ADAPTIVE OPTIMAL LINEAR FILTERING FOR 1-TO-N BIT HALFTONE DESCREENING
Original Publication Date: 1994-Feb-28
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
When processing a digital image it is desirable to have several bits of gray scale resolution per pixel. The processing may be any of a number of typical operations such as tone rendition modification, halftoning with a screen optimized for a particular process, edge sharpening, or resolution conversion. Often a document to be processed, such as a halftoned image, is available only in binary, one bit per pixel, form. Prior to processing, conversion to multibit quantization is currently being accomplished in Xerox@ scanners (e.g.,7650 Pro Imager) by using low-pass filtering techniques to remove the halftone screen and give an estimate of a multibit per pixel version of the original image. This type of filtering tends to blur edges and lose fine detail. One technique employs Logical Filtering and offers substantially better results than traditional low-pass filtering. The present disclosure describes an adaptive filtering technique for l-to-N bit conversion of halftone images that performs a more accurate reconstruction than low-pass filtering and is statistically optimal in a mean square sense for a collection of images.