University College Dublin1 Introduction to Computer Graphics COMP 3003

University College Dublin2 Recommended Reading u Computer Graphics – Principles and Practice – Foley, Van Dam, Feiner, Huges u Computer Graphics – D. Hearn, M. P. Baker u 3D Computer Graphics – Alan Watt u Computer Graphics – F.S. Hill, JR. u Fundamentals of Digital Image Processing – Anil K. Jain

University College Dublin3 Course Overview u Hardware, Input & Output - Display Technology u The Eye and image perception u Colours & Colour Models u Object Modelling u 2D Viewing - Windows and Viewports u Transformations - Matrix Representation u Bezier Curves u Clipping u 3D Graphics u Image Compression - JPEG, MPEG, GIF etc. u VRML and the WEB

University College Dublin4 Contact Details u Michela Bertolotto u Room B2.21 u u Web pages (see –Lecture Notes & Handouts

University College Dublin5 Hardware Issues (Input Technology) u Pieces of hardware by which a user enters information into a computer system – mouse, trackball, joystick, voice systems, touch screens etc.

University College Dublin6 Hardware Issues (Digital Camera Input) u Cameras – The image is focused onto a photosensitive surface (such as a 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 )

University College Dublin7 Digital Camera Input

University College Dublin8 Digital Camera Input

University College Dublin9 Virtual Reality and Voice Recognition u Virtual reality has generated a completely new set of input devices – Dataglove – Pressure pads – Digitizing arm – Various other tactile and gesture input device u Much research is currently in progress to devise better ways of interacting with the machine u Voice recognition and natural language comprehension are also currently the focus of much research

University College Dublin10 Virtual Reality

University College Dublin11 Virtual Reality and Voice Recognition

University College Dublin12 Hardware Issues (Input Technology) u A major goal in designing graphics packages is device-independence – enhances portability of the application u To provide a level of abstraction for graphics input, most graphics systems support logical input devices u These shield the application from the details of the physical devices available

University College Dublin13 Logical Input Devices u Locator – to indicate a position or orientation u Pick – selects from a displayed entity u Valuator – to input a single real number (Volume Control Dial) u Keyboard – to input a character string u Choice – to select from a set of possible actions or choices (Function Keys)

University College Dublin14 Logical Input Devices u Locator: – Inputs a position (x,y) typically via pointer (mouse/joystick) u 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 u 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 u Valuator: – Inputs a value (real or integer) perhaps from a dial (can be bounded – radio tuner or unbounded – provides relative info.)

University College Dublin15 Locator Input Devices u 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 u 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

University College Dublin16 Locator Input Devices (cont) u Discrete or Continuous – Continuous: smooth hand motion » e.g. mouse, trackball – Discrete: define action » e.g. cursor-control keys

University College Dublin17 Hardware Issues (Display Technology) u Different output devices may be used - monitors, printers, plotters u 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

University College Dublin18 Phosphors u Once struck by the electron beam most phosphors relax back to the ground state by emitting a photon of light u This light is called fluorescence, which normally decays in under a millisecond u Some molecules may be further excited, and emit a light call phosphorescence, which decays slower, but still rapidly (15-20 milliseconds) u Therefore, the screen must be refreshed by redrawing the image

University College Dublin19 Phosphors u So phosphors may be characterised by their persistence –(time to decay of emitted light) u High persistence cheap and good for text, bad for animation (original IBM PC monitor) u Low persistence, good for animation, but needs a high refresh rate or flicker can be observed u Hz is usually sufficient to avoid flicker

University College Dublin20 CRT