Introduction to Computer Graphics

Report
Introduction to
Computer Graphics
COMP 3003
University College Dublin
1
Recommended Reading
 Computer
–
Foley, Van Dam, Feiner, Huges
 Computer
–
Computer Graphics
Alan Watt
 Computer
–
Graphics
D. Hearn, M. P. Baker
 3D
–
Graphics – Principles and Practice
Graphics
F.S. Hill, JR.
 Fundamentals
–
of Digital Image Processing
Anil K. Jain
University College Dublin
2
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
University College Dublin
3
Contact Details
 Michela
 Room
Bertolotto
B2.21
 Email
: [email protected]
 Web pages (see www.cs.ucd.ie)
– Lecture Notes & Handouts
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4
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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5
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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13
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
–
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
»
–
or Relative
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
–
Continuous: smooth hand motion
»
–
or Continuous
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
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