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Introduction to Computer Graphics Systems.

This book concerns itself with recent hardware developments and the impact these developments have on the discipline of computer-generated graphics. Here then, is a brief introduction to graphics system architectures.

Computer graphics had its start with X-Y plotters. The technology was soon extended to include calligraphic (linedrawing) CRT systems based on refresh-vector hardware and, at a later date, direct-view storage tubes followed by higher performance refresh-vector systems.

Meanwhile, a separate image processing technology had been following its own evolutionary path. Instead of dealing with lines and points randomly positioned anywhere on the display surface, image processing was based on a rectangular array of picture elements or pixels. Digital information defining the state of each pixel was stored in a random-access memory and was used to generate a television-type, raster-scan CRT display in monochrome or full color.

The division between vector graphic (also known as calligraphic) computer graphics and raster-scan image processing has now been bridged by the raster display technology. Low-cost memories have made it economically feasible to assemble high-resolution, fine-detail raster images that all but eliminate the objectionable stair stepping of vector graphic lines when displayed on earlier raster-CRT screens. The ability to fill areas with solid color (and shading) makes raster-CRT screens useful in certain applications. The result is raster scan graphics, which combines the full-color, pixel-by-pixel control potentials of image processing and the line-drawing capabilities of vector graphics in a single display system.

Unfortunately, the move from calligraphic to raster displays has brought new problems. For calligraphic, only the endpoint coordinates of lines needed to be stored, so memory requirements were held to a minimum. Refresh-vector writing speed made it possible to animate the display and to create interactive systems that allowed the operator to control the display in real-time through such input devices as light pens, joysticks, and digitizer tablets. Again, however, only the endpoints needed to be recalculated with each refresh cycle, minimizing the need for high-speed computational capabilities,

However, in raster-scan graphics, each pixel must be computed explicitly. To generate a raster of image, millions of pixels must be computed. The proper value at each pixel is a function of the database (the simulated environment), the viewing position and orientation of the simulated viewer, and the location(s) of the light source(s) in the simulated environment. A long-standing goal of researchers in computer graphics systems has been the development of real-time three-dimensional modeling systems. These systems, which produce a realistic image of a simulated three dimensional environment. have a wide variety of potential uses, from flight simulators for pilot training to interactive computer-aided design (CAD) systems. The most sophisticated of these systems produce, in real-time, images of startling reality.

II. Answer the questions:

1. Say a few words about Computer Graphics early history -

2. What is the raster display technology ?

3. What are the new problems brought by the move from calligraphic to raster displays?