Adaptive filtering method and apparatus for descreening scanned halftoned image representations

摘要

An adaptive filtering method and apparatus for descreening a scanned halftoned image representation is disclosed. The apparatus includes an image input subsystem (18,20); a processing subsystem (16) for processing halftoned image data provided by the image input subsystem; and software/firmware means operative on the processing subsystem (16) for a) low-pass filtering a halftoned input pixel value provided by the image input subsystem to produce a low-pass filtered pixel value; b) notch-filtering the halftoned input pixel value to produce a notch-filtered pixel value; c) determining a local contrast value for the halftoned input pixel value; and d) producing a descreened output pixel value based on the low-pass filtered pixel value, the notch-filtered pixel value, or a combination of the low-pass filtered pixel value and the notch-filtered pixel value depending on the local contrast value.