Disclosed herein is an image processing method for producing enhanced
halftone edges, particularly suited to those edges which only lie upon
the background as apposed to those edges which abut other halftone
screens. It utilizes a step of defining border pixels and a step of
halftoning those border pixels in a different manner than the halftoning
applied to the interior region of the tint or image segment. The
preferred halftone for the border pixels will be related to the interior
halftone by some number of common spatial frequency harmonics. Examples
of common-harmonic screening for an edge include, but are not limited to:
(a) same screen with different tone reproduction characteristics (boosted
edge values); (b) same screen angles and frequencies with a different
spot function, possibly phase shifted; (c) a dot screen whose frequency
vectors can be generated by the frequency vectors of the interior screen;
(d) a line screen whose frequency vectors can be generated by the
frequency vectors of the interior screen. This generation process is
directed to ensuring that the two screens will be "harmonically matched"
where at least one of the fundamental frequency vectors and harmonics of
the first screen will equal at least one of the fundamental frequency
vectors and harmonics of the second screen.