David Luebke 04/21/23

CS 551 / 645: Introductory Computer Graphics

David Luebke

cs551@cs.virginia.edu

http://www.cs.virginia.edu/~cs551

David Luebke 04/21/23

Administrivia

Drop-add forms

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Display Technologies: Recap

Cathode Ray Tube (CRT)– Vector displays:

Oscilloscope; computer draws lines on screen Pros: bright, crisp lines Cons: Just lines, and a limit on display complexity

– Raster displays Fixed scan pattern: left-to-right, top-to-bottom Special memory on computer synchronized to scan out with

raster pattern of electron gun Pros: Solid objects, image complexity only limited by memory

size and scan-out rates Cons: Discrete sampling artifacts (aliasing), fast memory very

expensive (less true now than then)

David Luebke 04/21/23

Display Technology: Color CRTs

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

Delta electron gun arrangement In-line electron gun arrangement

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Display Technology: Color CRTs

Color CRTs have– Three electron guns– A metal shadow mask to differentiate the beams

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Display Technology: Raster

CRT (raster) pros:– Leverages low-cost CRT technology (i.e., TVs)– Bright! Display emits light

Cons:– Requires screen-size memory array– Discreet sampling (pixels)– Practical limit on size (call it 40 inches)– Bulky– Finicky (convergence, warp, etc)– X-ray radiation…

David Luebke 04/21/23

Display Technology: LCDs

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

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

David Luebke 04/21/23

Display Technology: LCDs

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

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

David Luebke 04/21/23

Display Technology: LCDs

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

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

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Display Technology: Active-Matrix LCDs LCDs must be constantly refreshed, or they

fade back to their crystalline state– Refresh applied in a raster-like scanning pattern– Passive LCDs: short-burst refresh, followed by

long slow fade in which LCD is between On & Off– Not very crisp, prone to ghosting

Active matrix LCDs have a transistor and capacitor at every cell– FET transfers charge into capacitor during scan– Capacitor easily holds charge till next refresh

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Display Technology: Active Matrix LCDs Active-matrix pros: crisper with less ghosting Active-matrix cons: more expensive Today, most things seem

to be active-matrix

More on LCDs: http://144.126.176.216/Displays/c3_s1.htm

David Luebke 04/21/23

Display Technology: Plasma

Plasma display panels– Similar in principle to

fluorescent light tubes– Small gas-filled capsules

are excited by electric field,emits UV light

– UV excites phosphor– Phosphor relaxes, emits

some other color

David Luebke 04/21/23

Display Technology

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

Cons– Still very expensive– Large pixels (~1 mm versus ~0.2 mm)– Phosphors gradually deplete– Less bright than CRTs, using more power

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Display Technology: DMDs

Digital Micromirror Devices (projectors)– Microelectromechanical (MEM) devices,

fabricated with VLSI techniques

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Display Technology: DMDs

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

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Display Technologies: FEDs

Field Emission Devices (FEDs)– Like a CRT, with many small

electron guns at each pixel– Unreliable electrodes, needs vacuum– Thin, but limited in size

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

– The display of the future? Many think so.– OLEDs function like regular semiconductor LEDs– But with thin-film polymer construction:

Thin-film deposition or vacuum deposition process…not grown like a crystal, no high-temperature doping

Thus, easier to create large-area OLEDs

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Display Technologies: Organic LED Arrays OLED pros:

– Transparent– Flexible– Light-emitting, and quite bright (daylight visible)– Large viewing angle– Fast (< 1 microsecond off-on-off)– Can be made large or small

OLED cons:– Not quite there yet (96x64 displays…)– Not very robust, display lifetime a key issue

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Framebuffers

So far we’ve talked about the physical display device

How does the interface between the device and the computer’s notion of an image look?

Framebuffer: A memory array in which the computer stores an image– On most computers, separate memory bank from

main memory (why?)– Many different variations, motivated by cost of

memory

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Framebuffers: True-Color

A true-color (aka 24-bit or 32-bit) framebuffer stores one byte each for red, green, and blue

Each pixel can thus be one of 224 colors Pay attention to

Endian-ness How can 24-bit

and 32-bit mean the same thing here?

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Framebuffers: Indexed-Color

An indexed-color (8-bit or PseudoColor) framebuffer stores one byte per pixel

This byte indexes into a color map: How many colors

can a pixel be? Cute trick:

color-map animation

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Framebuffers: Hi-Color

Hi-Color is a popular PC SVGA standard Packs R,G,B into 16-bits with 5 bits/channel:

Each pixel can be one of 215 colors Hi-color images can exhibit worse

quantization artifacts than a well-mapped 8-bit image

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UNIX

Over half the class dreams in C and rules the UNIX world with an iron fist

Thus, we will move the UNIX class to an optional evening section (or two, if necessary) led by Dale– Getting around

– Using make and makefiles

– Using gdb We will use 2 libraries: OpenGL and Xforms

– OpenGL native on SGIs; on other platforms Mesa

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XForms Intro

Xforms: a toolkit for easily building Graphical User Interfaces, or GUIs– See http://bragg.phys.uwm.edu/xforms– Lots of widgets: buttons, sliders, menus, etc.– Plus, an OpenGL canvas widget that gives us a

viewport or context to draw into with GL or Mesa.

Quick tour now You’ll learn the details yourself in

Assignment 1 (Monday)

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The End

Next up: UNIX, etc.