Introduction to Computer Graphics

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Introduction toComputer Graphics

• COMP 3003

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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

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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

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Contact Details

• Michela Bertolotto
• Room B2.21
• Email michela.bertolotto_at_ucd.ie
• Web pages (see www.cs.ucd.ie)
• Lecture Notes Handouts

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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.

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Hardware Issues (Digital Camera Input)

• 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 )

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Digital Camera Input
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Digital Camera Input
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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

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Virtual Reality
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Virtual Reality and Voice Recognition
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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

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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)

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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.)

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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

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Locator Input Devices (cont)

• Discrete or Continuous
• Continuous smooth hand motion
• e.g. mouse, trackball
• Discrete define action
• e.g. cursor-control keys

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Hardware Issues (Display Technology)

• Different output devices 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

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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

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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

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CRT