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Browse Prior Art Database

Printer Font Storage Compression

IP.com Disclosure Number: IPCOM000062766D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Nielson, LR: AUTHOR

Abstract

In wire printers all fonts are stored in ROS as dot images of the required characters. Images are stored in a manner analagous to the way they are printed, in vertical slices, that is, vertical columns of dots with each dot position requiring one bit of storage. It is apparent that, in a printer using fonts that are nine dots high together with the usual 8-bit per byte ROS, straightforward one-for-one storage requires two ROS bytes for each image slice. This is inefficient.

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Printer Font Storage Compression

In wire printers all fonts are stored in ROS as dot images of the required characters. Images are stored in a manner analagous to the way they are printed, in vertical slices, that is, vertical columns of dots with each dot position requiring one bit of storage. It is apparent that, in a printer using fonts that are nine dots high together with the usual 8-bit per byte ROS, straightforward one- for-one storage requires two ROS bytes for each image slice. This is inefficient.

Most characters do not use the 9th dot. This bottom dot appears only in characters with descenders. Therefore the font is divided into two groups, with and without descenders, and each group is assigned a separate section of font ROS. It is apparent that images of characters without descenders require only one ROS byte per slice. Images of characters with descenders are stored with the first eight bytes representing the top eight dots of the first eight slices. The ninth byte represents the ninth dot for the first eight slices, with the high order bit assigned to the first slice, etc. The tenth byte represents the top eight dots of the ninth slice and the high order bit of the eleventh byte represents the ninth bit of the ninth slice. (The low order bits of the eleventh byte are unused.) Thus an image with nine slices of significant data has eleven bytes of image data.

It is apparent that when a character image is to be fetched from font ROS, a test of the cha...