An adaptive filtering method and apparatus for descreening a scanned
halftoned image representation is disclosed. The apparatus includes an
image input subsystem; a processing subsystem for processing halftoned
image data provided by the image input subsystem; and software/firmware
means operative on the processing subsystem 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.
