I N T R O D U C T I O N T O C O M P U T E R G R A P H I C S Introduction “A Picture is worth a thousand words” “A Computer is worth a millions of pictures”

I N T R O D U C T I O N T O C O M P U T E R G R A P H I C S

Introduction

“A Picture is worth a thousand words”

“A Computer is worth a millions of pictures”

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What is Computer Graphics?

• Graphics is the key technology for communicating ideas, data, and trends in most areas of commerce, Science, Engineering, and Education. Graphics provides one of the natural means for communicating with the computer

• Graphics refers to picture objects, Sketch of building/bridge, Flowcharts, control flow diagrams, bar charts, pie charts etc.,

• Computer Graphics(CG) means creation, storage and manipulation of models and images of picture objects by the aid of computers.

• Such models come from diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures.

• CG includes almost everything on computers that is not text or sound. Today almost every computer can do some graphics, and people have even come to expect to control their computer through icons and pictures rather than just by typing.

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• William Fetter coined term “computer graphics” in 1960 to describe new design methods for creating a series of widely reproduced images on pen plotter exploring cockpit design, using 3D model of human body.

“Perhaps the best way to define computer graphics is to find out what it is not. It is not a machine. It is not a computer, nor a group of computer programs. It is not the know-how of a graphic designer, a programmer, a writer, a motion picture specialist, or a reproduction specialist.

Computer graphics is all these – a consciously managed and documented technology directed toward communicating information accurately and descriptively.”

Computer Graphics, by William A. Fetter, 1966

What is Computer Graphics?

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Classification of CG

• Computer Graphics is broadly classified into three categories.

Based on Type of Object

2-dimensional Graphics(Pixel, Line, circle)

3-dimensional Graphics (Cube, Polyhedron)

Based on User Interaction

Interactive Computer Graphics (ICG)

Non Interactive Computer Graphics

Based on Applications

Business or Presentation Graphics

Scientific Graphics

Scaled drawings

Cartoons,games,and artwork( Entertainment)

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What is Interactive Computer Graphics?

• ICG involve two way communications between the user and computer

• The user controls the contents, structure, and appearance of objects and images by using input devices such as keyboard, mouse, or touch sensitive panel on the screen

• ICG improves the bandwidth of communication between user and m/c. Graphical Interaction has replaced most of the textual interaction.

• ICG is no longer a rarity. It is an integral part of all computer user interfaces, and is indispensable for visualizing 2D,3D, and higher dimensional objects

• First truly interactive graphics system, Sketchpad, pioneered at MIT by Ivan Sutherland for his 1963 Ph.D. thesis

Sketchpad in 1963.

Note: use of a CRT monitor, light pen and function-key panel.

ICG helps in training the Pilots (Flight Simulation).

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Classification of CG (contd..)• Non Interactive CG - User/Observer has

no control over the pictures/images on the screen. – Ex: Titles displayed on TV system or other

computer art.

• Business Graphics - Used to present the quantitative information and performance of an industrial plant or Business organization – Ex: Bar charts, Pie charts etc.,

• Scientific Graphics - Includes program flow charts, control flow diagrams, curve fittings, X-Y plots etc.,

• Scaled drawings - Includes architectural representations, building drawings, bridge sketch, machine drawings etc.,

• Cartography, drafting, raster painting, animation and artwork.

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Hardware Diagram of an ICG

LINE (100,200,300,200)

TEXT (“RAJU”)

LINE (100,200,300,200)

TEXT (“RAJU”)

Refresh Buffer

Display Controller

Display commands

Interface with host computer

Input DevicesInput Devices

Display device

000000000000000000000000000011111111000000000000000000000000000

000000000000000000000000000011111111000000000000000000000000000

Refresh Buffer

Display Controller

Display commands

Interface with host computer

Input DevicesInput Devices

Display device

Architecture of ICG with Raster display

Architecture of ICG with Vector display

CPU Display ProcessorDisplay Device (CRT)

Display Memory

Input Devices

Interactive Devices

Digital Electrical

Visual images

Pictures stored as matrix of intensity values (frame Buffer)

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Representative uses of CG (Applications of CG)

• Used in areas such as - Industry, business, Government, Education, Entertainment, and at home.

• Used in building Graphical User interfaces (GUIs) for most of the application programs.

• Plotting in Business, Science, and technology - Bar charts, histograms, task-scheduling charts, etc., are used to present meaningfully and concisely the trends and patterns gleaned from data, so as to clarify complex phenomena and to facilitate informed decision making.

• Office Automation and Electronic publishing.

• Computer Aided Drafting and Manufacturing (CAD/CAM) - in building the 2D and 3D models, to design components and systems of mechanical, electrical, electronic, and automobile bodies. In design of VLSI chips, and optical systems.

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Representative uses of CG (Applications of CG)

• In Simulation and animation for scientific visualization and entertainment - Computer produced animated movies and displays of the time-varying behavior of real and simulated objects are becoming increasingly popular for scientific and engineering visualization. Using these, we can study the mathematical models of the fluid flow, nuclear and chemical reactions.

• Art and Commerce: In advertising, to express a message, and attract attention. i.e., at museums, supermarkets, Transportation terminals, and hotels.

•  In Process Control systems: Status displays in refineries, power plants, and computer networks, and in Military: to view number and position of vehicles, weapons launched, troop movements, causalities.

•  Cartography: to produce both accurate and schematic representations of geographical and other natural phenomena from measurement data. Ex: Geographic maps, relief maps, exploring maps for drilling and mining, oceanographic charts, weather maps etc.,

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Definitions• Pixel: Smallest unit/part of picture. P(X,Y)• Resolution: Maximum number of pixels that

can be displayed on a screen area without overlapping. Ex: 640x480, 1024x1024, 300x200 ( Depends on the Driver/Adapter)

• Some common Graphics Adapters: CGA, VGA, EGA, Herculous, IBM etc.,

CGA operates in CGAC0, CGAC1, CGAC2 modes

VGA operates in VGALO, VGAHI, VGAMED modes

Note: With respect to different driver/ adapter and the mode , Resolution of the Screen differs.

• Aspect ratio: It is the ratio of Maximum number of pixels on vertical to the Maximum number of pixels on horizontal direction. Usually aspect ratio must be ¾ for better resolution/appearance.

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2D Primitives

Line

X

Y

Polyline

X

Y

Polygon

X

Y

Circle

X

Y

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Curves• Piecewise linear approximation

• Splines: higher-order polynomials– piecewise curvilinear approximation

French Curves Draftman’s Spline

Mathematical Splines

Natural Cubic Spline:

(“duck”)

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Example 3D PrimitivesPolyhedron

Sphere

Polyline

Patch

(spline boundary curve)

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Conceptual Framework for Interactive Graphics

• At the hardware level, a computer receives the input from interactive devices, and outputs an image on the display device.

• At the software level, Application model represents data or objects to be pictured on the screen, which will be retrieved by the Application Program to create and store the pictures . Graphics System retrieves the views from the application program and is responsible for actually generate the picture from the detailed descriptions

• Graphics library/package is intermediary between application and display hardware (Graphics System)

• Application program maps application objects to views (images) of those objects by calling on graphics library

• This hardware and software framework is more than 4 decades old but is still useful, indeed dominant

Applicationmodel

Applicationprogram

GraphicsLibrary

(GL)GraphicsSystem

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Decomposition of a Geometric Model

• Divide and Conquer• Hierarchy of geometrical components• Reduction to primitives (e.g., spheres,

cubes, etc.)• Simple vs. not-so-simple elements (nail

vs. screw)

Head

Shaft

Point

composition

decomposition

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Environmental (R)evolution• Graphics has been key to technology

growth in evolution of computing environments: – graphical user interfaces (GUIs)– visual computing, e.g., desktop publishing,

scientific visualization, information visualization

• Hardware revolution drives everything– every 12-18 months, computer power

improves by factor of 2 in price / performance – Moore’s Law

• Palm TX™, HP I-Paq™ as full PC• iPhone, Blackberry for email/internet• Hallmark singing card, LeapFrog Pad

– graphics memory and network speeds are on even faster exponentials

• Graphics chips in particular have major improvements every six to nine months (e.g. nVidia GeForce™ series, ATI Radeon™ series)

Leapfrog PadTM

Blackberry PearlTM

HP I-PaqTM

nVidia GoForceTM chip (cellphones and PDAs)

Apple iPhoneTM

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Comparison in Hardware

Date

Price

CPU

Memory

Storage

Monitor

Devices

GUI

1984 2007

$2500 $2300

8 MHz 2.8 GHz (Dual)

128KB RAM 2.0GB DDR2 SDRAM

400KB Floppy 500GB Hard Disk

9” Black & White 24” Color512 x 342

68 dpi1920 x 1200

100 dpi

MouseKeyboard

MouseKeyboard

Desktop WIMP Desktop WIMP

+23

x .92

x 350

x 15625

x 1250000

x 2.6x 13.2x 1.5

samesame

same

Original Macintosh

New iMac 24”

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New Forms of Computing:1990-2007

ADVISER: Mars data visualization