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Microraster Data Compression by Substitution

IP.com Disclosure Number: IPCOM000079876D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 56K

Publishing Venue

IBM

Related People

Garcia, JE: AUTHOR

Abstract

A coding technique is described which substitutes a single bit for an entire microraster entity, prior to performing data compression by run-length encoding. The substitution performed creates run-length probability distribution which is more efficient to encode than microscanned raw data, using pseudo-hexary type codes.

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Microraster Data Compression by Substitution

A coding technique is described which substitutes a single bit for an entire microraster entity, prior to performing data compression by run-length encoding. The substitution performed creates run-length probability distribution which is more efficient to encode than microscanned raw data, using pseudo-hexary type codes.

A previous method for data compression concatenates microscans to perform run-length encoding. The compression achieved is dependent upon raster height, since probability distribution is not monotonically decreasing; thus making variable-length word codes necessary for efficient encoding.

As background, consider substituting a single "0" bit for some blank entity of a microraster scan. Entities, in decreasing order of relevancy, are suggested to be: sweep, character box, microscan, quarter microscan. The algorithm, for the particular entities suggested, is indicated by the following: 1. If a blank sweep is encountered a 0 is substituted for that sweep (a sweep is a single line of type approximately 1/6'' x

8 1/2''). 2. If a sweep is not blank, a "1" is entered and the sweep is divided into character boxes. 3. If a character box is blank, a 0 is substituted for that box. 4. If a character box is not blank, a 1 is entered and the box is divided into microscans. 5. If a scan is blank, a 0 is substituted for that scan. 6. If a scan is not blank, a 1 is entered and the scan is divided into quarters. 7. If a quarter is blank, a 0 is substituted for that quarter. 8. If a quarter is not blank, a 1 is entered and the bits of data which comprise the quarter are entered. 9. The digitized data thus obtained is run-length encoded.

The technique just mentioned may...