1. Computer Graphics Lecture 4 Computer Graphics Hardware
Graphics Display Devices
(Raster Scan Systems Continued)

2. Components of a Raster Scan System
Raster scan systems consist of a number of processing units:
- CPU
- System Memory
- Frame Buffer
- Video Controller
- Monitor
- System Bus
- I/O Devices

3. Raster Scan Systems

4. Video controller
Raster Scan systems have a special-purpose processor called video/display controller. It is used to control the operations of a display device.
It can directly access the frame buffer.
The function of the video controller is to read the frame buffer and produce the actual image on the screen.

5. Frame Buffer locations and corresponding screen positions are referenced in Cartesian Coordinates.
The origin is defined at the top left screen corner.
Positive x values increase towards the right and positive y values increase towards the top.
Scan lines are labeled from ymax at the top of the screen to 0 at the bottom.
In each line, the screen pixels are labeled from 0 to xmax.
For storing x and y values, two registers are used, x register and y register.

6. When we start scanning from the top left corner of the screen, x register is set to 0 and y register is set to ymax.
As the electron beam moves towards the next pixel, x register is incremented by 1, that is x=x+1.
This process is repeated till x register stores xmax.
After that x register is reset to 0 and y register is decremented by 1, that is y=y-1. This starts the process for next scan line.
All lines are then scanned in the same manner till the electron beam reaches lower right corner, that is y=0 and x=xmax.
Video controller then resets the registers to first pixel position on the top scan line and starts again.

7. Flat Panel devices
CRT monitors are being replaced by flat-panel devices.
Flat panel devices have:
- less weight than CRT’s
- less power requirements than CRT’s
- are thinner than CRT’s
Flat panel devices are used in TV monitors, laptops, calculators, video games, etc.

8. Types of Flat Panel Devices
Plasma Panel displays
Thin-film electroluminescent displays
Light emitting diode (LED)
Liquid Crystal Device (LCD)

9. Plasma Panels

10. Plasma Panels Also called gas discharge displays.
It consist of 2 glass plates.
The area between plates is filled with a mixture of gases including neon.
Vertical conducting ribbons are placed on one plate and horizontal ribbons are placed on the other plate.
Voltages applied to a pair of vertical and horizontal conductors cause the gas to breakdown into glowing plasma of electrons and ions.
Refresh rate of these displays is 60 times/ second

11. Thin-film electroluminescent displays
Similar to plasma panel.
Difference is the area between glass plates is filled with phosphor instead of gas.
Require more power than plasma panel.
Do not display good color.

12. Light Emitting Diode (LED)
LED displays consist of a number of diodes arranged in the form of pixel positions in the display.
When the voltage is applied to the diodes they produce light patterns.
Pixel values are read from the frame buffer.
Diodes

13. Liquid Crystal Device (LCD)
Liquid crystal is a substance in a state between solid and liquid but which has properties of both.
They have crystalline arrangement but they flow like a liquid.
This property is used in LCD’s.

14. LCD

15. It has two glass plates.
One plate has horizontal conductors and other plate has vertical conductors.
The intersection of two conductors forms a pixel position.
In between the plates is a liquid crystal that is twisted.
Light passing through the material is twisted so that it will pass through the other plate.
Light is then reflected back to the users.
To turn off the pixel, voltage is applied to the two conductors that untwists the crystals so that light will not be twisted and will not be passed through the plates.