Introduction to Computer Graphics

1. Introduction toComputer Graphics COMP 3003

2. Recommended Reading • Computer Graphics – Principles and Practice • Foley, Van Dam, Feiner, Huges • Computer Graphics • D. Hearn, M. P. Baker • 3D Computer Graphics • Alan Watt • Computer Graphics • F.S. Hill, JR. • Fundamentals of Digital Image Processing • Anil K. Jain

3. Course Overview • Hardware, Input & Output - Display Technology • The Eye and image perception • Colours & Colour Models • Object Modelling • 2D Viewing - Windows and Viewports • Transformations - Matrix Representation • Bezier Curves • Clipping • 3D Graphics • Image Compression - JPEG, MPEG, GIF etc. • VRML and the WEB

4. Contact Details • Michela Bertolotto • Room B2.21 • Email : michela.bertolotto@ucd.ie • Web pages (see www.cs.ucd.ie) • Lecture Notes & Handouts

5. Hardware Issues (Input Technology) • Pieces of hardware by which a user enters information into a computer system • mouse, trackball, joystick, voice systems, touch screens etc.

6. Hardware Issues (Digital Camera Input) • Cameras • The image is focused onto a photosensitive surface (such asa charge coupled device (CCD)) line by line to accumulate entire image • The CCD produces current (or simply digital output in newer systems) which is proportional to light intensity (filtered for each of three colour bands) • Different quality/functionality cameras are used:Monochrome, Colour, Smart ( Designed for machine vision applications )

7. Digital Camera Input

8. Digital Camera Input

9. Virtual Reality and Voice Recognition • Virtual reality has generated a completely new set of input devices • Dataglove • Pressure pads • Digitizing arm • Various other tactile and gesture input device • Much research is currently in progress to devise better ways of interacting with the machine • Voice recognition and natural language comprehension are also currently the focus of much research

10. Virtual Reality

11. Virtual Reality and Voice Recognition

12. Hardware Issues (Input Technology) • A major goal in designing graphics packages is device-independence • enhances portability of the application • To provide a level of abstraction for graphics input, most graphics systems support logical input devices • These shield the application from the details of the physical devices available

13. Logical Input Devices • Locator • to indicate a position or orientation • Pick • selects from a displayed entity • Valuator • to input a single real number (Volume Control Dial) • Keyboard • to input a character string • Choice • to select from a set of possible actions or choices (Function Keys)

14. Logical Input Devices • Locator: • Inputs a position (x,y) typically via pointer (mouse/joystick) • Pick: • Identifies a displayed object NOT just an (x,y). • Selects a whole object that is normally associated with a segment via e.g. a lightpen • Choice: • Selects from a set of alternatives: • i.e. integer value from buttons on a box or via a menu selection with lightpen or digitiser, most common is function keys • Valuator: • Inputs a value (real or integer) perhaps from a dial (can be bounded – radio tuner or unbounded – provides relative info.)

15. Locator Input Devices • Absolute or Relative • Absolute: report position with regard to an origin • e.g. data tablet, touch screen • Relative: report position w.r.t. their former position • e.g. mouse, joystick • Direct or Indirect • Direct: user points directly at screen • e.g. light-pen or finger on touch screen • Indirect: user moves cursor on screen with device not on screen • e.g. mouse or joystick

16. Locator Input Devices (cont) • Discrete or Continuous • Continuous: smooth hand motion • e.g. mouse, trackball • Discrete: define action • e.g. cursor-control keys

17. Hardware Issues (Display Technology) • Different outputdevices may be used - monitors, printers, plotters • Most common is the Cathode Ray Tube (CRT) monitor • Horizontal and vertical deflectors focus an electron beam emitted by an electron gun on any spot on a phosphor coated screen • The maximum number of points, or pixels that can be displayed without overlap is called the resolution, e.g. 1024x768, 800x600 etc. • Colour systems have groups of 3 different phosphors, for red, green and blue (the primary colours) • The CRT uses a combination of these phosphors to emit different coloured light

18. Phosphors • Once struck by the electron beam most phosphors relax back to the ground state by emitting a photon of light • This light is called fluorescence, which normally decays in under a millisecond • Some molecules may be further excited, and emit a light call phosphorescence, which decays slower, but still rapidly (15-20 milliseconds) • Therefore, the screen must be refreshed by redrawing the image

19. Phosphors • So phosphors may be characterised by their persistence • (time to decay of emitted light) • High persistence cheap and good for text, bad for animation (original IBM PC monitor) • Low persistence, good for animation, but needs a high refresh rate or flicker can be observed • 50-60 Hz is usually sufficient to avoid flicker

20. CRT