Tuesday, November 27, 2012
Full Dynamic Range Photography
How to capture the range of tones, from dark shadows to bright highlights, with traditional filters and HDR software
Over the past few years with the advent of simplified, robust and speedier high dynamic range (HDR) software, not to mention the implementation of graduated neutral-density filters (also known as graduated filters or grad NDs) in Photoshop's Adobe Camera Raw (the converter used for RAW image processing), Lightroom and other plug-ins and software, I've found myself using the grad NDs in my camera bag less and less. I wondered if I was getting lazy in the field, or if these new digital options were providing more control and better results. So, I decided to put it to the test to see if there was still a need for on-lens, in-camera grad NDs.
Understanding Grad ND Filters
Clear on the bottom and dark on the top, graduated or split neutral-density filters were originally designed for a specific purpose, a critical task physically impossible to recreate by any photographer no matter how amazingly talented he or she was. To stretch the ability of film or the digital image sensor to handle the dynamic range, the contrast from highlights to shadows is measured in stops of light in a given setting (as seen in Fig. 1, using a two-stop grad ND). The difference between grad and split NDs is the line of delineation from neutral density to clear, the grad ND changing smoothly over a longer section of the filter whereas the split ND transitions immediately.
Grad or split NDs can be used in a variety of situations, in color or black-and-white scenes, even upside down, yet their main design is to darken a bright sky, preventing overexposure while maintaining detail in the lower half of the frame, often a less illuminated landscape or cityscape area. A specific dodging (with the clear section of the filter) and burning (with the neutral-density section) is what's effectively happening when the filter is applied. They're mostly used with wide-angle lenses roughly no wider than 18mm and no longer than 35mm for two reasons: 1) the top and bottom of the filter needs to be seen to be effective, and a wide-angle's coverage provides this (as seen in Fig. 2, using a 24mm lens); 2) any wider than a 18mm lens and you risk vignetting from the filter or filter holder. As you stretch past a 35mm lens, maybe from 50mm to 80mm, a split ND can be used since the line of delineation is blurred by the longer lens, but after 80mm, only part of the filter is seen, and it becomes less, if at all, effective.
The ability to recreate a grad ND layer in previous versions of Photoshop was possible by applying a gradient, but it was less effective, time-consuming and a bit more complicated. When Adobe introduced the Graduated Filter tool in CS4, located in Adobe Camera Raw, also included in Lightroom 2, it was a wonderful addition for outdoor photographers. Two Photoshop versions later up to CS6, and the filter has improved. When used in combination with the Highlight, Shadows, Whites and Blacks sliders in ACR, the results are incredibly accurate and the tones are recovered well, giving the photographer great control over the final detail and look. Working with digital images in ACR and Lightroom, nondestructive workflow is also applied, so if you review the image a day, month or year later and want to change it, the unaltered RAW file is still available with the changes embedded, but reversible. With an on-camera filter, that just isn't possible.
One of the digital benefits with ACR are the sliders that control contrast, highlights, shadows, clarity and saturation, as well as sharpness and even color. Similar to colored grad ND filters, you can apply any hue to your filter in ACR—to any degree of saturation and intensity. I'm not much for enhanced color since I prefer more realism, but the option is nice to have when you may have lost some of the original color in the exposure. In Figs. 3a, 3b, 3c, 3d and 3e, a scene captured no less with a 200mm lens, you can see the options—3a, with no applied ACR grad ND; 3b, with a two-stop ACR grad ND; 3c, also with a two-stop ACR grad ND-compacted ND gradation and 3d, with a colored ACR grad ND. Fig. 3e is the final two-stop ACR grad ND version.
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