| 摘要 |
<p>A system is described for reformatting halftone data for compression, wherein an original bilevel image is reformatted to produce another bilevel image that allows vertical correlations to be recognized by the compression technique, thus improving compressibility dramatically, with particular suitability for facsimile transmissions. In reformatting it is assumed that a selected halftone frequency H will satisfactorily describe an entire document, and each of successive sets of H consecutive lines are concatenated to form respective single lines. The thus reformatted lines have a clearer halftone periodicity offering greater correlation and permit more efficient coding by well-known standard bilevel compression algorithms (e.g., CCITT G3 (MR) or G4 (MMR)). For an image with unknown pattern frequency, a technique for readily estimating the frequency for use in reformatting the image is described.</p> |
