Scanning equipment for a low-cost facsimile machine which includes a variable gain amplifier and a comparator circuit for correcting nonuniformities in lighting, lenses, light sensors and the like. Each line of a document being scanned is subdivided into a number of picture elements that individually...http://www.google.se/patents/US4980778?utm_source=gb-gplus-sharePatent US4980778 - Method for correcting nonuniformities in pixel output level for a line scanner
