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, 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 (8.5”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 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

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. 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.

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. 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

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. 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

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

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