b a c kn e x t h o m e csci 346 chapter 1 graphics systems and models
TRANSCRIPT
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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/2005fall/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 Developme
nt (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/VRTRAIN/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 9:00 AM
01/24/07