Computer Graphics 2006/2007 Chapter 1. Introduction 1

Chapter 1Chapter 1

Chapter 1. Introduction1.1 Graphics and computer science1.2 Advantages of interactive graphics1.3 Computer graphics applications1.4 Characteristic devices1.5 Storage formats1.6 The visualization process

Computer Graphics 2006/2007 Chapter 1. Introduction 2

1.1 Graphics and Computer Science

• Prehistory– Whirlwind: Defensive radar system (1951). Computer graphics origin.– DAC-1: IBM & General Motors, 3D representation of a car.

• Advances in the 60’s– Skechpad: Ivan Sutherland, considered as the father of computer gaphics.

created an interactive drawing program.(1961)– SpaceWar: Steve Russell (MIT) designed the first video-game on a DEC

PDP-11. (1961)– First animation shorts to simulate physical effects (gravity, movement, etc.)

(1963)

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– Sutherland (MIT) made up the first head-mounted display with stereoscopy vision (1966)

– First algorithm of hidden surfaces. by Catmull et al. at the Utah University. At the end of 60’s.

– The same team began to have interest in surface shading using color.

• Advances in the 70’s– Introduction of computer graphics in television.– Gouraud presented his famous polygonal surface smoothing

method.(1971)– Microprocessor on the market (1971)– Atari was born in 1972. It is the computer game pioneer.

1.1 Graphics and Computer Science

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– First uses of CG (Computer Graphics) in movies.– Newell at the University of Utah create the famous

teapot, a classical benchmark for visualization algorithms.

– Texturing and Z-Buffer: Catmull’s thesis in 1974.– Phong developed his polygonal surface smoothing

method (1974).– 1975 Baum and Wozniak founded Apple in a garage.– Gates founded Microsoft (1975).– Lucasfilm created the computer graphics division with

the best gurus of the moment (1979).

1.1 Graphics and Computer Science

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• Advances in the 80’s– SIGGRAPH is the most important event in this field.– Whitted published an article about ray tracing technique

(1980)– Carpenter, at Lucasfilm, developed the first rendering engine:

REYES, the Renderman precursor.(1981)– TRON film by Lisberger and Kushner at Disney (beginning of

the 80’s)– Massive sales of graphics terminals: IBM, Tektronix.– The first ISO and ANSI standard for graphics libraries: GKS.– IBM created the Personal Computer PC.

1.1 Graphics and Computer Science

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• Advances in the 90’s and nowadays:– Operative system based on windows for PC (Windows 3.0 at

1990).– 3D-Studio from Autodesk (1990).– Massive use of computers to produce special effects:

Terminator 2 (1991), Disney-Pixar (Toy Story, Bugs, Monsters, inc.), Forrest Gump, Jurassic Park, Lord of the Rings, Starwars episodes I, II and III etc.

– Internet success and 2D and 3D applications for the web.– 3D graphics cards for PC (Voodoo, Nvidia Gforce etc.).

Unstoppable 3D games evolution.– Virtual Reality. A reality.– Nowadays: a must for any application.

1.1 Graphics and Computer Science

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• A better information recognition process• It is possible to offer a higher information density• We can show object relationships (interactivity)• Color can be used• Greater productivity (efficiency, use costs)

1.2 Advantages of interactive graphics

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1.3 Computer graphics applications

• Computer Aided Design– CAD: (Computer Aided Design)

• Graphical tools that allow to design prototypes and evaluate them before producing them

– Most important areas• Industrial design• Architecture• Electric circuits• Integrated and printed circuits

– Most common technique• Design based on constructive primitives,

curved surfaces, etc.– Other possibilities

• Virtual Reality, realistic presentation, constructive suggestions, design analysis, connection with manufacturing system (CAM – Computer Aided Machinery)

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• Presentation graphics– Graphics as a support for reports and

data presentation– Most common areas

• Economy• Statistics • Mathematics• Management

– Most common techniques• Line charts• Pipe charts• 3D surfaces Comidas

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1.3 Computer graphics applications

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• Artistic field– Artistic and commercial objectives

• Logo design• Fine Arts• Animations for advertising

– Techniques and software and software• Programs like “PhotoShop”,

“CorelDraw”, “Freehand” ...• Animation programs• Image processing techniques• “rendering” techniques

1.3 Computer graphics applications

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• Entertainment– Areas

• Movies: (Tron, Toy Story, etc.)• Television (transitions, headers,

etc.)• Computer games

– Techniques• Animation• Realistic visualization• Special effects (Ex. morphing)• Interactivity

1.3 Computer graphics applications

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• Simulation and training– Areas

• Driving simulation– Car driving or flight simulators

• Simulation of processes– Industrial control panels simulation

• Training– Components building and operation, medicine

• Teaching– Children

– Techniques• Real time, Interactivity

– Equipment• Specific equipment (Ex. flight simulators)

– New techniques • virtual reality

1.3 Computer graphics applications

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• Scientific and medical visualization– Graphics visualization of huge amount of

data– Areas

• Medicine (Ex. resonnance)• Engineering (Ex. strengths in a

mechanism) • Physics (Ex. Magnetic fields)• Chemistry (Ex. Molecular interaction)• Mathematics (Ex. equation solution)• Topography and oceanography (Ex.

Terrains and flows)– Techniques

• Codification by color• Level curves• Volume visualization

1.3 Computer graphics applications

Computer Graphics 2006/2007 Chapter 1. Introduction 14Gràfics per Computador

1.4 Characteristic devices: output

Con

nect

ors

BeamGrid

Focusverticaldeflector

horizontaldeflector

Ray

phos

phor

• CRT (Cathode Ray Tube ) characteristics– The beam emits electrons (cathode).– Ray intensity is controlled by the grid.– The focus forces the electrons towards a convergence path.– Deflectors force the ray to point at a specific screen point.– The ray stuns over the phosphor. Phosphor emits lights.– Phosphor emission declines very fast (refreshment required)

Graphic terminal: monitor + controller + memory

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• Vector terminals

• Raster terminals– Screen composed by pixels– The ray traverses the screen from left to right and from top to bottom, lighting

the pixels up– Images is saved in memory (frame-buffer)– The frame-buffer and the screen pixels are traversed simultaneously

converting the color digital codes into ray intensities– Considerations

– Resolution Sizes in pixels– Aliasing– Constant frame-rate– Color possibility (n bits per pixel => 2n colors)– Differences between color modes of high density (16bits/pixel) and true color (24bits/pixel) and

palette modes

1.4 Characteristic devices: output

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Ray

Pixel

Screen

1.4 Characteristic devices: output

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1

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Raster

Frame Buffer

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Raster CRT graphic device with Frame Buffer W/B of one bit plane

Frame Buffer of simple color

1.4 Characteristic devices: output

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Liquid Crystal Displays (LCD)

•Liquid crystals are substances that have properties of liquid and solids

•When light goes through them, the LC forces it to follow the alignment of its molecules

•If an electric source is applied to them, its molecular alignment changes and, therefore, the way the light goes through them

•Displays are formed as LC panels (between two polarized filters) and a back light (normally a cold cathode)

•Most common technologies: DSTN (dual-scan twisted nematic) and TFT (thin film transistor)

•TFT: an extra matrix of transistors (1 per color, RGB, of each pixel) and allows better performance (avoiding ghosting), brightness and contrast

•Advantages over CRT: lower frame-rates (refreshment useful just for animation), less energy consumption, less space

•Disadvantages: fixed resolutions, less vision angles.

•Other technologies: plasma (high voltages to low pressure gases (xenon) that forces the gas to change from gas states to plasma generating light)

1.4 Characteristic devices: output

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•Related with virtual reality and immersive environments: glasses and stereoscopic helmets, caves.

•Printing devices: printers and plotters.

1.4 Characteristic devices: output

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•Keyboard, mouse

•Trackball, digital tablet, optical pen

•3D digitizers, joysticks (2D and 3D)

•3D gloves, motion capture systems

•Specific systems (flight and car driving simulators etc.)

1.4 Characteristic devices: input

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2.5 Storage formats

Representation• Vectors• Bitmap

Definitions• Bitmap representation

• Image is decomposed into pixels. The value of each one is saved individually.• It’s easy to implement and works, with some limitations (e.g. aliasing), with any

type of image• Vector based representation

• Image is represented by a set of geometrical shapes (lines, circles, curves etc.)• The parameters that define the geometric shapes are saved

Applications• Bitmaps: Complex color variations, like real photographs or images that are

difficult to be vectorized.• Vectors: Technical draws, CAD, imagery with simple shapes and coloring.

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2.5 Storage formats

•There are limits or important difficulties in order to represent some images

•Lot of memory required•Huge volume of data•Few flexibility•Fixed resolution

Disadvantages

•More efficient and flexible in many applications•Parts of a scene can be manipulated•Scale changes do not affect to resolution and quality

•Any type of image can be saved•Programming is generally simpler

Advantages

VECTORSBITMAPS

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1.6 The visualization process

Graphics applications=

Hardware (graphics devices + computer) +

Software (model + program + graphic library)

–Model: object data•Geometry, properties (color, material, texture, etc.), hierarchical structures, etc.

–Kernel or application: works with model information•Add, modify and remove data, user’s actions management

–Graphic engine or library: interface betweenapplication and hardware

•Output: data visualization•Input: user’s interaction

Application

Model

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libra

ry

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1.6 The visualization process

•Image synthesis process (visualization process) is the set of 3D and 2D operations undertaken over a computer data model that generate a graphic representation of the model in a physical display

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1.6 The visualization process

Scenetraversal

Modelingtransformation

Viewingtransformation Clipping

ProjectionHidden facesremoval

Lighting

RasterizationScreen

Devicetransformation

3D graphic pipeline

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1.6 El proceso de visualización

2D graphics pipeline

geometric

model

decomposition in

drawing primitivesclipping coordenate system

transformation

rasterization