Graphics Device System

1
Graphics Device System

• Pradondet Nilagupta
• Dept. of Computer Engineering
• Kasetsart University

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
• NTSC 640x480x8b 1/4 MB
• GA-HDTV 1920x1080x8b 2 MB
• Workstations
• Bitmapped display 960x1152x1b 1 Mb
• Color workstation 1280x1024x24b 5 MB
• Laserprinters
• 300 dpi (8.5x300)(11x300) 1.05 MB
• 2400 dpi (8.5x2400)(11x2400) 64 MB
• Film (line pairs/mm)
• 35mm (diagonal) slide (ASA25125 lp/mm) 3000
• 3000 x 2000 x 3 x 12b 27 MB

10
Aspect Ratio

• Frame aspect ratio (FAR) horizontal/vertical
  size
• TV 43
• HDTV 169
• Page 8.511 3/4
• 35mm 32
• Panavision 2.351 (21
  anamorphic)
• Vistavision 2.351 (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
  fieldsone 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.

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 -gt 256
simultaneous colors24bits/pixel -gt 16 million
simultaneous colors
15
Specifying Color

• 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
18
Pseudo Color
19
Cathode Ray tube
20
Display Technology

• 2D 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 (lastof 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
• Show http//graphics.lcs.mit.edu/classes/6.837/F9
  8/Lecture1/Slide11.html
• Name two disadvantages
• Just does wireframe
• Display needs constant update to avoid fading

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. Its a hack. Why do
  it?
• 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. 1000 line plot vector disply computes 2000
  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
http//www.udayton.edu/cps/cps460/notes/displays/
30
Display Technology Color CRTs

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

http//www.udayton.edu/cps/cps460/notes/displays/
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.

http//www.udayton.edu/cps/cps460/notes/displays/
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

http//www.udayton.edu/cps/cps460/notes/displays/
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 seemto be active-matrix

More on Display http//www.udayton.edu/cps/cps460
/notes/displays/
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

• 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

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
  processnot 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 (lt 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 Browns Cave)
• Acoustic-inertial trackers
• Intersense IS-900

http//www.isense.com/products/prec/is900/index.ht
m
http//www.polhemus.com/ftrakds.htm
48
3D Input Device (2/2)

• 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

http//www.fakespacelabs.com/products/pinch.html
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

http//robotics.aist-nara.ac.jp/equipments/E-equip
s/hmd.html
http//www.virtualresearch.com/index.html
50
Video Output Devices (2/4)

• Example of Immersive
• Display
• Diffusion Tensor MRI Brain Visualization at Brown
  University

http//www.cs.brown.edu/research/graphics/research
/sciviz/brain/brain.html
51
Video Output Devices (3/4)

• Desktop
• Vector display
• CRT
• LCD flatpanel
• workstation displays(Sun Lab)
• PC and Mac laptops
• Tablet computers
• Wacoms display tablet

http//www.wacom.com/productinfo/index.cfm
52
Video Output Devices (4/4)

• Immersive
• Head-mounted displays (HMD)
• Stereo shutter glasses
• Virtual Retinal Display (VRD)
• CAVE

http//www.evl.uic.edu/research/template_res_proje
ct.php3?indi27
53
Interactive Input Devices

• A graphics work station commonly has one or two
  monitors and a range of input devices. These can
  include

KeyboardMay 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
• 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 1996 ... 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.
• http//www.nvidia.com. 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.