Graphics Device System

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, c

haracters, 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 (8.5”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

10

Aspect Ratio

Frame aspect ratio (FAR) = horizontal/vertical sizeTV 4:3HDTV 16:9Page 8.5:11 ~ 3/435mm 3:2Panavision 2.35:1 (2:1 anamorphic)Vistavision 2.35:1 (1.5 anamorphic)

Pixel aspect ratio (PAR) = FAR vres/hresNuisance 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

1/60 SEC

1/30 SEC

1/60 SEC

FIELD 1 FIELD 2

FRAME

1/60 SEC

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 colors24bits/pixel -> 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

Green

Red

Blue

8

8

8

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

127 127

0

255

2083 00000000 00000100 00010011

to blue gun

to green gun

to red gunx

y

18

Pseudo Color

0

1

2

3

254

255

RED GREEN BLUE

256 colors chosen from a palette of 16,777,216.

Each entry in the color map LUT can be user defined.

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 (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), wh

ereas 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 p

ut 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


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 seemto be active-matrix

More on Displayhttp://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 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

Pen-based devices pressure sensitive absolute positioning tablet computers

IPAQ, WinCE machines Microsoft eTablet

coming soon palm-top devices

Handspring Visor, PalmOS™


45


Joysticks game pads flightsticks Touchscreens

Microphones wireless vs. wired headset

46


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

http://www.polhemus.com/ftrakds.htm http://www.isense.com/products/prec/is900/index.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-equips/hmd.html

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

50


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


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

52


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

53

Interactive Input Devices

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

Other deviceGraphics tablet MouseLight pen JoystickButton devices Dials and levers3D locators Touch panelsVoice Input Scanners

KeyboardMay be customized to application. Can include dials, joysticks.

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 whi

ch adjacent black and white lines can be distinguished. Many devices work by producing (colored) dots, and im

age 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 hardwar

e. Simplest has only video controller. More complex systems use a graphics display processor with

varying functionality. Relationship of frame buffer to CPU memory architectu

re. 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 conges

tion.

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 (23/ )

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 (33/ )

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.

Graphics Device System

Documents

Transcript of Graphics Device System