Download Introduction to Computer Graphics

Graphics Device System
1
Graphical System
5 major elements for a computer graphic
system
 Processor
 Memory
 Frame buffer
 Input devices
 Output Devices
2
Output Technology (1/3)

Calligraphic Displays
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
also called vector, stroke or line drawing
graphics
lines drawn directly on phosphor
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display processor directs electron beam according
to list of lines defined in a "display list“
phosphors glow for only a few micro-seconds so
lines must be redrawn or refreshed constantly
deflection speed limits # of lines that can be drawn
without flicker.
3
Output Technology (2/3)

Raster Display
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Display primitives (lines, shaded regions,
characters) stored as pixels in refresh buffer
(or frame buffer)
Electron beam scans a regular pattern of
horizontal raster lines connected by horizontal
retraces and vertical retrace
Video controller coordinates the repeated
scanning
Pixels are individual dots on a raster line
4
Output Technology (cont)
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Bitmap is the collection of pixels
Frame buffer stores the bitmap
Raster display store the display primitives (line,
characters, and solid shaded or patterned area)
Frame buffers


are composed of VRAM (video RAM).
VRAM is dual-ported memory capable of


Random access
Simultaneous high-speed serial output: built-in serial
shift register can output entire scanline at high rate
synchronized to pixel clock.
5
Pros and Cons

Advantages to Raster Displays
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lower cost
filled regions/shaded images
Disadvantages to Raster Displays
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a discrete representation, continuous primitives
must be scan-converted (i.e. fill in the
appropriate scan lines)
Aliasing or "jaggies" Arises due to sampling
error when converting from a continuous to a
discrete representation
6
Basic Definitions



Raster: A rectangular
array of points or dots.
Pixel (Pel): One dot or
picture element of the
raster
Scan line: A row of
pixels
Video raster devices display an
image by sequentially drawing
out the pixels of the scan lines
that form the raster.
7
Resolution

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
Maximum number of points that can be
displayed without overlap on a CRT monitor
Dependent on
 Type of phosphor m
 Intensity to be displayed m
 Focusing and deflection systems m
REL SGI O2 monitors: 1280 x 1024
8
Example

Television

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1/4 MB
~2 MB
Bitmapped display
Color workstation
960x1152x1b
1280x1024x24b
~1 Mb
5 MB
Laserprinters

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
640x480x8b
1920x1080x8b
Workstations

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NTSC
GA-HDTV
300 dpi
2400 dpi
(8.5”x300)(11”x300) 1.05 MB
(8.5”x2400)(11”x2400) ~64 MB
Film (line pairs/mm)

35mm (diagonal) slide (ASA25~125 lp/mm) = 3000
3000 x 2000 x 3 x 12b ~27 MB
9
Aspect Ratio
Frame aspect ratio (FAR) = horizontal/vertical size
TV
HDTV
Page
35mm
Panavision
Vistavision
4:3
16:9
8.5:11 ~ 3/4
3:2
2.35:1 (2:1 anamorphic)
2.35:1 (1.5 anamorphic)
Pixel aspect ratio (PAR) = FAR vres/hres
Nuisance in graphics if not 1
10
Physical Size
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Physical size: Length of the screen
diagonal (typically 12 to 27 inches)
REL SGI O2 monitors: 19 inches
11
Refresh Rates and Bandwidth
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Frames per second (FPS)
Film (double framed) 24 FPS
TV (interlaced) 30 FPS x 1/4 = 8 MB/s
Workstation (non-interlaced) 75 FPS x 5 =
375 MB/s
12
Interlaced Scanning

Scan frame 30 times per second

To reduce flicker, divide frame into two fields—one
consisting of the even scan lines and the other of the odd
scan lines.

Even and odd fields are scanned out alternately to
produce an interlaced image.
1/30 SEC
1/30 SEC
1/60 SEC
1/60 SEC
1/60 SEC
1/60 SEC
FIELD 1
FIELD 2
FIELD 1
FIELD 2
FRAME
FRAME
13
Frame Buffer
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A frame buffer is
characterized by is size, x, y,
and pixel depth.
the resolution of a frame
buffer is the number of pixels
in the display. e.g. 1024x1024
pixels.
Bit Planes or Bit Depth is the
number of bits corresponding
to each pixel. This determines
the color resolution of the
buffer.
Bilevel or monochrome displays have 1
bit/pixel (128Kbytes of RAM)
8bits/pixel -> 256 simultaneous colors
24bits/pixel -> 16 million simultaneous
colors
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Specifying Color
8

direct color :
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each pixel directly
specifies a color value

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e.g., 24bit : 8bits(R)
+ 8bits(G) + 8 bits(B)
8
8
Red
palette-based color :
indirect specification

Green
Blue
use palette (CLUT)

e.g., 8 bits pixel can
represent 256 colors
24 bits plane, 8 bits per color gun.
224 = 16,777,216
15
Lookup Tables

Video controller often uses a lookup table to allow indirection of
display values in frame buffer.

Allows flexible use of colors without lots of frame-buffer memory.
Allows change of display without remapping underlying data
double buffering.
Permits simple animation.
Common sizes: 8 x 12; 8 x 24; 12 x 24.
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16
Color Look-Up Table
CLUT
Frame Buffer
y
127
0
127
2083
00000000
to red
gun
x
00000100
00010011
to green
gun
to blue
gun
255
17
Pseudo Color
RED
GREEN
BLUE
255
254
256 colors chosen from a
palette of 16,777,216.
Each entry in the color map
LUT can be user defined.
3
2
1
0
18
Cathode Ray tube
19
Display Technology

2D Displays
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CRT
LCD (raster)
plasma screen (raster)
Light valves (raster)
Micromirror (raster)
Projected laser (vector)
Direct laser (vector)
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3D Displays
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Stereo presentation
(raster/vector)
Vibrating mirror (vector)
Helical rotor (vector)
LED plate (raster)
Photoactive cube
(raster)
Parabolic mirror (raster)
20
Display Technologies
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Cathode Ray Tubes (CRTs)
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Most common display device today
Evacuated glass bottle (last
of the vacuum tubes)
Heating element (filament)
Electrons pulled towards
anode focusing cylinder
Vertical and horizontal deflection plates
Beam strikes phosphor coating on front of tube
21
Display Technologies: CRTs

Vector Displays
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First computer displays: basically an
oscilloscope
Control X,Y with vertical/horizontal plate
voltage
Often used intensity as Z
22
Vector Display Architecture
23
Display Technologies: CRTs

Raster Displays

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Black and white television: an oscilloscope with a fixed
scan pattern: left to right, top to bottom
Paint entire screen 30 times/sec
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Actually, TVs paint top-to-bottom 60 times/sec, alternating
between even and odd scanlines
This is called interlacing. It’s a hack.
To paint the screen, computer needs to synchronize
with the scanning pattern of raster

Solution: special memory to buffer image with scan-out
synchronous to the raster. We call this the framebuffer.
24
Raster displays Architecture
25
Raster refresh
26
Comparing Raster and Vector (1/2)

advantages of vector:

very fine detail of line drawings (sometimes curves),
whereas raster suffers from jagged edge problem due
to pixels (aliasing, quantization errors)

geometry objects (lines) whereas raster only handles
pixels

eg. 1000 line plot: vector disply computes 2000
endpoints

raster display computes all pixels on each line
27
Comparing Raster and Vector (2/2)

advantages of raster:

cheaper

colours, textures, realism

unlimited complexity of picture: whatever you
put in refresh buffer, whereas vector complexity
limited by refresh rate
28
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
http://www.udayton.edu/~cps/cps460/notes/displays/
29
Display Technology: Color CRTs

Color CRTs have

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Three electron guns
A metal shadow mask to differentiate the
beams
http://www.udayton.edu/~cps/cps460/notes/displays/
30
Display Technology: Raster

CRT (raster) pros:
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Leverages low-cost CRT technology (i.e., TVs)
Bright! Display emits light
Cons:
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Requires screen-size memory array
Discreet sampling (pixels)
Practical limit on size (call it 40 inches)
Bulky
Finicky (convergence, warp, etc)
X-ray radiation…
31
Display Technology: LCDs
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Liquid Crystal Displays (LCDs)
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LCDs: organic molecules, naturally in crystalline state,
that liquefy when excited by heat or E field
Crystalline state twists polarized light 90º.
http://www.udayton.edu/~cps/cps460/notes/displays/
32
LCDs
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Transmissive & reflective LCDs:
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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
http://www.udayton.edu/~cps/cps460/notes/displays/
33
Active-Matrix LCDs
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LCDs must be constantly refreshed, or they fade
back to their crystalline state
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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
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FET transfers charge into capacitor during scan
Capacitor easily holds charge till next refresh
34
Active Matrix LCDs Pros and Cons
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Active-matrix pros: crisper with less ghosting,low
cost, low weight,flat, small size, low power
consumption.
Active-matrix cons: more expensive, small size,
low contrast, slow response
Today, most things seem
to be active-matrix
More on Display
http://www.udayton.edu/~cps/cps460/notes/displays/
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Plasma
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Plasma display panels
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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
36
Plasma Display Panel Pros and Cons
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Plasma Display Panel Pros
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Large viewing angle
Good for large-format displays
Fairly bright
Cons
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Still very expensive
Large pixels (~1 mm versus ~0.2 mm)
Phosphors gradually deplete
Less bright than CRTs, using more power
37
Display Technology: DMDs
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Digital Micromirror Devices (projectors)
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Microelectromechanical (MEM) devices,
fabricated with VLSI techniques
38
DMDs Pros and Cons
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DMDs are truly digital pixels
Vary grey levels by modulating pulse length
Color: multiple chips, or color-wheel
Great resolution
Very bright
Flicker problems
39
FEDs
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Field Emission Devices (FEDs)
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Like a CRT, with many small
electron guns at each pixel
Unreliable electrodes, needs vacuum
Thin, but limited in size
40
Organic LED Arrays
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Organic Light-Emitting Diode (OLED) Arrays
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The display of the future? Many think so.
OLEDs function like regular semiconductor LEDs
But with thin-film polymer construction:
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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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Organic LED Arrays Pros and Cons
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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
OLED cons:
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Not quite there yet (96x64 displays…)
Not very robust, display lifetime a key issue
42
Traditional Input Device (1/4)

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Commonly used today
Mouse-like devices
 mouse
 wheel mouse
 trackball
Keyboards
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Traditional Input Device (2/4)

Pen-based devices
 pressure sensitive
 absolute positioning
 tablet computers
 IPAQ, WinCE machines
 Microsoft eTablet coming
soon
 palm-top devices
 Handspring Visor,
PalmOS™
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Traditional Input Device (3/4)

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Joysticks
 game pads
 flightsticks
 Touchscreens
Microphones
 wireless vs. wired
 headset
45
Traditional Input Device (4/4)
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Digital still and video
cameras, scanners
MIDI devices
 input from electronic
musical instruments
 more convenient
than entering scores
with just a
mouse/keyboard
46
3D Input Device (1/2)

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Electromagnetic trackers
 can be attached to any head, hands, joints,
objects
 Polhemus FASTRAK™(used in Brown’s Cave)
Acoustic-inertial trackers
 Intersense IS-900
http://www.polhemus.com/ftrakds.htm
http://www.isense.com/products/prec/is900/index.htm
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3D Input Device (2/2)

Gloves
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attach electromagnetic tracker to the hand
Pinch gloves
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contact between digits is a “pinch” gesture
in CAVE, extended Fakespace PINCH™
gloves with extra contacts
http://www.fakespacelabs.com/products/pinch.html
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Video Output Devices (1/4)
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Classification
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Stereo
head-mounted displays
 shutter glasses
Degree of immersion
http://robotics.aist-nara.ac.jp/equipments/E conventional desktop
equips/hmd.html
screen
 walkup VR, semiimmersive displays
immersive virtual reality


http://www.virtualresearch.com/index.html
49
Video Output Devices (2/4)
Example of Immersive
Display
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Diffusion Tensor MRI
Brain Visualization at
Brown University
http://www.cs.brown.edu/research/graphics/research/sciviz/brain/brain.html
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Video Output Devices (3/4)
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Desktop
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Vector display
CRT
LCD flatpanel
workstation displays(Sun Lab)
PC and Mac laptops
Tablet computers
Wacom’s display tablet http://www.wacom.com/productinfo/index.cfm
51
Video Output Devices (4/4)

Immersive
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Head-mounted displays (HMD)
Stereo shutter glasses
Virtual Retinal Display (VRD)
CAVE™
http://www.evl.uic.edu/research/template_res_project.php3?indi=27
52
Interactive Input Devices

A graphics work station commonly has one or two
monitors and a range of input devices. These can
include:
Keyboard
May be customized to application.
Can include dials, joysticks.
Other device
Graphics tablet
Light pen
Button devices
3D locators
Voice Input
Mouse
Joystick
Dials and levers
Touch panels
Scanners
53
Hard Copy Devices

Printers
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Non-Impact printers --- Ink jet; laser;
Xerographic;
Electrostatic;
Dye sublimation.
Plotters

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
Flatbed, Beltbed
Multiple pens available
Plotter `languages’
Built in character sets, line styles etc.
54
Hardcopy Technologies

Basically printing on paper, film etc. Some
general issues are:




The resolution of a device is the closest spacing at
which adjacent black and white lines can be
distinguished.
Many devices work by producing (colored) dots, and
image quality vs. dot size or spot size is an issue.
Resolution can be no greater than addressability (lines
per inch) and depends on spot size also on intensity
distribution across spot.
Many devices can create only a few solid colors. Other
colors must be produced by dither patterns.
55
Raster Scan Display Systems

The various hardware architectures for providing
graphics functionality differ on two axes

Processing performed by specialized graphics
hardware.


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Simplest has only video controller.
More complex systems use a graphics display processor with
varying functionality.
Relationship of frame buffer to CPU memory
architecture.
Dual ported
Accessible only to graphics controller
Accessible only over main bus
56
Video Controller
Problems with memory access { 50 ns pixel time (480 x 640 x 60
Hz) is shorter than typical 200 ns RAM cycle time.
- Must fetch multiple pixels per access.
- Can eat up a lot of memory bandwidth.
- Can eat up a lot of main bus bandwidth if so organized.
57
Simple Raster systems (1/2)


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

No special graphics
processing except video
controller. Two basic
frame-buffer mappings.
Single ported frame buffer
Passes video information
over system bus.
Simple and flexible.
Problems with bus
congestion.
58
Simple Raster systems (2/2)


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
Dual ported frame
buffer:
Frame buffer in
special, dual ported
Video RAM.
Unloads bus.
More expensive.
Less exible.
59
Systems with video processors (1/3)


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
Makes sense to put special-purpose hardware
close to video (speed, expense)
May do various scan conversion algorithms, pix
moves, windowing, sometimes rotation of existing
primitives
Commands such as Text, Move, Line, Polygon...
3D stuff as well - hidden surface removal,
shading, texture mapping.
Various architectures.
60
Systems with video processors (2/3)

Graphics processor
has its local memory
and manages the
frame buffer and
specialized graphics
programs.

Typical architecture
for "plug in" graphics
cards.
61
Systems with video processors (3/3)



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Graphics processor is controlled via an instruction
queue.
All data transferred between host memory and
coprocessor memory must go through both CPU
Unimplemented algorithms may be slow, since
host machine has no direct access to the frame
buffer.
May be considerable communication overhead if
coprocessor instruction registers are not memory
mapped.
62
Example: Voodoo
Voodoo chipset manufactured by 3Dfx, Inc.
 3D-only graphics chipset.
 Card manufacturers would build cards
around Voodoo chip
 Came out in 1996 ... probably first
consumer-level 3D accelerator.
 Combined hardware (Voodoo chip) and
software (Direct3D/OpenGL/Glide) solution.

63
Voodoo hardware

Features:
"
"
"
"

Filled 45 Million pixels/s; 1 million triangles/s
Hardware z buffer (16-bit).
Perspective corrected Gouraud-shaded
texture-mapped triangles done in hardware.
Alpha blending (allows transparency)
Software provided polygons, normals and
textures, and did all the geometry
(modelling, viewing) and lighting itself.
64
Example: GeForce 256
Released in 1999.
 One chip solution; 2D and 3D support. 2D
includes MPEG-2 (DVD) decoder.
 RAM from 32MB-128MB
 GeForce GPU (graphics processing unit)
has 23 million transistors ... more than Intel
PIII.

65
Hardware features (1/2)
Still unique for PC board in that it does
transformation and lighting in hardware.
Means more CPU for game physics etc.
 4-stage pipeline:

"
"
"
"

Transformation
Lighting
Triangle setup & clipping
Rasterisation
4 pipelines (16 units).
66
Hardware features (2/2)

Hardware support for:
"
"
"
Phong shaded texture-mapped polygons
Bump mapping
Cube environment mapping
480 Mpixels/s, 15 million polygon/s.
 Extremely fast.
 http://www.nvidia.com. Some very nice
white papers on T & L and cube
enviromapping.

67
GeForce 3
57 million transistor chip (Pentium 4 is ~40
million)
 Released in April 2001.
 Programmability means it's really another
computer within your computer.
 Graphics hardware is moving at 3x Moore's
Law.

68
Render farms





Closely related to Beowulf
clusters
Idea: Use many tightlycoupled off-the-shelf
machines to do rendering
Problem: Dividing the work
But sometimes easy, e.g. one
frame per machine
Example: Titanic water effects
used cluster of about 160
Alphas running Linux/NT.
69