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Thursday, October 14, 2010

Hi-Tech Studio: HDR Software

High Dynamic Range is more powerful than ever before

This Article Features Photo Zoom

From starlight to high noon, the sophisticated biology of the human eye can work within an extended dynamic range. With the ability to adapt to changing light conditions at the same time that it’s able to work within a large dynamic range of approximately 24 ƒ-stops, the human eye is able to see in a dimly lit room at the same time that it’s able to see through a window in that room to the sunlight outside. That being said, humans aren’t able to see in the dark at the same time that they’re able to view objects in bright light. Your eyes automatically will adjust to either end of the spectrum, but you can’t see both concurrently. In many respects, cameras have the same problem. In scenes with even limited amounts of contrast, cameras can pick up detail in highlights, and they can see detail in shadows, but they can’t record them both at the same time. Meter for the bright areas, and not enough detail will be captured in the darker areas. Conversely, meter for the shadows, and the highlights will be blown out.

HDR aims to extend the capabilities of cameras by adding detail that’s impossible to capture in a single exposure. Just as in the analog darkroom, combining multiple exposures carefully aligned can provide a singular new image with, theoretically, three times the amount of information. For practical purposes, this means that one image taken for the highlights, one for the midtones and one for the shadows will combine for an image that’s properly exposed for all three.

Capturing High Dynamic Range

In respect to an image, dynamic range is the distance in luminance values between the lightest and darkest areas of a scene. Pure white lies at the maximum end of the scale, and near black, as close to no signal as possible, at the lower end. By metering exposures to either highlights or to shadows, you can capture an ideal dynamic range for each area. With a one-stop (or one EV exposure value) increase or decrease in an exposure, you can effectively double or halve the amount of light. Most digital cameras make the whole process even simpler by providing exposure bracketing with many models that also will let the user dictate how much of an exposure value difference you’d like, often starting at 1⁄3 or 1⁄2 steps.

First and foremost, in these situations a tripod is a must. Even the slightest movements can cause ghosting once you’ve sandwiched exposures. There will be enough problems in multiple exposures with moving subjects as it is without having to worry about proper alignment of images. Secondly, how subtle or how dramatic the results will be depends largely on the difference in exposure values between shots. To capture more subtle tonal values, set more subtle exposure value differences. To capture the optimum amount of information that you’ll need for a scene, meter to the shadows, midtones and highlights. In general, three shots exposed by a difference of two stops will provide most of the detail that you need. For higher-contrast scenes, more exposures may be necessary.

Software And Plug-Ins

At the same time that many newer cameras are offering in-camera HDR capabilities, software designed for the specific needs of high dynamic range is becoming more proficient and easier to use. While this undoubtedly will result in an even greater flood of overly manipulated images, it also will lead to workflows that incorporate high dynamic range as an integral part of the process.

Ever Imaging’s HDR Darkroom functions as RAW converter software, as well as an HDR program with support of 16-bit TIFF files and multiple compressed or RAW files. Three different tone-mapping engines are provided for achieving realistic images. The Local Tone Balancer keeps tones in an image equalized while enhancing detail in shadows and highlights. The Local Tone Enhancer engine is built to pull as much detail as possible from an image and can handle larger files of up to 50 MB. The Fast Tone Compressor is also provided for working quickly with larger image files, claiming workflow speeds of three to five times faster than other programs. List Price: $99.