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Graphics Device System Pradondet Nilagupta Dept. of Computer Engineering Kasetsart University Graphical System 5 major elements for a computer graphic system Processor Memory Frame buffer Input devices Output Devices Output Technology (1/3) Calligraphic Displays

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graphics device system

Graphics Device System

Pradondet Nilagupta

Dept. of Computer Engineering

Kasetsart University

204481 Foundation of Computer Graphics

graphical system
Graphical System

5 major elements for a computer graphic system

  • Processor
  • Memory
  • Frame buffer
  • Input devices
  • Output Devices

204481 Foundation of Computer Graphics

output technology 1 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.

204481 Foundation of Computer Graphics

output technology 2 3
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

204481 Foundation of Computer Graphics

output technology cont
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.

204481 Foundation of Computer Graphics

pros and cons
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

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basic definitions
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.

204481 Foundation of Computer Graphics

resolution
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

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example
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 (8.5”x300)(11”x300) 1.05 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

204481 Foundation of Computer Graphics

aspect ratio
Aspect Ratio

Frame aspect ratio (FAR) = horizontal/vertical size

TV 4:3

HDTV 16:9

Page 8.5:11 ~ 3/4

35mm 3:2

Panavision 2.35:1 (2:1 anamorphic)

Vistavision 2.35:1 (1.5 anamorphic)

Pixel aspect ratio (PAR) = FAR vres/hres

Nuisance in graphics if not 1

204481 Foundation of Computer Graphics

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

204481 Foundation of Computer Graphics

refresh rates and bandwidth
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

204481 Foundation of Computer Graphics

interlaced scanning

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

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.

204481 Foundation of Computer Graphics

frame buffer
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 colors24bits/pixel ->16 million simultaneous colors

204481 Foundation of Computer Graphics

specifying color

8

8

8

Red

Blue

Green

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

204481 Foundation of Computer Graphics

lookup tables
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.

204481 Foundation of Computer Graphics

color look up table

CLUT

Frame Buffer

0

127

2083

y

00000000

00000100

00010011

to blue

gun

to red

gun

to green

gun

x

255

127

Color Look-Up Table

204481 Foundation of Computer Graphics

pseudo color
Pseudo Color

204481 Foundation of Computer Graphics

cathode ray tube
Cathode Ray tube

204481 Foundation of Computer Graphics

display technology
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)

204481 Foundation of Computer Graphics

display technologies
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

204481 Foundation of Computer Graphics

display technologies crts
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/F98/Lecture1/Slide11.html
    • Name two disadvantages
      • Just does wireframe
      • Display needs constant update to avoid fading

204481 Foundation of Computer Graphics

vector display architecture
Vector Display Architecture

204481 Foundation of Computer Graphics

display technologies crts24
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. 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.

204481 Foundation of Computer Graphics

raster displays architecture
Raster displays Architecture

204481 Foundation of Computer Graphics

raster refresh
Raster refresh

204481 Foundation of Computer Graphics

comparing raster and vector 1 2
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

204481 Foundation of Computer Graphics

comparing raster and vector 2 2
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

204481 Foundation of Computer Graphics

display technology color crts
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/

204481 Foundation of Computer Graphics

display technology color crts30
Display Technology: Color CRTs
  • Color CRTs have
    • Three electron guns
    • A metal shadow maskto differentiate the beams

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

204481 Foundation of Computer Graphics

display technology raster
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…

204481 Foundation of Computer Graphics

display technology lcds
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/

204481 Foundation of Computer Graphics

slide33
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/

204481 Foundation of Computer Graphics

active matrix lcds
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

204481 Foundation of Computer Graphics

active matrix lcds pros and cons
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/

204481 Foundation of Computer Graphics

plasma
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

204481 Foundation of Computer Graphics

plasma display panel pros and cons
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

204481 Foundation of Computer Graphics

display technology dmds
Display Technology: DMDs
  • Digital Micromirror Devices (projectors)
    • Microelectromechanical (MEM) devices, fabricated with VLSI techniques

204481 Foundation of Computer Graphics

dmds pros and cons
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

204481 Foundation of Computer Graphics

slide40
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

204481 Foundation of Computer Graphics

organic led arrays
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

204481 Foundation of Computer Graphics

organic led arrays pros and cons
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

204481 Foundation of Computer Graphics

traditional input device 1 4
Traditional Input Device (1/4)
  • Commonly used today
  • Mouse-like devices
    • mouse
    • wheel mouse
    • trackball
  • Keyboards

204481 Foundation of Computer Graphics

traditional input device 2 4
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™

204481 Foundation of Computer Graphics

traditional input device 3 4
Traditional Input Device (3/4)
  • Joysticks
    • game pads
    • flightsticks
    • Touchscreens
  • Microphones
    • wireless vs. wired
    • headset

204481 Foundation of Computer Graphics

traditional input device 4 4
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

204481 Foundation of Computer Graphics

3d input device 1 2
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

http://www.isense.com/products/prec/is900/index.htm

http://www.polhemus.com/ftrakds.htm

204481 Foundation of Computer Graphics

3d input device 2 2
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

204481 Foundation of Computer Graphics

video output devices 1 4
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-equips/hmd.html

http://www.virtualresearch.com/index.html

204481 Foundation of Computer Graphics

video output devices 2 4
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

204481 Foundation of Computer Graphics

video output devices 3 4
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

http://www.wacom.com/productinfo/index.cfm

204481 Foundation of Computer Graphics

video output devices 4 4
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_project.php3?indi=27

204481 Foundation of Computer Graphics

interactive input devices
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

204481 Foundation of Computer Graphics

hard copy devices
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.

204481 Foundation of Computer Graphics

hardcopy technologies
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.

204481 Foundation of Computer Graphics

raster scan display systems
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

204481 Foundation of Computer Graphics

video controller
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.

204481 Foundation of Computer Graphics

simple raster systems 1 2
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.

204481 Foundation of Computer Graphics

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

204481 Foundation of Computer Graphics

systems with video processors 1 3
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.

204481 Foundation of Computer Graphics

systems with video processors 2 3
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.

204481 Foundation of Computer Graphics

systems with video processors 3 3
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.

204481 Foundation of Computer Graphics

example voodoo
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.

204481 Foundation of Computer Graphics

voodoo hardware
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.

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example geforce 256
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.

204481 Foundation of Computer Graphics

hardware features 1 2
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).

204481 Foundation of Computer Graphics

hardware features 2 2
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.

204481 Foundation of Computer Graphics

geforce 3
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.

204481 Foundation of Computer Graphics

render farms
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.

204481 Foundation of Computer Graphics