Browse Prior Art Database

Multistage Raster Graphics Symbol Generation System

IP.com Disclosure Number: IPCOM000084462D
Original Publication Date: 1975-Nov-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 6 page(s) / 143K

Publishing Venue

IBM

Related People

Galli, EJ: AUTHOR

Abstract

Described is a new symbol generation system which allows high-resolution raster graphic applications, without using excessively large symbol stores or long raster bit patterns. It also allows cost/performance optimization through a convenient dichotomy of the symbol generation function into hardware-implementable and microprogram-implementable parts.

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Multistage Raster Graphics Symbol Generation System

Described is a new symbol generation system which allows high-resolution raster graphic applications, without using excessively large symbol stores or long raster bit patterns. It also allows cost/performance optimization through a convenient dichotomy of the symbol generation function into hardware- implementable and microprogram-implementable parts.

For high-resolution text printers or display devices operating in the raster mode (e.g., raster graphics printers or TV character displays), the image area is divided into a matrix of unit symbol spaces, and a set of symbol-code-to-raster- patterns that will appear in the unit spaces.

Fig. 1 defines the method and characteristics of current symbol generation techniques. There are up to 2/n/ patterns contained in the store for a symbol code n-bits long, consisting of q lines of p-bits each. The length of each pattern depends on the square of the resolution, since each bit dimension of the unit space (U.S.) (p or q) varies linearly with Q. Therefore, the length of the patterns and the capacity of the symbol store tend to become quite large for larger U.S.'s and high-resolution requirements.

Table 1 illustrates the effect of these dependencies for two U.S. sizes, each evaluated for two different levels of resolution. This is a fundamental problem which requires a completely different approach to symbol generation. Although not critical for low or medium resolution systems (up to 100 elements per inch in X or Y), or for symbol generators containing a modest number of patterns (up to 100-1500, as computer graphics applications are pushed to inevitably higher quality and lower cost objectives, a more practical approach to symbol generation becomes necessary.

The described system overcomes this problem by plitting the symbol generator into at least two parts from an implementation point of view (two or three-stage designs are proposed). With this approach, the capacity of the symbol set. The second stage is best implemented in hardware using a read- only store (ROS) array and the first microcode of a miniprocessor using a limited section of its main store.

Fig. 2 illustrates the general concept and organization of the proposed multistage symbol generation system. Although extensions beyond three stages are possible, as shown for the general case of m stages in Fig. 2, practical considerations will usually limit the design choice to either two or three stages.

The concept is best described by considering a two-stage configuration first. In this design, the two-stage symbol generator is composed of two symbol generators in tandem, S(1) and S(2, each containing a symbol store and appropriate access logic and registers.

The input to the symbol generator is the symbol code C(1) which n(1) bits long. This forms the input to S(1) and defines a set of 2/n/1 entries or patterns (maximum) which stored in S(1).

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Each entry in S(1) is com...