In a raster scanning printer, a laser beam is scanned across a photoreceptor in a direction perpendicular to the photoreceptor motion. When there is vibratory motion of the photoreceptor or wobble in the polygon mirror, the raster lines on the photoreceptor will not be evenly spaced. We analyze the positioning error and show that fractional raster spacing error is equal to photoreceptor fractional velocity error. These raster position errors can result in various print defects, of which halftone banding is the dominant defect. The dependences of halftone banding are examined using a first-order geometry-based printing model, an exposure model, and a more sophisticated laser imaging model coupled with a xerography model. The system model is used to calculate print reflectance modulation due to vibrations in both charged-area and discharged-area development modes using insulative or conductive development. System parameters examined are halftone frequency, raster frequency, average reflectance, vibration frequency, and multiple-beam interlace spacing.

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Fast track article for IS&T International Symposium on Electronic Imaging 2020: Computational Imaging proceedings.

The expanding sphere algorithm computes an alpha shape tetrahedralization of a point set. Starting with a seed tetrahedron, the circumscribing sphere is squeezed through each face until it either touches another point or exceeds a preset radius. If no point is found, that face of the tetrahedron is part of the surface of an object. If a point is found, a new tetrahedron is constructed. This process is iterated until all the faces of the tetrahedra have been processed and no more connected points can be found. If there are points left over, the process is iterated, creating additional objects. The algorithm generates a list of objects, with an alpha shape tetrahedralization and a surface triangulation for each. Any points that cannot be made part of a valid tetrahedron are also returned in the extra points list. The algorithm is efficient for uniformly distributed point sets, with a running time that is linear in the number of points for such sets. Since the operations are local, it is also robust.