display devices

1. DISPLAY DEVICES
DONE BY
JERIN . M
2nd BCA
13BCA 4219
BABA GHULAM SHAH BADSHAH
UNIVERSITY RAJOURI
Department of computer sciences
Presented to :- Mr Abdul Quyooom
Presented by:-
SUHAIL AHMAD KHANDAY
02-MCA- 2015
COURESE TITLE :- Computer Graphics
PRESENTATION TOPIC :- Display devices

2. A display device is an Output device
for presentation of information for
visual reception . The display systems
are often referred to as Video Monitor
or Video Display Unit (VDU) . Display
devices are designed to project , show ,
exhibit or display softcopy information .

3. Some of the display devices are
• Cathode Ray Tube (CRT)
• Raster Scan Display
• Random Scan Display
• Liquid Crystal Display (LCD)
• Light Emitting Diode (LED)

4. Cathode Ray Tube (CRT)
1. Electron Guns
2. Electron Beams
3. Focusing Coils
4. Deflection Coils
5. Anode Connection
6. Shadow Mask
7. Phosphor layer
8. Close-up of the
phosphor coated inner
side of the screen

5. Diagrammatic representation of CRT

6. A cathode ray tube or CRT is a specialized
vacuum tube in which images are produced
when an electron beam strikes a phosphorescent
surface .
It contains one or more electron guns , and a
fluorescent screen used to view images .
It also contains magnetic deflection coils and
focusing system .

7. Electron Gun

8. Heat is supplied to the cathode by the filament . The
free electrons are then accelerated toward the phosphor
coating by a high positive voltage . A positively
charged metal coating on the inside of the CRT
envelope near the phosphor screen . Intensity of the
electron beam is controlled by setting voltage level on
the control grid . A smaller negative voltage on the
control grid simply decrease the number of electrons
passing through .

9. Accelerating Anode
The accelerating anode is maintained at sufficient
high relative potential to accelerate the beam to
necessary velocity .

10. Focusing System

11. The focusing system is needed to force the electron
beam to converge into a small spot as it strikes
the phosphor .
The electron beam will be focused properly only at the
center of the screen .
As the beam moves to the outer edges of the screen ,
displayed images become blurred .

12. Deflection Systems
The deflection system contains a set of coils mounted at
the neck of the tube . There are two sets of deflecting
plates . One pair of plates is mounted horizontally to
control the vertical deflection , and the other pair is
mounted vertically to control horizontal deflection .

13. Spots of light
Persistence : The time it takes the emitted light from
the screen to decay to one-tenth of its original
intensity .
Resolution : The maximum number of points that can
be displayed without overlap on a CRT .
Aspect Ratio : This numbers gives the ratio of vertical
points to horizontal points necessary to produce equal
length lines in both directions on the screen .

14. Refresh CRT : One way to keep the phosphor
glowing is to redraw the picture repeatedly by
quickly directing the electron beam back over
the same points .
Phosphors : Phosphors has a property to emit
light when electron comes and hits it . This
property is known as phosphorescence .

15. Raster Scan Display
In a raster scan system , the electron beam is
swept across the screen , one row at a time from
top to bottom .
As the electron beam moves across each row , the
beam intensity is turned on and off to create a
pattern of illuminated spots .
Picture definition is stored in a memory area called
the refresh buffer or frame buffer .
Refresh buffer or frame buffer : This memory area
holds the set of intensity values for all the screen
points .

16. Stored intensity values then retrieved from refresh buffer
and “painted ” on the screen one row (scan line) at a
time .

17. On a black – and - white system with one bit per
pixel , the frame buffer is called bitmap .
For system with multiple bits per pixel , the frame
buffer is called pixmap .
Refreshing on raster scan displays is carried out at
the rate 60 to 80 frame per second .

18. Horizontal retrace : The return to the left of the
screen , after refreshing each scan line .

19. Vertical retrace : At the end of each frame ( displayed
in 1/80th to 1/60th of a second ) the electron beam
returns to the top left corner of the screen to begin
the next frame .

20. Random Scan Display
Random scan monitors draw a picture one line at a
time (Vector display , Stroke –writing or calligraphic
displays) .
Refresh rate depends on the number of lines to be
displayed .
Picture definition is now stored as a line-drawing
commands an area of memory referred to as refresh
display file (display list) .

21. The component lines of a picture can be drawn
and refreshed .

22. Random scan displays are designed for line-drawing
applications and can not display realistic shaded scenes.

23. Differences between Random and Raster Scan Display
RASTER SCAN
DISPLAY
RANDOM SCAN
DISPLAY
Picture with better contrast Cannot produce contrast , memory
doesn’t store intensity value of pixel
Less resolution High resolution
Capable of producing curves better Smooth line drawings
Used in systems to display realistic
images
Cannot draw realistic shaded scenes
Cost is less Cost is more
Mainly used for point plotting Line drawing , known as vector
display
Ex . TV sets Ex . Pen Plotter

24. Liquid Crystal Displays (LCD)
Used in small systems , such as calculators , laptop
computers .
Produce a picture by passing polarized light (from
the surrounding or from an internal light source)
through a liquid-crystal material that can be
aligned to either block or transmit the light .

25. Two glass plates , each containing a light polarizer at
right angles to the other plate , sandwich the liquid
crystal materials .
Rows of horizontal transparent conductor & columns
of vertical conductors (put into glass plates) .

26. Polarized light passing through the material is twisted
so that it will pass through the opposite polarizer .
The light is then reflected back to the viewer .
Liquid crystal : These compounds have a crystalline
arrangement of molecules , yet they flow like a
liquid .

27. On State
Off State

28. Light Emitting Diode (LED)
An LED display is a video display which uses light-
emitting diodes . An LED panel is a small display , or
a component of a larger display . They are typically
used outdoors in store signs and billboards . LED
panels are sometimes used as form of lighting , for the
purpose of general illumination , task lighting , or even
stage lighting rather than display .

29. All early devices emitted low-intensity red light , but
modern LEDs are available across the visible ,
ultraviolet and infrared wavelengths , with very high
brightness .
LEDs are based on the semiconductor diode . When the
diode is forward biased (switched on) , electrons are
able to recombine with holes and energy is released in
the form of light . This effect is called
electroluminescence and the color of the light is
determined by the energy gap of the semiconductor .

30. LEDs present many advantages over traditional light
sources including lower energy consumption , longer
lifetime , improved robustness , smaller size and faster
switching . However , they are relatively expensive and
require more precise current and heat management than
traditional light sources .
Applications of LEDs are diverse . They are used as
low-energy indicators but also for replacements for
traditional light sources in general lighting and
automotive lighting . The compact size of LEDs has
allowed new text and video displays and sensors to be
developed , while their high switching rates are useful
in communications technology .

31. LED Display