Tuesday, August 31, 2010
Toolbox: HDR Magic
Exciting software solutions for maximizing dynamic range in your photography
One of the wonders of digital photography is that there’s always something new to experiment with. Even a process that originates to correct a problem can develop a life of its own to become a hot trend. Case in point: HDR. It all started when some clever people sought to overcome the limited dynamic range of digital imaging by combining exposure information from the darkest areas with info from the brightest. Soon enough, photographers had run with it, using it to perfect the highlights, midtones and shadows of a scene, or pushing the limits of HDR to produce a compelling style of imagery that hadn’t been seen before. Now the options available for fine-tuning dynamic range are more extensive than they have ever been.
Dynamic range is defined as the variation of differences in luminance between the pure black (darkest) and absolute white (lightest) areas in an image. Increasing dynamic range means making more details visible in shadow areas while simultaneously retaining details in the bright highlights. Dynamic range that’s deficient on either end is said to have blocked shadows, blown highlights or both.
Built-in HDR capture has become a popular feature of many cameras these days. It differs from the process we’re considering here, but it’s still plenty potent. In most cases, these cameras capture more than one image—each at a different exposure—and then blend them internally following a set of rules. Those of us with cameras that don’t automatically broaden dynamic range can follow a similar procedure manually to get equal or better results. We bracket the exposure and then merge all of the data from the image files using specialized software. When executed correctly, the image contains the shadow detail from the slightly overexposed images and the highlight detail from the slightly underexposed shots—plus all of the midtones. HDR doesn’t work well with every scene, but it really shines in those problem situations where it’s tough to get rich black and clean white tones. In other words, it’s most at home in the worst situations.
Most of this magic occurs behind the curtain and is applied to the image we see through a process called tone mapping. That’s when 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.
Consistent with Adobe’s penchant for thoroughness, 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. List Price: $699.
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