1. Chapter 2 Overview of Graphics Systems
Computer Graphics
Chapter 2
Overview of Graphics Systems

2. 1. Video Display Devices (1/15)
Typical Output Device: Video Monitor
Refresh CRT(Cathode-Ray Tubes)
A beam of electrons (cathode ray)
Electron gun => 전자를 생성
Focusing systems => 전자를 한 곳으로 모음
Deflection systems => 전자의 방향을 제어
Phosphor-coated screen => 빛으로 변환
The light emitted by the phosphor fades very rapidly
→ To redraw the picture repeatedly → Refresh CRT
Computer Vision & Pattern Recognition Lab.

3. 1. Video Display Devices (2/15)
Refresh Cathode-Ray Tubes (cont.)
Electron Gun
Heated metal cathode: To boil off electrons
Control Grid: To control the intensity of the beam
Intensity of the electron beam
Controlled by voltage levels on the control grid
Computer Vision & Pattern Recognition Lab.

4. 1. Video Display Devices (3/15)
Refresh Cathode-Ray Tubes (cont.)
Focusing Systems
To force electron beam to converge to a small cross section as it strikes the phosphor
Electrostatic focusing or Magnetic focusing
Computer Vision & Pattern Recognition Lab.

5. 1. Video Display Devices (4/15)
Refresh Cathode-Ray Tubes (cont.)
Deflection Systems
Can be controlled by either with electric fields or with magnetic fields
Two pairs of deflection plates to control
Vertical deflection
Horizontal deflection
Computer Vision & Pattern Recognition Lab.

6. 1. Video Display Devices (5/15)
Refresh Cathode-Ray Tubes (cont.)
Phosphor-coated screen
The transfer of the CRT beam energy to the phosphor
The electrons in the beam collide with the phosphor coating
Their kinetic energy is absorbed by the phosphor
Converted by friction into heat energy, causes excited phosphor electrons → spot of light
Computer Vision & Pattern Recognition Lab.

7. 1. Video Display Devices (6/15)
Refresh Cathode-Ray Tubes (cont.)
Persistence
How long phosphors continue to emit light after the CRT beam is removed?
Defined as the time it takes the emitted light from the screen to decay to one-tenth of its original intensity
Usually in the range from 10 to 60 microseconds
Lower-persistence phosphor
→ requires higher refresh rates
→ useful for animation
High-persistence phosphor
→ useful for static picture
Computer Vision & Pattern Recognition Lab.

8. 1. Video Display Devices (7/15)
Refresh Cathode-Ray Tubes (cont.)
Resolution
The maximum number of points that can be displayed without overlap on a CRT (Ex: 1280 x 1024)
Spot intensity has a Gaussian distribution
Spot size depends on intensity
Aspect ratio
The ratio of vertical points to horizontal points
Computer Vision & Pattern Recognition Lab.

9. 1. Video Display Devices (8/15)
Raster-Scan Displays
Computer Vision & Pattern Recognition Lab.

10. 1. Video Display Devices (9/15)
Raster-Scan Displays (Cont.)
Raster-Scan display : the most common type of CRT
Refresh Buffer (Frame Buffer)
Picture definition is stored in memory
Pixel or Pel (Picture Element)
Each screen point
Intensity range for each pixel position
Bitmap : black-and white system with one bit per pixel
Pixmap : multiple bit per pixel (Grayscale display)
Computer Vision & Pattern Recognition Lab.

11. 1. Video Display Devices (10/15)
Raster-Scan Displays (cont.)
Refreshing on raster-scan displays
Refresh rates
In units of cycles per second, or Hertz(Hz)
Horizontal retrace
The return to the left of the screen
Vertical retrace
At the end of each frame, the return to the top left corner of the screen to begin the next frame
Interlacing: Each frame is displayed in two passes (fields)
Even-line field and odd-line field
To avoid flicker (Sacrifice in resolution)
Computer Vision & Pattern Recognition Lab.

12. 1. Video Display Devices (11/15)
Random-Scan Displays
Computer Vision & Pattern Recognition Lab.

13. 1. Video Display Devices (12/15)
Random-Scan Displays (cont.) => Skip
CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn
Vector display (stroke-writing or calligraphic display)
Refresh rate depends on the number of lines to be displayed
Picture definition is stored as a set of line-drawing commands
Refresh display file, display list, vector file, display program
Designed to draw all the component lines of a picture 30 to 60 times each second
Designed for line-drawing applications
Can not display realistic shaded scenes
Computer Vision & Pattern Recognition Lab.

14. 1. Video Display Devices (13/15)
Color CRT Monitors
Combination of phosphors (R, G, B)
The two basic techniques
Beam-penetration method
Shadow-mask method
Beam-penetration Method => Skip
Random-scan monitor
Two layers of phosphor (red, green)
A beam of slow electrons → outer red layer
A beam of fast electrons → inner green layer
Screen color controlled by the speed of electrons
Only four colors (red, green, orange, and yellow) are possible
Computer Vision & Pattern Recognition Lab.

15. 1. Video Display Devices (14/15)
Shadow-mask method (Color Television)
Has three phosphor color dots (R, G, B) at each pixel position
The three electron beams are deflected and focused as a group onto the shadow mask.
Various colors can be obtained by varying the intensity levels of three electron beams.
Computer Vision & Pattern Recognition Lab.

16. 1. Video Display Devices (15/15)
Other display devices
Flat-panel display
Plasma Display Panel (PDP) => 전력 소모 많음
Electroluminescent Display (EL)
Liquid Crystal Display (LCD) => 응답속도 느림 (잔상)
Organic Light Emitting Diodes (OLED) => 고가, 개발 중
Stereoscopic display
Computer Vision & Pattern Recognition Lab.

17. 2. Raster-Scan Systems (1/3)
Video Controller
Computer Vision & Pattern Recognition Lab.

18. 2. Raster-Scan Systems (2/3)
Video Controller
Computer Vision & Pattern Recognition Lab.

19. 2. Raster-Scan Systems (3/3)
Raster-Scan Display Processor
Display processor, graphics controller, display coprocessor
Major task : Scan conversion
Graphics commands (lines, circles, …) are scan converted into a set of discrete intensity points in the frame buffer
Computer Vision & Pattern Recognition Lab.

20. Computer Vision & Pattern Recognition Lab.
3. Input devices
Keyboard
Mouse
Trackball
Joystick
Data Glove
Digitizer
Image Scanner
Touch Panel
Light Pen
Voice System
Computer Vision & Pattern Recognition Lab.

21. 4. Graphics Software Standards
GKS (Graphics Kernel System)
PHIGS (Programmer’s Hierarchical Interactive Graphics Standard)
OpenGL
VRML (Virtual-Reality Modeling Language)
Computer Vision & Pattern Recognition Lab.