field and postproduction techniques to increase the overall range of luminance values captured and reproduced in a scene. HDR imaging techniques can eradicate clipping, minimize noise and pull up exceptional detail and color throughout an increased luminance range. Depending on your vision, the HDR process can produce subtle and photorealistic results or extreme surrealistic images that blur the line between “photo” and “graphic.”

MORE THAN A TRENDY LOOK
The runaway popularity of the extremely detailed, hypersaturated, illustration-style imagery has led many a photographer to dismiss HDR as nothing more than a party trick or a passing toning and tinting trend when this couldn’t be further from the truth! HDR imaging is a major player in the future of photography. The trendy, ultra-detailed aesthetic is simply one early evolutionary branch that has gained a lot of momentum. And when done properly, the same series of captured images can create photorealistic or surreal results. At its core, HDR is simply a way to give the creative photographer more high-quality data. How it’s processed is up to you.

A big part of the reason the over-the-top style is so prevalent among HDR beginners is the same old “fix it in post” mind-set that says a quick three-shot bracket at +/-1 is good enough in the field. HDR software programs can boost details and crank up local contrast, even in a single RAW, TIFF or JPEG—but it’s rare that such a tightly clustered bracket of one stop over and under will be sufficient to really reap the benefits that HDR offers to the still photographer. HDR software can overcompensate for underbracketing, and that’s often what leads to that typical over-the-top cartoon feel of final images that you’re likely to see on the popular photo-sharing sites such as Flickr.

To make the most of HDR imaging, you have to unlearn a number of things you may think are essential to the photographic experience. HDR often is described as being more like human vision than traditional photography, so let’s look at HDR with a fresh set of eyes.

TAKE SOME BAD EXPOSURES!
Bigger bit space means more legroom for highlights and shadows—so start by shooting lots of clipped images! Unlike single-shot still photography, where you’re looking for the one perfect exposure, with HDR, you want a number of different exposures. The goal is to capture the entire tonal range of the image to wind up with a sequence of frames capturing every brightness value in the scene before you. You want a series of overlapping exposures that ranges from white-clipped with overexposed shadows to black-clipped with underexposed highlights.

Depending on the particulars of your chosen framing and your exposure-value spacing, this may take three frames, five frames or more. There’s no formula that will work in every instance. You have to meter the darkest shadows and brightest highlights and determine the difference in exposures, and then come up with a bracketing sequence that covers this exposure range. If your camera’s automatic-exposure bracketing settings can span the exposure range, it’s a simple matter of firing the shutter button to let the camera burst the shots. If you must manually change the shutter speed, do so in even increments. Don’t go a 2⁄3-stop, jump to two full stops and then back to a 1⁄3-stop, if only not to confuse yourself in postprocessing!

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