CS 445 / 645: Introductory Computer Graphics David Brogan...

CS 445 / 645: CS 445 / 645: Introductory Computer GraphicsIntroductory Computer Graphics

CS 445 / 645: CS 445 / 645: Introductory Computer GraphicsIntroductory Computer Graphics

David BroganDavid Brogan

[email protected]@cs.virginia.eduhttp://www.cs.virginia.edu/~gfx/Courses/2001/Intro.fall.01http://www.cs.virginia.edu/~gfx/Courses/2001/Intro.fall.01

Image from: http://graphics.stanford.edu/~fedkiw/

AdministriviaAdministriviaAdministriviaAdministrivia

SyllabusSyllabus– Instructor/TA coordinatesInstructor/TA coordinates– PrereqsPrereqs– TextsTexts– Assignments Assignments – Grading & Honor CodeGrading & Honor Code– Topic listTopic list

Bio sheetsBio sheets Who’s Adding?Who’s Adding?

Questions?Questions?Questions?Questions?

The BasicsThe BasicsThe BasicsThe Basics

Computer graphics: generating 2D images Computer graphics: generating 2D images of a 3D world represented in a computer.of a 3D world represented in a computer.

Main tasks:Main tasks:– modelingmodeling: creating and representing the geometry : creating and representing the geometry

of objects in the 3D worldof objects in the 3D world– renderingrendering: generating 2D images of the objects: generating 2D images of the objects– animationanimation: describing how objects change in time: describing how objects change in time

Why Study Computer Graphics?Why Study Computer Graphics?Why Study Computer Graphics?Why Study Computer Graphics?

Graphics is coolGraphics is cool– I like to see what I’m doingI like to see what I’m doing– I like to show people what I’m doingI like to show people what I’m doing

Graphics is interestingGraphics is interesting– Involves Involves simulationsimulation, , algorithmsalgorithms, , architecturearchitecture……

I’ll never get an Oscar for my actingI’ll never get an Oscar for my acting– But maybe I’ll get one for my CG special effectsBut maybe I’ll get one for my CG special effects

Graphics is funGraphics is fun

Graphics ApplicationsGraphics ApplicationsGraphics ApplicationsGraphics Applications

Entertainment: CinemaEntertainment: Cinema

Pixar: Monster’s Inc.

Square: Final Fantasy

Graphics Graphics ApplicationsApplicationsGraphics Graphics ApplicationsApplications

Entertainment: GamesEntertainment: Games

GT Racer 3

Polyphony Digital: Gran Turismo 3, A Spec

Graphics Graphics ApplicationsApplicationsGraphics Graphics ApplicationsApplications

Video GamesVideo Games


Medical VisualizationMedical Visualization

MIT: Image-Guided Surgery Project

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Computer Aided Design (CAD)Computer Aided Design (CAD)


Scientific VisualizationScientific Visualization

Display TechnologiesDisplay TechnologiesDisplay TechnologiesDisplay Technologies

Cathode Ray Tubes (CRTs)Cathode Ray Tubes (CRTs)– Most common display device todayMost common display device today– Evacuated glass bottleEvacuated glass bottle– Extremely high voltageExtremely high voltage– Heating element (filament)Heating element (filament)– Electrons pulled towards Electrons pulled towards

anode focusing cylinderanode focusing cylinder– Vertical and horizontal deflection platesVertical and horizontal deflection plates– Beam strikes phosphor coating on front of tubeBeam strikes phosphor coating on front of tube

Electron GunElectron GunElectron GunElectron Gun Contains a filament that, when heated, emits a Contains a filament that, when heated, emits a

stream of electronsstream of electrons Electrons are focused with an electromagnet into a Electrons are focused with an electromagnet into a

sharp beam and directed to a specific point of the sharp beam and directed to a specific point of the face of the picture tubeface of the picture tube

The front surface of the picture tube is coated with The front surface of the picture tube is coated with small phospher dotssmall phospher dots

When the beam hits a phospher dot it glows with a When the beam hits a phospher dot it glows with a brightness proportional to the strength of the beam brightness proportional to the strength of the beam and how often it is excited by the beamand how often it is excited by the beam

Display Technologies: CRTsDisplay Technologies: CRTsDisplay Technologies: CRTsDisplay Technologies: CRTs

Vector DisplaysVector Displays– Anybody remember Anybody remember BattlezoneBattlezone? ? TempestTempest? ?


Vector DisplaysVector Displays– Early computer displays: basically an oscilloscopeEarly computer displays: basically an oscilloscope– Control X,Y with vertical/horizontal plate voltage Control X,Y with vertical/horizontal plate voltage – Often used intensity as ZOften used intensity as Z

Name two disadvantagesName two disadvantages Just does wireframeJust does wireframe

Complex scenes Complex scenes visible flicker visible flicker


Raster DisplaysRaster Displays– Raster: A rectangular array of points or dotsRaster: A rectangular array of points or dots– Pixel: One dot or picture element of the rasterPixel: One dot or picture element of the raster– Scan line: A row of pixelsScan line: A row of pixels


Raster DisplaysRaster Displays– Black and white television: an oscilloscope with a Black and white television: an oscilloscope with a

fixed scan pattern: left to right, top to bottomfixed scan pattern: left to right, top to bottom– To paint the screen, computer needs to To paint the screen, computer needs to

synchronize with the scanning pattern of rastersynchronize with the scanning pattern of raster Solution: special memory to buffer image with scan-out Solution: special memory to buffer image with scan-out

synchronous to the raster. We call this the synchronous to the raster. We call this the framebufferframebuffer..


PhosphersPhosphers– Flourescence: Light emitted while the phospher is Flourescence: Light emitted while the phospher is

being struck by electronsbeing struck by electrons– Phospherescence: Light emitted once the Phospherescence: Light emitted once the

electron beam is removedelectron beam is removed– Persistence: The time from the removal of the Persistence: The time from the removal of the

excitation to the moment when phospherescence excitation to the moment when phospherescence has decayed to 10% of the initial light outputhas decayed to 10% of the initial light output


Raster DisplaysRaster Displays– Frame must be “refreshed” to draw new imagesFrame must be “refreshed” to draw new images– As new pixels are struck by electron beam, others As new pixels are struck by electron beam, others

are decayingare decaying– Electron beam must hit all pixels frequently to Electron beam must hit all pixels frequently to

eliminate flickereliminate flicker– Critical fusion frequencyCritical fusion frequency

Typically 60 times/secTypically 60 times/sec Varies with intensity, individuals, phospher persistence, Varies with intensity, individuals, phospher persistence,

lighting...lighting...


Raster DisplaysRaster Displays– Interlaced ScanningInterlaced Scanning– Assume can only scan 30 times / secondAssume can only scan 30 times / second– To reduce flicker, divide frame into two “fields” of To reduce flicker, divide frame into two “fields” of

odd and even linesodd and even lines

1/30 Sec 1/30 Sec1/60 Sec 1/60 Sec 1/60 Sec 1/60 SecField 1 Field 1Field 2 Field 2

Frame Frame


Raster DisplaysRaster Displays– Scanning (left to right, top to bottom)Scanning (left to right, top to bottom)

Vertical Sync Pulse: Signals the start of the next fieldVertical Sync Pulse: Signals the start of the next field Vertical Retrace: Time needed to get from the bottom of Vertical Retrace: Time needed to get from the bottom of

the current field to the top of the next fieldthe current field to the top of the next field Horizontal Sync Pulse: Signals the start of the new scan Horizontal Sync Pulse: Signals the start of the new scan

lineline Horizontal Retrace: The time needed to get from the end Horizontal Retrace: The time needed to get from the end

of the current scan line to the start of the next scan lineof the current scan line to the start of the next scan line

Display Technology: Color CRTsDisplay Technology: Color CRTsDisplay Technology: Color CRTsDisplay Technology: Color CRTs

Color CRTs are Color CRTs are muchmuch more complicated more complicated– Requires manufacturing very precise geometryRequires manufacturing very precise geometry– Uses a pattern of color phosphors on the screen:Uses a pattern of color phosphors on the screen:

– Why red, green, and blue phosphors?Why red, green, and blue phosphors?

Delta electron gun arrangement In-line electron gun arrangement

Display Technology: Color CRTsDisplay Technology: Color CRTsDisplay Technology: Color CRTsDisplay Technology: Color CRTs

Color CRTs haveColor CRTs have– Three electron gunsThree electron guns– A metal A metal shadow maskshadow mask to differentiate the beamsto differentiate the beams

Display Technology: RasterDisplay Technology: RasterDisplay Technology: RasterDisplay Technology: Raster

Raster CRT pros:Raster CRT pros:– Allows solids, not just wireframesAllows solids, not just wireframes– Leverages low-cost CRT technology (i.e., TVs)Leverages low-cost CRT technology (i.e., TVs)– Bright! Display Bright! Display emitsemits light light

Cons:Cons:– Requires screen-size memory arrayRequires screen-size memory array– Discreet sampling (pixels)Discreet sampling (pixels)– Practical limit on size (call it 40 inches)Practical limit on size (call it 40 inches)– BulkyBulky– Finicky (convergence, warp, etc)Finicky (convergence, warp, etc)

Display Technology: LCDsDisplay Technology: LCDsDisplay Technology: LCDsDisplay Technology: LCDs

Liquid Crystal Displays (LCDs)Liquid Crystal Displays (LCDs)– LCDs: organic molecules, naturally in crystalline LCDs: organic molecules, naturally in crystalline

state, that liquefy when excited by heat or E fieldstate, that liquefy when excited by heat or E field– Crystalline state twists polarized light 90º. Crystalline state twists polarized light 90º.


Liquid Crystal Displays (LCDs)Liquid Crystal Displays (LCDs)– LCDs: organic molecules, naturally in crystalline LCDs: organic molecules, naturally in crystalline

state, that liquefy when excited by heat or E fieldstate, that liquefy when excited by heat or E field– Crystalline state twists polarized light 90ºCrystalline state twists polarized light 90º


Transmissive & reflective LCDs:Transmissive & reflective LCDs:– LCDs act as light valves, not light emitters, and LCDs act as light valves, not light emitters, and

thus rely on an external light source.thus rely on an external light source.– Laptop screen: backlit, Laptop screen: backlit, transmissive displaytransmissive display– Palm Pilot/Game Boy: Palm Pilot/Game Boy: reflective displayreflective display

Display Technology: Plasma Display Technology: Plasma Display Technology: Plasma Display Technology: Plasma

Plasma display panelsPlasma display panels– Similar in principle to Similar in principle to

fluorescent light tubesfluorescent light tubes– Small gas-filled capsules Small gas-filled capsules

are excited by electric field,are excited by electric field,emits UV lightemits UV light

– UV excites phosphorUV excites phosphor– Phosphor relaxes, emits Phosphor relaxes, emits

some other colorsome other color

Display TechnologyDisplay TechnologyDisplay TechnologyDisplay Technology

Plasma Display Panel ProsPlasma Display Panel Pros– Large viewing angleLarge viewing angle– Good for large-format displaysGood for large-format displays– Fairly brightFairly bright

ConsCons– ExpensiveExpensive– Large pixels (~1 mm versus ~0.2 mm)Large pixels (~1 mm versus ~0.2 mm)– Phosphors gradually depletePhosphors gradually deplete– Less bright than CRTs, using more powerLess bright than CRTs, using more power

Display Technology: DMD / DLPDisplay Technology: DMD / DLPDisplay Technology: DMD / DLPDisplay Technology: DMD / DLP Digital Micromirror Devices (projectors) or Digital Micromirror Devices (projectors) or

Digital Light ProcessingDigital Light Processing– Microelectromechanical (MEM) devices, Microelectromechanical (MEM) devices,

fabricated with VLSI techniquesfabricated with VLSI techniques

Display Technology: DMD / DLPDisplay Technology: DMD / DLPDisplay Technology: DMD / DLPDisplay Technology: DMD / DLP

DMDs are truly digital pixelsDMDs are truly digital pixels Vary grey levels by modulating pulse lengthVary grey levels by modulating pulse length Color: multiple chips, or color-wheelColor: multiple chips, or color-wheel Great resolutionGreat resolution Very brightVery bright Flicker problemsFlicker problems

Display Technologies: Display Technologies: Organic LED ArraysOrganic LED ArraysDisplay Technologies: Display Technologies: Organic LED ArraysOrganic LED Arrays Organic Light-Emitting Diode (OLED) ArraysOrganic Light-Emitting Diode (OLED) Arrays

– The display of the future? Many think so.The display of the future? Many think so.– OLEDs function like regular semiconductor LEDsOLEDs function like regular semiconductor LEDs– But they emit lightBut they emit light

Thin-film deposition of organic, light-emitting molecules Thin-film deposition of organic, light-emitting molecules through vapor sublimation in a vacuum.through vapor sublimation in a vacuum.

Dope emissive layers with fluorescent molecules to Dope emissive layers with fluorescent molecules to create color.create color.

http://www.kodak.com/global/en/professional/products/specialProducts/OEL/creating.jhtml

Display Technologies: Display Technologies: Organic LED ArraysOrganic LED ArraysDisplay Technologies: Display Technologies: Organic LED ArraysOrganic LED Arrays OLED pros:OLED pros:

– TransparentTransparent– FlexibleFlexible– Light-emitting, and quite bright (daylight visible)Light-emitting, and quite bright (daylight visible)– Large viewing angleLarge viewing angle– Fast (< 1 microsecond off-on-off)Fast (< 1 microsecond off-on-off)– Can be made large or smallCan be made large or small– Available for cell phones and car stereosAvailable for cell phones and car stereos

OLED cons:OLED cons:– Not very robust, display lifetime a key issueNot very robust, display lifetime a key issue– Currently only passive matrix displaysCurrently only passive matrix displays

Passive matrix: Pixels are illuminated in scanline order, but the lack of Passive matrix: Pixels are illuminated in scanline order, but the lack of phospherescence causes flickerphospherescence causes flicker

Active matrix: A polysilicate layer provides thin film transistors at each pixel, Active matrix: A polysilicate layer provides thin film transistors at each pixel, allowing direct pixel access and constant illum.allowing direct pixel access and constant illum.

CS 445 / 645: Introductory Computer Graphics David Brogan...

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