METHODS

Except where noted, all images were shot using a Nikon D200 Digital Single Lens Reflex (DSLR) camera, using either a Nikkor 17-55mm lens or a Micro Nikkor 105mm lens. Camera Control Pro software (Nikon) was used to emulate a cable release - but a dedicated cable release or self-timer can achieve the same end. We used Polaroid UV filters and a tripod, but no additional lighting in all but one test case. All images were shot using an automatic bracket sequence of 9 shots taken at 1.0 EV steps above and below the metered exposure, varying the shutter-speed. Images were saved to both Nikon's NEF format (a version of the RAW format) and high quality JPEG files, in sequence of underexposed, metered, and overexposed. Each set of 9 images was processed using Photomatix Pro (HDRSoft), Hydra 1.5 (Creaceed Software), FDRTools (AGS Technik) and Adobe Photoshop CS3, running under Mac OS X 10.5.3. Each HDR image was saved in a floating-point, high-dynamic range format, as either a Radiance file (.HDR) or OpenEXR (.EXR). The HDR images were then tonemapped using Photomatix Pro's Detail Enhancement mode, and FDRTools's Compressor mode. Selected images were also processed with Hydra and Photoshop for comparison purposes. The settings while using the Photomatix Detail Enhancement mode were: strength 100%; colour saturation to 50%; light smoothing set to 3 levels: very low, medium and very high. Settings used using the FDRTools Compressor mode were compression and contrast set to 10, and smoothing set to 5. Hydra's Local Adaptation mode produced images nearly or only slightly below Photomatix Pro in quality, but user interface and stability prevented significant testing, while Photoshop's Local Adaptation mode generated very high-quality tonemapping, at the expense of a more involved process.

After tonemapping, images were saved as TIFF files. Comparison images were generated by taking the two images to be compared (usually the metered exposure and the resulting tonemapped output), by loading the images into Photoshop, converting them to grayscale, and combining them in two layers in a single document. We then set the uppermost layer to the Difference layer mode. This results in a grayscale image where darker regions indicate areas of little change between documents, and lighter areas indicating more significant differences. In cases where the camera moved between shots, the image presented in the tonemapped TIFF file was shifted relative to the metered exposure. In those situations, the tonemapped image was manually aligned with the metered image, which leaves uncompared areas along the edges of the comparison image. These uncompared regions were left in the resulting figures to preserve the size relationship between the difference image and the original.