1. Graphics Device System

2. Graphical System 5 major elements for a computer graphic system
Processor
Memory
Frame buffer
Input devices
Output Devices

3. Output Technology (1/3) Calligraphic Displays
also called vector, stroke or line drawing graphics
lines drawn directly on phosphor
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.

4. Output Technology (2/3) Raster Display
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

5. Output Technology (cont)
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.

6. Pros and Cons Advantages to Raster Displays
lower cost
filled regions/shaded images
Disadvantages to Raster Displays
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

7. 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.

8. Resolution
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

9. Example Television Workstations Laserprinters Film (line pairs/mm)
NTSC x480x8b 1/4 MB
GA-HDTV x1080x8b ~2 MB
Workstations
Bitmapped display 960x1152x1b ~1 Mb
Color workstation 1280x1024x24b 5 MB
Laserprinters
300 dpi (8.5”x300)(11”x300) MB
2400 dpi (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

10. Aspect Ratio Pixel aspect ratio (PAR) = FAR vres/hres
Frame aspect ratio (FAR) = horizontal/vertical size
TV :3
HDTV :9
Page :11 ~ 3/4
35mm :2
Panavision :1 (2:1 anamorphic)
Vistavision :1 (1.5 anamorphic)
Pixel aspect ratio (PAR) = FAR vres/hres
Nuisance in graphics if not 1

11. Physical Size
Physical size: Length of the screen diagonal (typically 12 to 27 inches)
REL SGI O2 monitors: 19 inches

12. Refresh Rates and Bandwidth
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

13. 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
1/60 SEC
FIELD 1
FIELD 2
FRAME

14. Frame Buffer
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

15. Specifying Color direct color :
Green
Red
Blue 8
direct color :
each pixel directly specifies a color value
e.g., 24bit : 8bits(R) + 8bits(G) + 8 bits(B)
palette-based color : indirect specification
use palette (CLUT)
e.g., 8 bits pixel can represent 256 colors
24 bits plane, 8 bits per color gun.
224 = 16,777,216

16. 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.

17. Color Look-Up Table Frame Buffer CLUT 127 255 2083 00000000 00000100
255
2083
to blue
gun
to green
to red x y

18. Pseudo Color

19. Cathode Ray tube

20. Display Technology 2D Displays 3D Displays CRT LCD (raster)
plasma screen (raster)
Light valves (raster)
Micromirror (raster)
Projected laser (vector)
Direct laser (vector)
3D Displays
Stereo presentation (raster/vector)
Vibrating mirror (vector)
Helical rotor (vector)
LED plate (raster)
Photoactive cube (raster)
Parabolic mirror (raster)

21. Display Technologies Cathode Ray Tubes (CRTs)
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

22. Display Technologies: CRTs
Vector Displays
First computer displays: basically an oscilloscope
Control X,Y with vertical/horizontal plate voltage
Often used intensity as Z

23. Vector Display Architecture

24. Display Technologies: CRTs
Raster Displays
Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom
Paint entire screen 30 times/sec
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.

25. Raster displays Architecture

26. Raster refresh

27. 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 line plot: vector disply computes endpoints
raster display computes all pixels on each line

28. 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

29. 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

30. Display Technology: Color CRTs
Color CRTs have
Three electron guns
A metal shadow mask to differentiate the beams

31. 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…

32. 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.

33. 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

34. 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

35. Active Matrix LCDs Pros and Cons
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

36. 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

37. Plasma Display Panel Pros and Cons
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

38. Display Technology: DMDs
Digital Micromirror Devices (projectors)
Microelectromechanical (MEM) devices, fabricated with VLSI techniques

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

40. 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

41. 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

42. Organic LED Arrays Pros and Cons
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

43. Traditional Input Device (1/4)
Commonly used today
Mouse-like devices
mouse
wheel mouse
trackball
Keyboards

44. 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™

45. Traditional Input Device (3/4)
Joysticks
game pads
flightsticks
Touchscreens
Microphones
wireless vs. wired
headset

46. Traditional Input Device (4/4)
Digital still and video cameras, scanners
MIDI devices
input from electronic musical instruments
more convenient than entering scores with just a mouse/keyboard

47. 3D Input Device (1/2) Electromagnetic trackers
can be attached to any head, hands, joints, objects
Polhemus FASTRAK™(used in Brown’s Cave)
Acoustic-inertial trackers
Intersense IS-900

48. 3D Input Device (2/2) Gloves Pinch gloves
attach electromagnetic tracker to the hand
Pinch gloves
contact between digits is a “pinch” gesture
in CAVE, extended Fakespace PINCH™ gloves with extra contacts

49. Video Output Devices (1/4)
Classification
Stereo
head-mounted displays
shutter glasses
Degree of immersion
conventional desktop screen
walkup VR, semi-immersive displays immersive virtual reality

50. Video Output Devices (2/4)
Example of Immersive
Display
Diffusion Tensor MRI Brain Visualization at Brown University

51. Video Output Devices (3/4)
Desktop
Vector display
CRT
LCD flatpanel
workstation displays(Sun Lab)
PC and Mac laptops
Tablet computers
Wacom’s display tablet

52. Video Output Devices (4/4)
Immersive
Head-mounted displays (HMD)
Stereo shutter glasses
Virtual Retinal Display (VRD)
CAVE™

53. 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 Mouse Light pen Joystick Button devices Dials and levers 3D locators Touch panels Voice Input Scanners

54. Hard Copy Devices Printers Plotters
Non-Impact printers --- Ink jet; laser;
Xerographic;
Electrostatic;
Dye sublimation.
Plotters
Flatbed, Beltbed
Multiple pens available
Plotter `languages’
Built in character sets, line styles etc.

55. 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.

56. Raster Scan Display Systems
The various hardware architectures for providing graphics functionality differ on two axes
Processing performed by specialized graphics hardware.
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

57. 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.

58. Simple Raster systems (1/2)
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.

59. Simple Raster systems (2/2)
Dual ported frame buffer:
Frame buffer in special, dual ported Video RAM.
Unloads bus.
More expensive.
Less exible.

60. Systems with video processors (1/3)
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.

61. 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.

62. Systems with video processors (3/3)
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.

63. Example: Voodoo Voodoo chipset manufactured by 3Dfx, Inc.
3D-only graphics chipset.
Card manufacturers would build cards around Voodoo chip
Came out in probably first consumer-level 3D accelerator.
Combined hardware (Voodoo chip) and software (Direct3D/OpenGL/Glide) solution.

64. 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.

65. 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.

66. 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).

67. 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.
Some very nice white papers on T & L and cube enviromapping.

68. 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.

69. Render farms Closely related to Beowulf clusters
Idea: Use many tightly-coupled 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.