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Printer Font Compression Technique

IP.com Disclosure Number: IPCOM000087259D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Douglas, GL: AUTHOR

Abstract

When printing wire-matrix characters, only a few "dots" in the character box are used to form the character. This technique reduces by almost one-half the number of bits required to store the font.

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Printer Font Compression Technique

When printing wire-matrix characters, only a few "dots" in the character box are used to form the character. This technique reduces by almost one-half the number of bits required to store the font.

With a printer, such as an IBM matrix printer operating at 30 cycles per second (cps), it is necessary to place dots (five wires) on a horizontal grid of 3 1/3 mils (0.00333 inch) or approximately 30 unique horizontal locations per wire for a wide, proportionally spaced machine (PSM) character. A 10-wire print head can place dots on a grid of 12 mils vertically (wire spacing). However, by indexing forward 6 mils, additional dots can be added to a character when the head traverses the same print line in the opposite direction, providing an effective 6-mil grid vertically.

With an upper-case character 7 dots high (7 wires high) and using the PSM wide character of 30 possible horizontal locations, there are a total of 13 X 30 or 390 possible dot locations which must be specified by the character generator. For each of 96 characters in the character generator, without any compression, it takes approximately 38,000 bits to store a PSM font. The present compression scheme reduces the number of bits required to store the font.

In this compression method, included in the dot data for a column of dots is the column position for that column of dots. For example, if there are only two columns of dots for a character (columns 14 and 18), the "14" and the "18" are made a part of the dot data so that only two columns of information need be stored for that character.

For a 10-wire print head, 10 bits are needed for the dot pattern for a given column. Thus, two bytes as a minimum would be required. Since no more than 30 horizontal locations for columns of dots are needed per character for even the widest character, only fi...