Browse Prior Art Database

Halftone Graphics using Program Character Set

IP.com Disclosure Number: IPCOM000089530D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 71K

Publishing Venue

IBM

Related People

DeBry, RK: AUTHOR

Abstract

This system is designed to display halftone images without a large bit buffer or the use of storage tube technology or the like. This is accomplished by defining boundaries of areas of a particular halftone density to delineate a mask and then employing a coded pattern to delineate the boundaries of the particular halftone density to be displayed within that pattern. By testing for redundancies, multiple use of the same storage data can be made, resulting in economies of storage.

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Halftone Graphics using Program Character Set

This system is designed to display halftone images without a large bit buffer or the use of storage tube technology or the like. This is accomplished by defining boundaries of areas of a particular halftone density to delineate a mask and then employing a coded pattern to delineate the boundaries of the particular halftone density to be displayed within that pattern. By testing for redundancies, multiple use of the same storage data can be made, resulting in economies of storage.

Fig. 1 shows a typical system for utilizing this display algorithm. A data processor 10 generates the required masks and patterns and stores the same in 12 and 14. These are compared in 16 and loaded into address positions in a character generator random-access memory 18. Thereafter, processor 10 loads refresh buffer 20 with a sequence of addresses to fetch the information stored in 18 for generating dot pattern "slices" of the "characters" so defined, for display 22 by CRT, gas panel, printer, etc.

This technique will produce halftone images of simple objects on an alphanumeric display device, where the gray scale is produced by varying the distribution of dots in the character boxes which cover the image area. The technique requires no "image" buffer, but does require the ability to define, store, and use "programmable" character sets at the display head.

It is assumed that the image to be reproduced can be described by a set of simple convex planar polygons. Preprocessing of the image is required to do hidden line removal, shading, and to produce a polygon list. Each polygon is represented by an Edge list, beginning with the top-left edge of the polygon and continuing in the order defined by taking edges from left to right in descending y values of the vertices. Take the example shown in Fig. 2. The sorted Edge list for this polygon is shown in Fig. 3.

Basically, the shade specified for the polygon selects a bit pattern which is to be displayed repeatedly within the area covered by the polygon. These bit patterns are predefined and stored as part of a programmable character set definition. For example, if eight gray levels are required, eight bit patterns would be defined.

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