Transcript Lecture-1: Overview of Graphics Systems

Prof.Dr. Aydın Öztürk
[email protected]
http://www.ube.ege.edu.tr/~ozturk
Objectives:
The course gives the fundementals of computer graphics.
A subset of topics dealing with two-dimensional drawing
methods and graphics primitives will be discussed
Grading
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Midterm
Assignments
Project
Final
Attendance
25
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50
10
Course Outline
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Mathematics for Computer Graphics
Overview of Graphics Systems
Graphics Output Primitives
Attributes of Graphics Primitives
Geometric Transformations
Two-dimensional Viewing
Midterm
Interactive Input Methods and Graphical User Interfaces
Color Models and Color Applicatios
Computer Animation
Final
Rules
Attendance is required at all times. Students are
expected to come to class fully prepared to discuss
textbook readings and course assignments. Some
percentage of your final grade will be based on your
attendance and class participation.
 Computer Graphics with OpenGL
▪ Third Edition
▪ Hearn and Baker
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Computer Graphics Using OpenGL, 3rd edition/2005,
F.S.Hill, Jr. Prentice Hall
OpenGL Programming Guide, Version 2, 5th edition, D.
Shreiner,M.Woo, J.Neider, T.Davis, Addison-Wesley,
2005, ISBN: 0321335732
Computer graphics: generating 2D images of a 3D
world represented in a computer.
Main tasks:
 modeling: creating and representing the geometry of
objects in the 3D world
 rendering: generating 2D images of the objects
 animation: describing how objects change in time
Graphics is cool
 I like to see what I’m doing
 I like to show people what I’m doing
Graphics is interesting
 Involves simulation, algorithms, architecture…
I’ll never get an Oscar for my acting
 But maybe I’ll get one for my CG special
effects
Graphics is fun
Entertainment: Cinema
Pixar: Monster’s Inc.
Square: Final Fantasy
Entertainment: Cinema
Final Fantasy (Square, USA)
Entertainment: Games
GT Racer 3
Polyphony Digital: Gran Turismo 3, A Spec
Video Games
Medical Visualization
The Visible Human Project
MIT: Image-Guided Surgery Project
Computer Aided Design (CAD)
Scientific Visualization
Everyday Use
 Microsoft’s Whistler OS will use graphics seriously
 Graphics visualizations and debuggers
 Visualize complex software systems
Window system and large-screen interaction metaphors (François Guimbretière)
Outside In (Geometry Center, University of Minnesota)
Reflection models
Copula-Frank
Reference Image
Blue-Metallic Paint
Moore’s Law
Power of a CPU doubles every 18 months / 2 years
Number of transistors on GPU doubles each 6 months.
 Three times Moore’s Law
▪ Good article on Jen-Hsun Huang, Nvidia CEO:
http://www.wired.com/wired/archive/10.07/Nvidia_pr.html
Col. Steve Austin
Worldwide
revenues
$7 Billion Man
$5.6 Billion Man
Retro flashback???
Lee Majors
But…
 Video game sales is roughly same as Hollywood
box office
 Americans bought $3.2 billion in VCRs and DVDs
in 2002
 Total revenues to movie studios is 5 times total
video game revenues
Cathode Ray Tubes (CRTs)
 Most common display device today
 Evacuated glass bottle
 Extremely high voltage
 Heating element
(filament)
 Electrons pulled
towards
anode focusing
cylinder
 Vertical and
horizontal
deflection plates
 Beam strikes
phosphor
coating on front
of tube
Contains a filament that, when heated, emits a stream of
electrons
Electrons are focused with an electromagnet into a sharp beam
and directed to a specific point of the face of the picture tube
The front surface of the picture tube is coated with small
phospher dots
When the beam hits a phospher dot it glows with a brightness
proportional to the strength of the beam and how long it is hit
What’s the largest (diagonal) CRT you’ve seen?
 Why is that the largest?
▪ Evacuated tube == massive glass
▪ Symmetrical electron paths (corners vs. center)
How might one measure CRT capabilities?
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Size of tube
Brightness of phosphers vs. darkness of tube
Speed of electron gun
Width of electron beam
Pixels?
Vector Displays
Vector Displays
 Early computer displays: basically an oscilloscope
 Control X,Y with vertical/horizontal plate voltage
 Often used intensity as Z
Name two disadvantages
 Just does wireframe
 Complex scenes couse visible flicker
Raster Displays
 Raster: A rectangular array of points or dots
 Pixel: One dot or picture element of the raster
 Scan line: A row of pixels
Raster Displays
 Black and white television: an oscilloscope with a fixed scan
pattern: left to right, top to bottom
▪ As beam sweeps across entire face of CRT, beam
intensity changes to reflect brightness
 Analog signal vs. digital display
Can a computer display work like a black and white TV?
 Must synchronize
▪ Your program makes decisions about the intensity signal at
the pace of the CPU…
▪ The screen is “painted” at the pace of the electron gun
scanning the raster
 Solution: special memory to buffer image with scan-out
synchronous to the raster. We call this the framebuffer.
 Digital description to analog signal to digital display
Phosphers
 Flourescence: Light emitted while the
phospher is being struck by electrons
 Phospherescence: Light emitted once the
electron beam is removed
 Persistence: The time from the removal of the
excitation to the moment when
phospherescence has decayed to 10% of the
initial light output
Refresh
 Frame must be “refreshed” to draw new images
 As new pixels are struck by electron beam, others are
decaying
 Electron beam must hit all pixels frequently to eliminate
flicker
 Critical fusion frequency
▪ Typically 60 times/sec
▪ Varies with intensity, individuals, phospher persistence,
lighting...
Raster Displays
 Interlaced Scanning
 Assume can only scan 30 times / second
 To reduce flicker, divide frame into two “fields”
of odd and even lines
1/30 Sec
1/60 Sec
1/60 Sec
Field 1
Field 2
Frame
1/30 Sec
1/60 Sec
1/60 Sec
Field 2
Field 1
Frame
CRT timing
 Scanning (left to right, top to bottom)
▪ Vertical Sync Pulse: Signals the start of the next field
▪ Vertical Retrace: Time needed to get from the bottom of
the current field to the top of the next field
▪ Horizontal Sync Pulse: Signals the start of the new scan
line
▪ Horizontal Retrace: The time needed to get from the end
of the current scan line to the start of the next scan line
Wood chips Chrome spheres
Trash
Daniel Rozin – NYU: (movies) http://fargo.itp.tsoa.nyu.edu/~danny/art.html
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
 Why red, green, and blue phosphors?
Color CRTs have
 Three electron guns
 A metal shadow mask to differentiate the beams
Raster CRT pros:
 Allows solids, not just wireframes
 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)
 CRT technology hasn’t changed much in 50 years
 Early television technology
▪ high resolution
▪ requires synchronization between video signal and
electron beam vertical sync pulse
 Early computer displays
▪ avoided synchronization using ‘vector’ algorithm
▪ flicker and refresh were problematic
 Raster Displays (early 70s)
▪ like television, scan all pixels in regular pattern
▪ use frame buffer (video RAM) to eliminate sync problems
 RAM
▪ ¼ MB (256 KB) cost $2 million in 1971
▪ Do some math…
- 1280 x 1024 screen resolution = 1,310,720 pixels
- Monochrome color (binary) requires 160 KB
- High resolution color requires 5.2 MB
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
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
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
Plasma Display Panel Pros
 Large viewing angle
 Good for large-format displays
 Fairly bright
Cons
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Expensive
Large pixels (~1 mm versus ~0.2 mm)
Phosphors gradually deplete
Less bright than CRTs, using more power
Digital Micromirror Devices (projectors) or Digital Light Processing
 Microelectromechanical (MEM) devices, fabricated with VLSI techniques
DMDs are truly digital pixels
Vary grey levels by modulating pulse length
Color: multiple chips, or color-wheel
Great resolution
Very bright
Flicker problems
Organic Light-Emitting Diode (OLED) Arrays
 The display of the future? Many think so.
 OLEDs function like regular semiconductor LEDs
 But they emit light
▪ Thin-film deposition of organic, light-emitting molecules
through vapor sublimation in a vacuum.
▪ Dope emissive layers
with fluorescent
molecules to create
color.
http://www.kodak.com/global/en/professional/products/specialProducts/OEL/creating.jhtml
OLED pros:
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Transparent
Flexible
Light-emitting, and quite bright (daylight visible)
Large viewing angle
Fast (< 1 microsecond off-on-off)
Can be made large or small
Available for cell phones and car stereos
OLED cons:
 Not very robust, display lifetime a key issue
 Currently only passive matrix displays
▪ Passive matrix: Pixels are illuminated in scanline
order, but the lack of phospherescence causes
flicker
▪ Active matrix: A polysilicate layer provides thin film
transistors at each pixel, allowing direct pixel access
and constant illum.
Display Walls (Princeton)
Stereo
Graphics Hardware
 Frame buffer is anywhere
in system memory
CPU
Frame buffer
Cartesian
Coordinates
System
Memory
System Bus
Video
Controller
Monitor
Graphics Hardware
 Permanent place for
Frame buffer
Cartesian
Coordinates
frame buffer
 Direct connection to
video controller
CPU
System
Memory
Frame
Buffer
System Bus
Video
Controller
Monitor
The need for
synchronization
CPU
synchronized
System
Memory
Frame
Buffer
System Bus
Video
Controller
Monitor
current
previous
The need for
synchronization
 Double buffering
CPU
synchronized
System
Memory
Double
Buffer
System Bus
Video
Controller
Monitor
I/O Devices
System Bus
Display
Processor
CPU
System
Memory
Frame
Buffer
Video
Controller
Monitor
Figure 2.29 from
Hearn and Baker
Store the actual intensities of R, G, and B individually in the
framebuffer
24 bits per pixel = 8 bits red, 8 bits green, 8 bits blue
 16 bits per pixel = ? bits red, ? bits green, ? bits blue
DAC
Store indices (usually 8 bits) in framebuffer
Display controller looks up the R,G,B values before triggering
the electron guns Color Lookup
Pixel color = 14
Table
0
14
Frame Buffer
1024
RGB
DAC
Figure. Renderings of spheres based on the measured “blue-metallic-paint” [2] BRDF
with the eight models. From left to right; Top row: Measured, Ashikhmin-Shirley,
Blinn-Phong, Cook-Torrance, Lafortune, Polynomial model (Ashikhmin-Shirley, p=3).
Bottom row: Oren-Nayar, Ward, Ward-Duer, Polynomial model (Lafortune, p=5),
Polynomial model (Ward, p=5).
Figure. Renderings of a car using copula-based model with different
enviroment maps.