Random-Scan System In Computer Graphics

When operated as a random-scan display unit, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn.

Random-Scan monitors draw a picture one line at a time and for this reason, are also referred to as vector displays (or stroke-writing or calligraphic displays).

The component lines of a picture can be drawn and refreshed by a random-scan system in any specified order. A pen plotter operates in a similar way and is an example of a random-scan, hard-copy device.

Architecture of Random-Scan System

In a random scan system as shown in figure 1.14, the picture definition is stored in a part of memory called the refresh display file or refresh buffer.

In this system, images are drawn with the help of line-drawn commands.

The refresh rate on a random-scan system depends on the number of lines to be displayed. Picture definition is now stored as a set of line-drawing commands in an area of memory referred to as the refresh display file. Sometimes the refresh display file is called the display list, display program, or simply the refresh buffer.

Advantages of Random-Scan System

1) It gives a higher resolution.

2) It produces smooth line drawings.

Disadvantages of Random-Scan System

1) It cannot display realistic shades scan.

2) It refreshes less than 60 times per second.