Document image scanner with variable resolution windows

摘要

A document image scanner for reading a scanned document multiple times at resolutions different from the scanned resolution without rescanning. A sensor scans the source document to generate a digitized image that is stored in a memory at a first resolution. An input shifter is coupled to the memory for receiving a first number of pixels per line of the digitized image from memory. A vertical scaling element is coupled to the memory for changing a first vertical resolution to a second vertical resolution as the digitized image is transferred to the input shifter from memory. An output shifter is coupled to the input shifter for receiving a second number of pixels per line of the digitized image from the input shifter, wherein the ratio of the second number to the first number is the scaling factor. A horizontal scaling element is coupled to the memory for changing a first horizontal resolution to a second horizontal resolution as the digitized image is transferred to the output shifter from the input shifter. The horizontal scaling element causes the output shifter to receive the second number of pixels per line. An edge retention element is coupled to the horizontal and/or vertical scaling elements and to the input shifter for preserving an edge transition between pixels as they are transferred to the output shifter when the second resolution is less than the first resolution. The document further comprises a windowing element coupled to the vertical scaling element for selecting a portion of the digitized image to be transferred to the input shifter.