Visual Display System
Visual Display System :
The primary user interface hardware for displaying these visual media like text, image, graphics,video, and animation is a visual display system. The visual display system contains following three components ,
(i) Monitor, where we view the visual media and the final presentation.
(ii) Video adapter card, an expansion card serving as an interface between the processor and the monitor.
(iii) Video adapter cable, which connects and transmits signals between the adapter card and the monitor.
Monochrome Cathode Ray Tube:
The most common type of monitor used with the multimedia desktop system is based on picture tube called the cathode ray tube (CRT). It is essentially a vacuum sealed glass containing two electrodes, the cathode or negative electrode and the anode or positive electrode. The front face of the tube is coated with a chemical compound called phosphor arranged in the form of rectangular grid of a large number of dots. The material phosphor has a property of emitting glow of light when it is hit by charged particles like electrons. The phosphor dots called pixels, sort for picture elements are responsible for producing an image on the monitor. Other positive electrodes called grids (G1, G2,and G3) are located near the cathode. Near the neck of the CRT are two coils of wire known as the deflection coils. Electron E− beams generated from the cathode are made to hit the phosphor dots generating spots of light and thereby producing the image.
Color Cathode Ray Tube:
The working principle of a color CRT is similar to that of a monochrome CRT, except that here each pixel consists of three colored dots instead of one and is called a triad. These processed phosphor produce lights of color red, green and blue (RGB) and are called primary colors. These are so called because it has been experimentally observed that these three colored lights can combine in various proportions to produce all other colors. Corresponding to the three dots these e− beams from the electrode (also called e−gun), each of which falls on the corresponding dots in various intensity; they produce different proportions of three elementary colored lights which mix together to create the sensation of a specific color in our A perforated screen called a shadow mask prevents the beam from the falling in the gap between the dots. As the e− beam sweeps across the shadow mask, it gets heated up due to e−bombardment on it.