Hillshading With Oriented Halftones

Hillshading renders a surface with a three-dimensional appearance using shades of gray. Although shades appear as continuous tones, they must undergo a halftoning process for use with most computer output devices. This process generally uses one pattern of black and white pixels for each shade of gray, while attempting to make patterns associated with black and white pixels as difficult to detect as possible. The method described in this paper adds aspect information to hillshaded maps with oriented halftones. Twelve orientations of clustered-dot ordered dithers represent 30° intervals of aspect. Additionally, dithering matches sixteen shades of gray associated with analytical hillshading, with each interval representing 16 of 256 shades of gray. This process allows pattern and gray tone representations of the surface simultaneously.

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