Superimposing Dynamic Range
We present a simple and low-cost method of viewing static HDR content based on reflective image modulation. We project images onto hardcopies, such as photographs, X-ray prints, or electronic paper (ePaper) so as to boost contrast, perceivable tonal resolution, and color space values beyond the potential of either hardcopies (when viewed under environment light) or projectors (when projecting onto regular screens) alone. We do not intend to compete with interactive HDR displays, but rather offer an 'everybody can do' alternative for domains that operate with static image content, such as radiology and other medical fields, or astronomy. Yet, electronic paper will allows for interactive visualizations.
In our experiments, we achieved contrast ratios of over 45,000:1 with a peak luminance of more than 2,750 cd/m^2, could technically re-produce more than 620 perceptually distinguishable tonal values (approximately 85% of all theoretically possible JND steps). Furthermore, we attained color space extensions of up to factor 1.4 (compared to regular projections) or factor 3.3 (compared to regular hardcopy prints). Thereby, the hardcopy resolution can be several thousand DPI or several hundred LPI, while luminance and chrominance are modulated with a registration error of less than 0.3 mm. Thus, compared with most existing interactive HDR displays, we support near distance viewing at a contrast frequency of up to 7 cpd (given our current registration precision and assuming a viewing distance of 50 cm).
We have presented our prototype together with medical datasets (one thorax CR scan, and one thorax CT scan with four different density settings and cutting planes - all monochrome) that were visualized with our luminance quantization technique to ten professional radiologists. They were all employed by different institutions, and were questioned independently from each other. With their experience, we asked them to compare the image quality of our approach to the image quality of X-ray film / laser film and high contrast medical monitors. As it is shown in the figure below, the subjective impression of the professionals was that our approach performs significantly better in all categories (contrast, brightness, number of perceivable tonal values, and spatial image resolution).