Abstract
Many binary halftoning algorithms tend to render extreme
tones (i.e., very light or very dark tones) with objectionable dot
distributions. To alleviate this artifact, we introduce a halftone postprocessing
algorithm called the Springs algorithm. The objective of
Springs is to rearrange minority pixels in affected regions for a
smoother, more attractive rendition. In this paper, we describe the
Springs algorithm, and we show results which demonstrate its effectiveness.
The heart of this algorithm is a simple dot-rearrangement
heuristic which results in a more isotropic dot distribution. The approach
is to treat any well-isolated dot as if it were connected to
neighboring dots by springs, and to move it to a location where the
energy in the springs is a minimum. Applied to the whole image, this
could degrade halftone appearance. However, Springs only moves
dots in selected regions of the image. Pixels that are not minority
pixels are not moved at all. Moreover, dot rearrangement is disabled
on and around detected edges, since it could otherwise render
those edges soft and diffuse.
