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Data Compression Technique for APA Printer (Change Block Skipping)

IP.com Disclosure Number: IPCOM000052220D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 87K

Publishing Venue

IBM

Related People

Spivey, PR: AUTHOR

Abstract

Presently known techniques for compressing data on, for example, ink je printers takes advantage of the repetitive nature of printed characters. The characters, in general, are of the same line width and are placed on a common base line with similar character heights and raster position.

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Data Compression Technique for APA Printer (Change Block Skipping)

Presently known techniques for compressing data on, for example, ink je printers takes advantage of the repetitive nature of printed characters. The characters, in general, are of the same line width and are placed on a common base line with similar character heights and raster position.

In a machine which must scan and print non-character data, such as an All- Points-Addressable (APA) printer, this algorithm loses much of its efficiency and the volume of data cannot be stored without an excessive amount of memory.

In the proposed algorithm, it is assumed that a replica of the desired medium (photograph, chart, graph, etc.) is scanned by a scanner which outputs in coded form (binary) changes in the scanned medium (light to dark, etc.). The proposed solution takes advantage of data uniformity from scan to scan. It compares the current scan with the previous scan and outputs only the changes. Compression rates of up to 84% have resulted in evaluated samples.

The input to the algorithm assumes the data to be compressed is stored in a buffer of length equal to one scan of a printer, for example, an ink jet printer (40 pel = 40 bits = 5 bytes).

Referring to the drawing (flow chart), the output is stored in two banks: a control bank and a data bank. The control bank indicates which scan, bytes and nibble are changing, and the data bank indicates the new data.

The algorithm rules, as applied to the flow chart, are as follows:

A. Current scan data is compared to previous scan data by scan (40 bits), then by byte (8 bits), and then by nibble (4 bits).

B. For the first scan the previous scan is assumed to be all zeros.

C. If there is no change in the current scan from the previous scan, a single 0 is outputted to the control bank.

D. If there is at least one bit change in the current scan, a single 1 is outputted to the control bank followed by further control describing the changing bytes.

E. After D above, each byte in the current scan is compared with the respective byte in the previous scan.

F. If there is no change in respective bytes, a single 0 is outputted to the control bank for each byte not changing. Four consecutive zeroes af...