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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