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Tuesday, September 15, 2009

HDR To The Rescue

High dynamic range saves the day in high-contrast situations

Labels: Quick FixHow To

This Article Features Photo Zoom


1. Here are the three photographs that I took of the scene. One was taken using 0 exposure compensation—meaning that I took the image at the camera’s recommended exposure setting. Then I took two additional exposures, one at +2 EV and one at -2 EV exposure compensation settings. Covering that wide of an exposure range, I was sure to capture both the highlight (sky) and shadow (rock) details that I wanted to see in my final image.

The +/- bracketing technique that I used for my lighthouse image isn’t set in stone for all HDR images. Sometimes you need to take more individual exposures covering three stops over and three stops under the “correct” exposure, such as when you’re photographing in very high-contrast situations. At other times, when there isn’t a wide contrast range, only one-stop bracketing is needed. What you don’t want is too few exposures. In my exploration of HDR photography, I’ve taken up to nine exposures at 1⁄2-stop increments to capture all the detail in a scene.


Before tone mapping

Before levels adjustment
Speaking of taking the actual pictures, I suggest using a tripod and your camera’s self-timer or a cable release (and maybe even locking up the camera’s mirror) for a steady shot. That said, I’ve taken handheld HDR images with an image-stabilizing lens and my camera set on rapid-frame advance and automatic bracketing.

In addition, you must leave your aperture constant, which means shooting in the aperture-priority mode (like I do) or in manual mode.


Above is a look at both of these dialog panels. As you can see, there are many options that give you total control over your image. Entire books have been written about what to do in these panels, and there are several websites with detailed HDR info.
If you want to get serious about HDR photography and shoot in automatic exposure bracketing (AEB) mode, consider getting a camera with +/-3-stop bracketing capability as opposed to cameras that offer only +/-2-stop AEB. Of course, you can bracket manually, but it takes more time.

2.
We need to combine our exposures into what’s called a tone-mapped image—the final processed HDR image.

The top photo at right is my image before tone mapping—what you’ll see on your monitor when all the images are combined using your HDR software. It looks strange because all the tones can’t be displayed on a monitor (or in a print). That’s where tone mapping comes in.

When you tone-map a series of images, you have two major options: using Details Enhancer and Tone Compressor—both of which have names that describe what they do.

For now, my quick advice is to play—and I mean play—with the sliders to see the effect each has on an image. A quick tip: The more you boost the Strength, Color Saturation and Luminosity in the Details Enhancer, the more surreal your image will appear; reduce these settings for a more natural look.

3. I used a bit of Levels adjustment (reducing the exposure by moving the shadow slider to the right) to create the opening image. I did that because I felt that the HDR image looked a bit flat.

The image at right is before my Levels adjustment. Compare it to the final image on the opening page and the exposures that I combined to create the HDR image, and you can see how amazing this technique is!

I have one more tip: Have fun! HDR imaging can open your eyes to a new world of creative possibilities—believe it or not!

Rick Sammon has published 31 books, including Rick Sammon’s Digital Photography Secrets and Face to Face: Rick Sammon’s Complete Guide to Photographing People. Visit www.ricksammon.com for more information on Rick’s HDR workshops.

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