Abstract: An apparatus for scanning documents combines digitizing circuitry with a scanning platen to achieve precise selection of image areas on large documents. A vacuum system holds the document in place against a perforated scanning surface during registration and scanning. The assembly of scanning surface, vacuum chamber, and digitizing circuitry move as a unit beneath a fixed scanning apparatus. The apparatus further has a mechanical structure which allows the table assembly to rotate about a pivot axis toward an operator to reduce parallax error in mapping image areas.

Abstract: In digital halftone color printing, low spatial frequency patterning can occur due to the interaction of the overlapping angled halftone screens. The moire patterning can be minimized by automatically constructing digital haltone angled screens from screen tiles which are designed to minimize the low spatial frequency patterning. The screen tile boundaries are generated in response to selected integers which, together with the number of screen dots along a side of the tile in the direction of screen pitch measurement, determine the a limit on the magnitude of screen angle error. Based upon these values, each pixel within the tile boundary is associated with one of the screen dots of the image. Typically, the pixels are added to potential candidate lists from which they can be selected for inclusion within a particular screen dot.