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Compression/Decompression Technique for Character Sets

IP.com Disclosure Number: IPCOM000042767D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Foster, RLJ: AUTHOR

Abstract

Character cell oriented dot matrix character sets tend to have certain characteristics which can be used to reduce the data required to define them. The particular characteristics made use of by this algorithm are: A lot of the data in a given cell consists of zeros (non-displayed). Only part of the cell is normally used for the character definition. Horizontal slices within the cell are often repeated. The compression process starts with the selection of a cell and matrix size for the character set and the location of the matrix within the cell. These parameters are then used to perform the full compression. Compression of each cell starts with a scan of all slices within the cell from the first matrix slice to the last cell slice inclusive. The first data bit in the compressed data defines the extent of non- zero data.

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Compression/Decompression Technique for Character Sets

Character cell oriented dot matrix character sets tend to have certain characteristics which can be used to reduce the data required to define them. The particular characteristics made use of by this algorithm are: A lot of the data in a given cell consists of zeros (non-displayed). Only part of the cell is normally used for the character definition. Horizontal slices within the cell are often repeated. The compression process starts with the selection of a cell and matrix size for the character set and the location of the matrix within the cell. These parameters are then used to perform the full compression. Compression of each cell starts with a scan of all slices within the cell from the first matrix slice to the last cell slice inclusive. The first data bit in the compressed data defines the extent of non- zero data. It is set to 0 if the non-zero data is confined within the matrix or to 1 if non-zero data exists between the matrix and the last slice of the cell. The following bits are then set to indicate where non-zero slices exist within the matrix if the first bit is zero, or on top of the matrix to the bottom of the cell if the first bit is 1. A 0 indicates that the slice is all zero, and a 1 indicates that the slice contains non-zero data. The compressed data is then padded with zero bits up to the next byte boundary. If no non-zero data exists in the cell, the cell compression is complete; otherwise, the final stage of the cell compression is to define the non-zero slice data. This is done by starting at the first non-zero slice in the matrix and copying the slice data into the compressed data bit string. The slice data just copied is then compared with the slice data for the next non-zero slice and, if the slices are the same and the slice data does not end on...