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Computer Graphics
ImageMathematical
Model
Image Analysis(pattern recognition)
Image Synthesis(Rendering)
Modeling Image processing
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Overview
• Introduction
• Geometry
• Interaction
• Graphic systems
1. Raster Graphics
2. Random Graphics
3. DVST
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References• Computer Graphics, Donald Hearn - M. Pauline Baker
2nd edition - international edition, Prentice Hall, 1994
1. Mathematical Elements For Computer Graphics ,
D.Roger and J.A. Adams, Mc Graw Hill 1990.
2. 3D Computer Graphics, Alan Watt, Addison Wesley,
1994.
3. Computer Graphics, Francis S. Hills, Mac Millan,
Publishing Company, 1990.
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Aims
• Introduce basic graphics concepts and terminology
• Base for development computer graphics programmes
OpenGL
C Programming Liner Algebra
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Introduction
Virtual reality
Computer graphics(Photo realistic rendering,
Non photo realistic rendering)
Image processing
image
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Supporting knowledge
• Computer science (algorithms, data structures, …)
• Mathematics (geometry, numerical, …)
• Physics (Optics, mechanics, …)
• Psychology (Colour, perception)
• Art and design
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Applications
• Computer Aided Design (CAD)
• Computer Aided Geometric Design (CAGD)
• Entertainment (animation, games, …)
• Geographic Information Systems (GIS)
• Visualization (Scientific Vis., Inform. Vis.)
• Medical Visualization
• …
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Representations in graphics
Vector Graphics
• Image is represented by continuous geometric objects: lines, curves, etc.
Raster Graphics
• Image is represented as an rectangular grid of coloured squares
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Vector graphics
• Graphics objects: geometry + colour
• Complexity ~ O(number of objects)
• Geometric transformation possible without loss of information (zoom, rotate, …)
• Diagrams, schemes, ...
• Examples: PowerPoint, CorelDraw, ...
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Raster graphics
• Generic
• Image processing techniques
• Geometric Transformation: loss of information
• Complexity ~ O(number of pixels)
• Jagged edges, anti-aliasing
• Realistic images, textures, ...
• Examples: Paint, PhotoShop, ...
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anti-aliasing
Jaggies– diagonal lines that have discontinuities in due to horizontal raster scan
process.
Anti-aliasing– softens edges by using shades of line colour– also used for text
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Cathode ray tube
• Stream of electrons emitted from electron gun, focused and directed by magnetic fields, hit phosphor-coated screen which glows
• used in TVs and computer monitors
electron gun
focussing and deflection
electron beam
phosphor- coated screen
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HorizontalDeflectionPlate
Phosphor-CoatedScreen
HeatingFilament
ControlGrid
AcceleratingSystem
VerticalDeflectionPlate
Electron Beam
FocusingSystem
Cathode
CRT Basics
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• Output Devices
– CRT Displays– Hard Copy Devices
• Input Devices
– Locator– Stroke– String (Keyboard)– Valuator– Choice (Button)– Pick
CPU DP
Input Hard Copy
Display
Graphics Devices
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Output Devices
CRT BasicsDPDVST (Direct View Storage Tube)Refresh DisplayRaster - Scan DisplayOthers
CPU DP
Memory Hard Copy
Display
InputCRT Displays
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Why DP ?
– Scan conversion– Refreshing screen– Interfacing with interactive input devices– Raster operations– Character generation– Additional functions
CPU DP
Memory Input
CRT
DP (Display Processor)
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CPU DPU CRT
Input devices
Flood Gun
PrimaryElectronGun
Screen
Storage Grid
Collector Grid
DVST (Direct View Storage Tube)
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Fixed frame buffer sizeIndependent of picture complexity
input
pixel
CPU DP CRT
Frame Buffer(bit-map)Pixel = Picture element
Raster-Scan Display
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A raster-scan system displays an object as a set of points across each screen scan line
(a) (b)
(d)(c)
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Liquid crystal displays
• Smaller, lighter, and … no radiation problems.
• Found on PDAs, portables and notebooks,… and increasingly on desktop and even for home TV
• also used in dedicted displays:digital watches, mobile phones
• How it works …– Top plate transparent and polarised, bottom plate reflecting.– Light passes through top plate and crystal, and reflects back to eye. – Voltage applied to crystal changes polarisation and hence colour– N.B. light reflected not emitted => less eye strain
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Reflectivelayer
Horizontalpolarizer
Horizontalgrid wires
Liquid-crystallayer
Verticalgrid wires
Verticalpolarizer
Viewingdirection
LCD ( Liquid Crystal Display ) Basics
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• Other Technology– Plasma-Panel Display– Laser Devices– Three-Dimensional Monitor
– Hard Copy Display– Printer– Plotter– 3D-printer
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special displays
Random Scan (Directed-beam refresh, vector display)– draw the lines to be displayed directly
– no jaggies
– lines need to be constantly redrawn
– rarely used except in special instruments
Direct view storage tube (DVST)
– Similar to random scan but persistent => no flicker
– Can be incrementally updated but not selectively erased
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situated displays
• displays in ‘public’ places– large or small– very public or for small group
• display only– for information relevant to location
• or interactive– use stylus, touch sensitive screen
• in all cases … the location matters– meaning of information or interaction is related to the
location
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Input Devices/Method• Physical Devices
• Logical Devices
• Input Mode– Request mode
– Event mode
– Sample mode