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In the name of God

Computer Graphics

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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

What is Computer Graphic?

Applications

Hardware

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Introduction

Virtual reality

Computer graphics(Photo realistic rendering,

Non photo realistic rendering)

Image processing

image

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Interactive Computer Graphics

User

Application

Screen

input

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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Conversion

Vector graphics

Rasterization, Pattern recognition

Scan conversion

Raster graphics

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display devices

bitmap screens (CRT & LCD)

displays

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bitmap displays

• screen is vast number of coloured dots

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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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12345678

Interlacing

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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

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• Keyboards

Physical Devices

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• Dials

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• Touch Panels

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• Light Pen

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• Graphics Tablets

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• 3D-Tablet

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• Joystick / Mouse / Trackball

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• Button

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• Voice Systems