CSCI 346

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CSCI 346

• Chapter 1
• Graphics Systems and Models

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Agenda

• Homework that is due Wednesday?
• Chapter 1

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Chapter 1

• Computer Graphics
• producing pictures or images using a computer
• 40 years ago
• drawing lines on a cathode ray tube
• Today
• produce images indistinguishable from photos
• produce realistic and animated dinosaurs
• produce 3D worlds

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Computer Graphics Applications

• Display of Information
• Design
• Simulation
• User Interfaces

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Display of Information

• Maps
• GIS
• Spatial Resource Planning (SRP)
• http//earth.google.com/
• Medicine
• MRI and http//mednews.stanford.edu/stanmed/2005fa
  ll/story_images/brain-fmri.jpg
• seeing the unseen
• Visual Human Project
• biology
• electrophysiology
• mathmatics

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Geographic Information System (GIS)

• Stores information about the world as a
  collection of thematic layers that can be linked
  together by geography.
• Uses include
• tracking delivery vehicles,
• planning applications
• modeling global atmospheric circulation.

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GIS
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Spatial Resource Planning

• Spatially-referenced data within engineering,
  operations and distribution network
  management
• Analogous to what Enterprise Resource Planning
  (ERP) solutions do for data held in accounting,
  human resources, procurement and project
  management systems,

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Magnetic Resonance Imaging (MRI) and fMRI

• Uses magnetism and radio waves to produce images

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Ultrasound or CT Scan

• Images are produced by very high frequency sound
  waves or x-rays

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Scientific VisualizationVisual Human Project

• Visible Man Thighs
• from GE Research and Development (Bill Lorenson)

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Scientific VisualizationElectrophysiology

• Computed Potential Distribution on the Cardiac
  Surface during reentry Spiral Tip Meandering,
  an arrhythmia model

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Design

• "the evaluation of alternative solutions and the
  specification of a solution
• CAD / CAM (inc rapid prototyping)
• VLSI design
• generate a possible design, test, use solution as
  a basis for other solution

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Simulation

• Simulators surgeryhttp//www-kismet.iai.fzk.de/V
  RTRAIN/phD_main.html, flight
• Games
• Educational (edutainment) software
• Virtual Reality

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User Interfaces

• Interaction with computers
• Windows
• Icons
• Menus
• Pointing device

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Graphics System

• Processor
• Memory
• Frame buffer
• Output devices
• Input devices

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Processor

• Simple system -- one processor handling
• Normal processing
• Graphics processing
• Rasterization
• Scan conversion

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Pixels and the Frame Buffer

• Picture or image is produced as a array (raster)
  of picture elements (pixels)
• Pixels are stored in part of memory called the
  frame buffer

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Frame Buffer

• depth -- number of bits used for each pixel
• full color systems
• true color systems
• RGB color systems
• 24 or more bits per pixel
• resolution -- number of pixels in the frame
  buffer

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Output Devices

• Dominant type of display is the CRT (cathode ray
  tube)
• CRT emits light for a short time -- a few
  milliseconds.
• For a human to see a steady image the path must
  be retraced or refreshed at least 50x/sechow are
  pixels displayed

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How Are Pixels Displayed?

• Noninterlaced
• displayed row by row
• Interlaced
• Displayed every other row
• 50-75X/second (50-75Hertz)
• 60Hz display refreshes the entire screen 30x/sec
• Commercial TV

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Color CRTs

• 3 phosphors
• arranged in (sometimes triangular) triads
• shadow mask CRT
• screen with small holes ensures only one phosphor
  is excited

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Other Output Devices - Raster

• Liquid Crystal Displays (LCD)
• Plasma Displays
• LED Displays
• Printers

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Input Devices

• Keyboard
• Mouse
• Lightpen
• Joystick
• Data tablet

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Ways to Read an Input Device

• Sampling
• What is its input right now ?
• Event-based
• Wait until the user does something

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3D Input Devices

• 3D Input devices
• Read a 3D position
• Returns 3 numbers to the program an (x,y,z)
  triple
• Examples digitizer, spaceball, glove

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Objects and Viewers3d world

• Object is a constant
• Viewer forms the image
• human viewing system - back of eye
• camera - film plane
• different viewers see the same object differently

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Objects and ViewersPinhole Camera
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Light and Images

• no light -- can't see anything
• simplest scenario one light source
• light from the source strikes various surfaces of
  the objects
• portion is reflected and goes thru the lens to
  the camera
• many variations based on the surface
  characteristics of the object

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Light

• a form of electromagnetic radiation
• the light or visible spectrum is a subset of the
  electromagnetic spectrum (includes radio waves)
• light travels in straight lines from the source
  to the object
• a theoretical point source would have
  monochromatic light emanating equally in all
  directions

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Ray Tracing

• simple concept
• computationally expensive
• scene
• viewer
• objects
• and a light source
• a ray semi infinite line emanates from the
  point source and travels to infinity in some
  direction

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Ray Tracing
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Ray Tracing

• Tracing rays from the light source to the eye.
• Lots of rays are wasted because they never reach
  the eye.

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Ray Tracing

• Trace a new ray toward the light source.

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Ray Tracing
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Ray Tracing - Recursive
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Ray Tracing

• rays travel
• directly to the viewer
• out to infinity
• strike an object and
• mirror - reflect
• diffuse surface - scatter
• transparent - light passes thru the object but is
  changed maybe refracted or bent

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Ray Tracing

• modeled on the real world
• not fast -- in fact so slow that for real time or
  even semi real time graphics we need to look for
  another option

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Homework for this week

• Reading Chapter 2
• Homework 1 - Due 900 AM 01/24/07