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Digital Raster Image Production Subsystem Employing Unit Space Coded Graphics

IP.com Disclosure Number: IPCOM000082119D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 6 page(s) / 133K

Publishing Venue

IBM

Related People

Galli, EJ: AUTHOR

Abstract

This digital subsystem makes it possible to efficiently transform coded image descriptions (graphics, text, or mixed graphics and text) into raster-scan format for telecommunication to another site, or for controlling raster-driven printers or display devices.

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Digital Raster Image Production Subsystem Employing Unit Space Coded Graphics

This digital subsystem makes it possible to efficiently transform coded image descriptions (graphics, text, or mixed graphics and text) into raster-scan format for telecommunication to another site, or for controlling raster-driven printers or display devices.

The subsystem, shown in Fig. 1, produces a serial digital raster image code from a vector-and-character format code through a sequence of operations, collectively referred to as "unit space coded graphics" (USCG). The main advantage of the USCG method, functionally described in Fig. 2, is that the vector-to-raster data transformation is accomplished without the use of large image buffers or complex high-speed vector generation logic.

Display lists have historically been coded in the "vector" format, wherein directions to construct an image take the form of graphic orders to a display adapter for the production of vectors and characters. The vector format is a convenient way of coding graphics because of the compactness of the code. However, in order to drive raster devices (e.g., raster printers, digital TV displays, facsimile devices), the graphic orders must be converted to the explicit code required by the raster device. This vector-to-raster conversion poses a considerable problem for which practical solutions have not been found, although a number of approaches have been implemented experimentally.

The difficulty arises mainly because the conversion cannot be performed on a line-at-a-time basis, since the vector-coded description imposes no restrictions on the order or direction of vectors comprising an image. Thus, with previous approaches, either the complete raster image was generated and stored before the raster pattern was fed to the device, or the conversion process was repeated for each set of lines which were sequentially assembled and buffered.

The former approach is impractical because of the excessively large storage required. The latter approach attempts to reduce the buffer size required by providing complex dual-buffer controls, as well as high-speed vector generation and bit mapping logic. This has serious limitations for high-resolution printing, and is much too slow for graphic displays.

Raster-scan conversions could be implemented with scan-converter storage tubes. This technique, however, poses serious limitations in regard to resolution and reliability. Another way would be to implement the conversion by computer program, with raster images stored on magnetic tape or disks. However, this approach is severely performance-limited, even with fairly expensive computers. Another limitation is that, for telecommunications applications, expensive communications charnels would be required because of the inefficiency of the raster code.

Although a direct vector-to-raster conversion presents many difficulties, raster devices for text only have been commercially successful, which impl...