Abstract
The emerging international standard for compression of bilevel
images and bi-level documents, JBIG2,provides a mode dedicated for
lossy coding of halftones. The encoding procedure involves
descreening of the bi-levelimage into gray-scale, encoding of the
gray-scale image, and construction of a halftone pattern
dictionary.The decoder first decodes the gray-scale image. Then
for each gray-scale pixel looks up the corresponding
halftonepattern in the dictionary and places it in the
reconstruction bitmap at the position corresponding to the
gray-scale pixel. The coding method is inherently lossy and care
must be taken to avoid introducing artifacts in the reconstructed
image. We describe how to apply this coding method for halftones
created by periodic ordered dithering, by clustered dot screening
(offset printing), and by techniques which in effect dithers with
blue noise, e.g., error diffusion. Besides descreening and
construction of the dictionary, we address graceful degradationand
artifact removal.
Original language | English |
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Journal | Journal of Electronic Imaging |
Volume | 9 |
Issue number | 1 |
Pages (from-to) | 52-60 |
ISSN | 1017-9909 |
Publication status | Published - 2000 |