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Tuesday, November 8, 2011

Auto HDR, Quicker, Faster And Better?

New DSLRs with Auto HDR features can create high dynamic range images in just seconds, but are the results worth the convenience?

This Article Features Photo Zoom
As yet, no Auto HDR controls include the option to save the original exposure sequence as either JPEG or RAW files along with the merged HDR image file. And as with all JPEGs, you can't adjust white balance and other image quality parameters as you can with RAW files. Hopefully, future improvements to the Auto HDR mode will include those options and give you the ability to save the final HDR image as a 16-bit TIFF+JPEG pair. And, eventually, processing times will be shorter, as it now takes between five seconds (Nikon and Sony) and 20 seconds (Pentax) to process the HDR JPEG, preventing you from shooting other images in the interim.

Normal JPEG

HDR 2-Stop Range
In both examples on these pages, you can see the effect in the overall scene, as well as the blown-up detail. Note how much the shadows are opened up in the 5-stop Auto HDR images. The effect is too strong, and the photos look overly manipulated.

The Fastest Way To Get A Perfect JPEG?
The shortcomings found in the current versions of Auto HDR clearly aren't ideal if you want more control and the ability to make changes to the final HDR image long after the sequence is shot. Those controls include the ability to tweak contrast, white balance, color saturation and, in some cases, adjust local shadow and highlight details. In more advanced programs, one frame from the exposure series can be selected to freeze a moving subject in a scene, while a moving subject in an Auto HDR image usually appears as a multiple exposure or worse. On the other hand, photographers who don't want to spend time creating HDR images on a computer, but want the improved tonal range of an HDR image in a scene with little motion will hail the feature. The only other question is whether the Auto HDR mode is the highest-quality way to reproduce a high-contrast scene.

Other techniques are available, including using a graduated neutral-density filter to lower the brightness of sunlit clouds, snow and sand. You also can set your camera's dynamic range features to the highest settings, which in some cases provides similar results to postprocessing a single RAW file to maximize highlight and shadow details. All of those techniques are based on a single exposure and allow you to shoot both action and static scenes.

In my experiences with a variety of camera models, including the Nikon D5100, Pentax K-7, Sony A580 and Sony SLT-A35, I found that Auto HDR modes have the potential to create much higher-quality results in high-contrast scenes with little movement. This is mainly due to the fact that creating a true HDR image, whether manually or with the Auto HDR mode, requires shooting several images at a combined wider exposure range than is possible from a single exposure. Most DSLR camera sensors have an 8- to 10-stop exposure limit, while a typical high-contrast scene can contain 13 stops or more of useful information.

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