11.1 Computer Graphics:

Computer graphics

is the discipline of generating images with the aid of

computers

. Today,

computer graphics

is a core technology in digital photography, film, video games, cell phone and

computer

displays, and many specialized applications. ... It is also used for processing image data received from the physical world.

11.2 Application:

Refer 1^st Question & Answer or Click Here

Refer 4^th Question & Answer or Click Here

14.1 CRT == Cathode Ray Tube

Figure 14.1 illustrates the basic operation of a CRT.

A beam of

electrons

(cathode rays), emitted by an

electron gun

, passes through

focusing and deflection systems

that direct the beam toward specified positions on the

phosphor-coated screen

.

The

phosphor

then

emits

a small spot of light at each position contacted by the electron beam. Because the light emitted by the phosphor

fades very rapidly

, some method is needed for maintaining the screen picture.

Fig 14.1

Basic design of a magnetic-deflection CRT

.

One way to do this is to

store

the

picture information

as a

charge distribution

within the CRT. This charge distribution can then be used to keep the

phosphors activated

. However, the most common method now employed for maintaining phosphor glow is to

redraw the picture repeatedly

by quickly directing the electron beam back over the same screen points. This type of display is called a

refresh CRT

, and the frequency at which a picture is redrawn on the screen is referred to as the refresh rate.

Fig 14.2 Operation of an electron gun with an accelerating anode.

Operation of an electron gun with an accelerating anode:

I. The primary components of an electron gun in a CRT are the heated metal cathode and a control grid.

II. The heat is supplied to the cathode by directing a current through a coil of wire, called the filament, inside the cylindrical cathode structure.

III. This causes electrons to be "boiled off" the hot cathode surface.

IV. Inside the CRT envelope, the free, negatively charged electrons are then accelerated toward the phosphor coating by a high positive voltage.

V. Intensity of the electron beam is controlled by the voltage at the control grid.

VI. Since the amount of light emitted by the phosphor coating depends on the number of electrons striking the screen, the brightness of a display point is controlled by varying the voltage on the control grid.

VII. The focusing system in a CRT forces the electron beam to converge to a small cross section as it strikes the phosphor and it is accomplished with either electric or magnetic fields.

VIII. With electrostatic focusing, the electron beam is passed through a positively charged metal cylinder so that electrons along the center line of the cylinder are in equilibrium position.

IX. Deflection of the electron beam can be controlled with either electric or magnetic fields.

X. Cathode-ray tubes are commonly constructed with two pairs of magnetic-deflection coils.

XI. One pair is mounted on the top and bottom of the CRT neck, and the other pair is mounted on opposite sides of the neck.

XII. The magnetic field produced by each pair of coils results in a traverse deflection force that is perpendicular to both the direction of the magnetic field and the direction of travel of the electron beam.