1 In the name of God Computer Graphics

2 Image Mathematical Model Image Analysis (pattern recognition) Image Synthesis (Rendering) ModelingImage processing

3 Overview Introduction Geometry Interaction Graphic systems 1.Raster Graphics 2.Random Graphics 3.DVST

4 References Computer Graphics, Donald Hearn - M. Pauline Baker 2nd edition - international edition, Prentice Hall, Mathematical Elements For Computer Graphics, D.Roger and J.A. Adams, Mc Graw Hill D Computer Graphics, Alan Watt, Addison Wesley, Computer Graphics, Francis S. Hills, Mac Millan, Publishing Company, 1990.

5 Aims Introduce basic graphics concepts and terminology Base for development computer graphics programmes OpenGL C ProgrammingLiner Algebra

6 Introduction What is Computer Graphic? Applications Hardware

7 Introduction Virtual reality Computer graphics (Photo realistic rendering, Non photo realistic rendering) Image processing image

8 Interactive Computer Graphics User Application Screen input image

9 Supporting knowledge Computer science (algorithms, data structures, …) Mathematics (geometry, numerical, …) Physics (Optics, mechanics, …) Psychology (Colour, perception) Art and design

10 Applications Computer Aided Design (CAD) Computer Aided Geometric Design (CAGD) Entertainment (animation, games, …) Geographic Information Systems (GIS) Visualization (Scientific Vis., Inform. Vis.) Medical Visualization …

11 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

12 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,...

13 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,...

14 Conversion Vector graphics Rasterization, Pattern recognition Scan conversion Raster graphics

15 display devices bitmap screens (CRT & LCD) displays

16 bitmap displays screen is vast number of coloured dots

17 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

18 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

19 Horizontal Deflection Plate Phosphor- Coated Screen Heating Filament Control Grid Accelerating System Vertical Deflection Plate Electron Beam Focusing System Cathode CRT Basics

20 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

21 Output Devices CRT Basics DP DVST (Direct View Storage Tube) Refresh Display Raster - Scan Display Others CPU DP Memory Hard Copy Display Input CRT Displays

22 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)

23 CPU DPU Refresh buffer Input (Display file) CRT Refresh CRT (Vector CRT)

24 CPU DPU CRT Input devices Flood Gun Primary Electron Gun Screen Storage Grid Collector Grid DVST (Direct View Storage Tube)

25 random access flicker-free static (no selective erasing)

26 Fixed frame buffer size Independent of picture complexity input pixel CPU DP CRT Frame Buffer (bit-map) Pixel = Picture element Raster-Scan Display

27 A raster-scan system displays an object as a set of points across each screen scan line (a)(b) (d)(c)

Interlacing

29 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

30 Reflective layer Horizontal polarizer Horizontal grid wires Liquid- crystal layer Vertical grid wires Vertical polarizer Viewing direction LCD ( Liquid Crystal Display ) Basics

31 Other Technology –Plasma-Panel Display –Laser Devices –Three-Dimensional Monitor –Hard Copy Display –Printer –Plotter –3D-printer

32 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

33 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

34 Input Devices/Method Physical Devices Logical Devices Input Mode –Request mode –Event mode –Sample mode

35 Keyboards Physical Devices

36 Dials

37 Touch Panels

38 Light Pen

39 Graphics Tablets

40 3D-Tablet

41 Joystick / Mouse / Trackball

42 Button

43 Voice Systems