1. CGMB214: Introduction to Computer Graphics
Topic 2
Overview of Graphics System

2. Objectives
To provide an understanding on the basic feature of graphic hardware components.
To provide an understanding on the operations of a video display device.

3. Cathode Ray Tube Technology
Video Display Devices
Cathode Ray Tube Technology

4. Refresh Cathode Ray Tubes
Video Display Devices
Video Display Devices
CRT Technology
Flat Panel Displays
Refresh Cathode Ray Tubes
Raster Scan Display
Random Scan Display
Colour CRT Monitor
Non Emissive
Display
Emissive Display

5. Refresh Cathode Ray Tubes
Focusing System
Electron Gun
Magnetic Deflection Coils
Phosphor-Coated Screen
Base
Connector Pins

6. Refresh Cathode Ray Tubes: Electron Gun
Heating Filament
Control Grid
Accelerating Anode
Focusing Anode
Cathode

7. Refresh Cathode Ray Tubes: Electron Gun

8. Refresh Cathode Ray Tubes: Electron Gun
Current is directed through filament to supply heat
Electron is being emitted from the hot cathode surface
Control grid is a metal cylinder that is controlled by voltage.
A high negative voltage, will repel electron and stop them from passing
A smaller negative decrease the number of electron passing through
Control Grid
Focusing Anode
Heating Filament
Accelerating Anode
Cathode

9. Refresh Cathode Ray Tubes: Electron Gun
Once an electron is being released and the correct amount of voltage is being supplied by the control grid, the electron will move in a straight line through the control grid
The focusing anode which is charged with hundreds of positive volts, will force the electron beam to converge to it. However, since there are two anode attracting the electron, the electron will continue moving in a straight line
The accelerating anode which is charged with thousand of positive volts will have greater force on attracting the electron beam to converge to it. As focusing anode, the built of the accelerating anode make sure the electron will continue moving in a straight line
Control Grid
Focusing Anode
Heating Filament
Accelerating Anode
Cathode

10. Refresh Cathode Ray Tubes
Magnetic Deflection Coils
Phosphor-Coated Screen
Connector Pins
Base
Electron Gun
Focusing System
The brightness of the of the display point is controlled by the voltage provided by the control grid in the electron gun
The phosphor emits a small spot of light at each position contacted by electron beam
Once the electron beam is emitted by the electron, it will pass through focusing and deflection system that direct the beam toward a specific position on the phosphor-coated screen.

11. Refresh Cathode Ray Tubes
Resolution
A max number of points that can be displayed without overlap on CRT
Typically 1028X1024
High resolution means high definition
Persistence
How long the phosphors will emit light after beam goes
Phosphor with low persistence require higher refresh rate to prevent flicker

12. Refresh Cathode Ray Tubes

13. Raster Scan Displays
The most common type of graphics monitor that employs CRT
The electron beam is swept across the screen one row at a time, from top to bottom
Each row is referred as a scan line
As the electron beam moves across a scan line, the beam intensity is turned on and off to create a pattern of illuminated spots
Screen is divided into smallest element of a rectangular array called pixel or pel (picture element)

14. Raster Scan Displays

15. Raster Scan Displays
Screen Display
Pixels/pels

16. Raster Scan Displays
Raster system commonly characterized by their resolution, which is the number of pixel positions that can be plotted
Another property of video monitors is aspect ratio:
number of pixel columns divided by the number of scan lines that can be displayed by the system
number of horizontal points to vertical points (or vice versa) necessary to produce equal-length lines in both directions on the screen

17. Raster Scan Displays
Picture definition is stored as set of color values for screen points in memory area called refresh buffer or color buffer or frame buffer (frame refers to total screen area).
Frame buffer with one bit per pixel is called bitmap
Frame buffer with multiple bits per pixel is a pixmap.
Refresh rates are described in units of cycles per second (Hertz) where a cycle corresponds to one frame.
Raster scan displays normally perform refreshing at the rate of Hz

18. Raster Scan Displays
Zoom in

19. Random Scan Display
Electron beam is focussed only where lines need to be drawn
Random-scan also known as vector display or stroke-writing display or calligraphic displays
Scene definition stored in a display list as a set of line drawing instruction
Scene is drawn by cycling through the display list drawing one line at a time

20. Random Scan Display
Higher resolution than raster-scan and draw a smoother line because the path beam follows the line path
Designed for specialised line-drawing application e.g. CAD

21. Random Scan Displays

22. Random Scan Display
Zoom in

23. Colour CRT Monitor Two ways of displaying colour: Beam penetration
2 layers of phosphors (red and green)
Colour depends on the speed of the electron beams
Non-expensive way to get colour
Shadow mask
Used in raster scan
Use 3 phosphor colour dots at each pixel (RGB)
CRT needs to have 3 electron guns

24. Colour CRT Monitor: Beam Penetration
fast
moderate
slow
Moderate beam speeds will emits light combination of red and green: orange and yellow
Beam of FAST electron penetrates through the red layer and excites the inner green layer
Beam of SLOW electron excited only the outer layer producing red
Red phosphor layer
Green phosphor layer

25. Colour CRT Monitor: Shadow Mask
Colour variation is produced by varying the intensity level of the electron beams:
Eg. To get yellow, blue gun need to be switch off.
The three electron beams are deflect and focused as a group at a shadow mask. Here it activated a dot triangle
Once all the electrons has been arranged in the shadow mask, it will be released on the correct phosphor triangle on the screen
Each pixel position has three phosphor colour dot: Red, Green and Blue (RGB). Each phosphor emits lights according to their colour.
Shadow mask CRT needs 3 electron guns, one for each colour dot.
The phosphor dots in the triangles are arranged so that each electron beam can only activate its corresponding colour dot when it passes the shadow mask
Electron guns
Shadow mask
Screen

26. Video Display Devices
Flat Panel Displays

27. Flat Panel Displays

28. Flat Panel Displays
Refers to video devices that have reduced volume, weight and power requirement

29. Flat Panel Displays Flat Panel Display
Emissive display
Devices that converts electrical energy to lights
Plasma Panels
Thin-film electroluminescent displays
Light emitting diode (LED)
Non Emissive display
Uses optical effects to convert sunlight/light into graphics patterns
Liquid crystal device

30. Emissive Display:Plasma Panel
Constructed by filling a mixture of gases (usually includes neon), in the region between two glass plates.

31. Emissive Display:Plasma Panel
Glass Plate
Horizontal Conductor/
Address Electrode
Gas (neon, xenon, helium)
Plasma Cell
Vertical Conductor/
Display Electrode
Plasma Cell
RGB phosphor coated
cells
Pixel

32. Emissive Display:Plasma Panel
Horizontal Conductor/
Address Electrode
Gas (neon,
xenon, helium)
Vertical Conductor/
Display Electrode
Plasma Cell
Glass Plate
The photons excite the plasma cell to give off coloured lights
Ionized gas rush to electrodes, collide and emits photons
Voltage difference is created between front and back
The electrodes are being charged
Gas in the middle is being ionized and creating plasma

33. Emissive Display:Thin-Film Electroluminescent
Similar in construction to plasma panels, except that the region between the glass plate is replaced with phosphor
Disadvantages:
Requires more power than plasma
Good colour displays are harder to achieve

34. Emissive Display:Light Emitting Diode (LED)
Matrix of diodes is arranged to form pixel positions in the display
Picture definition is stored in a refresh buffer
Information is read from buffer and converted to voltage levels that are applied to the diode to produce light patterns in display

35. Emissive Display:Light Emitting Diode (LED)

36. Non Emissive Display:Liquid Crystal Display (LCD)
Produce pictures by passing polarised light from the surroundings OR from an internal light source through a liquid-crystal material that can be aligned to either BLOCK or TRANSMIT the light

37. Non Emissive Display:Liquid Crystal Display (LCD)

38. Graphics Workstations and Viewing Systems

39. Graphics Workstations and Viewing Systems
Graphics workstations range from small general-purpose computer systems to multi-monitor facilities, often with ultra-large viewing screen
Personal PC screen
resolution range from 640 x 480 to 1280 x 1024
diagonal screen lengths measure from 12 inches to over 21 inches
High-definition graphics system
resolution up to 2560 x 2048 commonly used in medical imaging, air-traffic control, simulation and CAD
High-end graphics workstations also include large viewing screen often with specialized features such as stereoscopic viewing etc
Multi-panel display screens are used for applications that require “wall-size” viewing area

40. Graphics Workstations and Viewing Systems

41. Input Devices

42. Input Device Keyboards Keypads Touch pads Mice Trackballs Data gloves
Scanner
Reflective (print)
Transparency (film)
Game pads 
Joysticks
Light pens & sensors
Tablets
Force-feedback
Audio/Voice
Microphone
MIDI (Musical Instrument Digital Interface)

43. Input Device Barcode reader Magnetic stripe reader
price scanner or point-of-sale (POS) scanner
Magnetic stripe reader
Credit card reader , ATM – petrol station
MICR – magnetic ink character recognition
Banking environment – check color copies of payroll checks or hand-altered characters

44. Input Device OCR – optical character recognition
Read typewritten text - is used in high-volume financial applications such as payment processing, check reconciliation, and billing. It is also commonly used for high-volume document management in the insurance and healthcare industries

45. Input Device OMR – optical mark recognition
Paper marking - used for time and attendance, labor tracking, inventory management, voting applications, exit surveys, polling, and all manner of questionnaires and evaluation studies

46. Input Device Image scanning devices / digital camera
Ex. Educational environment , New car technology

47. Hard-Copy Devices

48. Hard-Copy Devices Printer Plotter Question : What is the difference?
Taken from :

49. Graphics Software

50. Graphics Software Two broad classification Special purpose packages
Design for non-programmers who want to generate pictures
They don’t have to worry about the graphics procedure
E.g. CAD software, paintbrush
General programming packages
Provides a library of graphics functions that can be used in a programming language such as C/C++, Java or Fortran
E.g. OpenGL, VRML, Java2D, Java3D

51. References http://ppscad.co.uk http://www.ellenfinkelstein.com