Abstract :
Error diffusion is a procedure for generating high
quality bilevel images from continuous-tone images so that both
the continuous and halftone images appear similar when observed
from a distance. It is well known that certain objectionable
patterning artifacts can occur in error-diffused images. Here,
we consider a method for adjusting the error-diffusion filter
concurrently with the error-diffusion process so that an error
criterion is minimized. The minimization is performed using
the least mean squares (LMS) algorithm in adaptive signal
processing. Using both raster and serpentine scanning, we show
that such an algorithm produces better halftone image quality
compared to traditional error diffusion with a fixed filter.
Based on the adaptive error-diffusion algorithm, we propose a
method for constructing a halftone image that can be rendered at
multiple resolutions. Specifically, the method generates a halftone
from a continuous tone image such that if the halftone is downsampled,
a binary image would result that is also a high quality
rendition of the continuous-tone image at a reduced resolution.
Such a halftone image is suitable for progressive transmission,
and for cases where rendition at several resolutions is required.
Cases for noninteger scaling factors are also considered.
