David Luebke 04/21/23
CS 551 / 645: Introductory Computer Graphics
David Luebke
http://www.cs.virginia.edu/~cs551
David Luebke 04/21/23
Administrivia
Drop-add forms
David Luebke 04/21/23
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
David Luebke 04/21/23
Display Technology: Color CRTs
Color CRTs have– Three electron guns– A metal shadow mask to differentiate the beams
David Luebke 04/21/23
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
David Luebke 04/21/23
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
David Luebke 04/21/23
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
David Luebke 04/21/23
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
David Luebke 04/21/23
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
David Luebke 04/21/23
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?
David Luebke 04/21/23
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
David Luebke 04/21/23
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
David Luebke 04/21/23
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)
David Luebke 04/21/23
The End
Next up: UNIX, etc.
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