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Tuesday, June 8, 2010

Gadget Bag: High Dynamic Range Software

Use digital technology to make your photographs more like human vision

This Article Features Photo Zoom

High Dynamic Range—even the words sound exciting. Dynamic range describes the breadth of differences in luminance between the darkest (pure black) and lightest (absolute white) areas in an image. Increasing dynamic range translates into making more details visible in shadow areas while simultaneously retaining details in the bright highlights. Dynamic range that suffers on either end is said to have blocked shadows, blown highlights or both.

Adobe Photoshop CS5 HDR Pro
Some cameras have an HDR or pseudo-HDR function built in. They stretch the limits by compensating for underexposed shadows or by capturing more than one image (each at a different exposure) and blending them internally following a set of rules. Those of us with cameras that don’t broaden dynamic range automatically can follow a similar procedure and get equal or better results. In a nutshell, we bracket the exposure and merge all of the data from the image files using specialized software. When executed perfectly, the resultant image contains the shadow detail from the slightly overexposed images and the highlight detail from the slightly underexposed shots—plus all of the midtones.

Tone Mapping. It sounds simple, and it is—sort of. It’s the process in which the colors of a 32-bit HDR image are mapped to an image with lower bit depth. HDR software merges the multiple image data into one 32-bit-per-channel-per-pixel image, but shrinks it back to a useable size that can be displayed on your monitor. Along the way, the dynamic range of the 32-bit image is compressed to fit into a 16- or 8-bit-per-channel image. The larger file provides more data for adjustment and manipulation while the smaller image file is more easily displayed and printed. If your software allows it, always save the 32-bit image so you can do additional editing of the full data set later.

There are several software applications that do the HDR heavy lifting for you, including the newly refreshed Adobe Photoshop CS5. One of the many exciting new features found in Photoshop CS5 is HDR Pro. Adobe has greatly enhanced the simple HDR function by adding extended controls, an enhanced dialog box and improved image processing. The processing rules (algorithms) have been refined and now provide more accurate alignment of source files. CS5 can automatically deghost the annoying double vision that can occur when subjects have moved during image capture—or you can designate one single source file that’s to be used as the reference point for deghosting. HDR Pro offers extended tone-mapping tools and adjustment controls, and allows users to save their favorite styles as presets for future application. You even can simulate the HDR effect by applying the new HDR Toning feature to a single image. Contact: www.adobe.com.


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