An efficient method and system for eliminating halftone screens from
scanned documents while preserving the quality and sharpness of text and
line-art is disclosed. The method and system utilizes one or more
independent channels with different sensitivities (e.g., Max, High, and
Low) to provide high quality frequency and magnitude estimation. The most
sensitive channel (Max) derives the frequency estimate, and the remaining
channels (e.g., High and Low) are combined to create the screen
magnitude. The Max channel is the most sensitive and will usually report
the existence of frequencies even when the screen is very weak.
Therefore, the screen frequency must be additionally qualified by the
screen magnitude. The screen magnitude can be interpreted as the level of
confidence that the local neighborhood represents half-toned data.