Summary: Compressible Halftoning
Peter G. Anderson and Changmeng Liu
Rochester Institute of Technology, 102 Lomb Memorial Drive, Rochester, NY 14623-5608, USA
We present a technique for converting continuous gray-scale images to halftone (black and white) images that
lend themselves to lossless data compression with compression factor of three or better.
Our method involves using novel halftone mask structures which consist of non-repeated threshold values.
We have versions of both dispersed-dot and clustered-dot masks, which produce acceptable images for a variety
Using the masks as a sort key allows us to reversibly rearrange the image pixels and partition them into
groups with a highly skewed distribution allowing Huffman compression coding techniques to be applied. This
gives compression ratios in the range 3:1 to 10:1.
Keywords: Image compression, halftone masks, Huffman code, image file formats
Halftone images are black-and-white images formed using patterns whose detailed structures are nearly invisible.
These images thus convey continuous gray-tone pictures to human eyes.
Halftone images' entropies tend to be very high hence unsuitable for typical statistical approaches to data
compression. Many halftone compression approaches involve converting the image back to a gray-level continuous
image, then applying JPEG or a similar method. This works, but the image may be severely degraded ("lossy