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Graphics Device System

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

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  1. Graphics Device System Pradondet Nilagupta Dept. of Computer Engineering Kasetsart University 204481 Foundation of Computer Graphics

  2. Graphical System 5 major elements for a computer graphic system • Processor • Memory • Frame buffer • Input devices • Output Devices 204481 Foundation of Computer Graphics

  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

  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 204481 Foundation of Computer Graphics

  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. 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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. 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  11. 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

  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 204481 Foundation of Computer Graphics

  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. 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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. 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  18. Pseudo Color 204481 Foundation of Computer Graphics

  19. Cathode Ray tube 204481 Foundation of Computer Graphics

  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) 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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/F98/Lecture1/Slide11.html • Name two disadvantages • Just does wireframe • Display needs constant update to avoid fading 204481 Foundation of Computer Graphics

  23. Vector Display Architecture 204481 Foundation of Computer Graphics

  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. 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

  25. Raster displays Architecture 204481 Foundation of Computer Graphics

  26. Raster refresh 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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/ 204481 Foundation of Computer Graphics

  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/ 204481 Foundation of Computer Graphics

  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… 204481 Foundation of Computer Graphics

  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/ 204481 Foundation of Computer Graphics

  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/ 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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/ 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  38. Display Technology: DMDs • Digital Micromirror Devices (projectors) • Microelectromechanical (MEM) devices, fabricated with VLSI techniques 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  43. Traditional Input Device (1/4) • Commonly used today • Mouse-like devices • mouse • wheel mouse • trackball • Keyboards 204481 Foundation of Computer Graphics

  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™ 204481 Foundation of Computer Graphics

  45. Traditional Input Device (3/4) • Joysticks • game pads • flightsticks • Touchscreens • Microphones • wireless vs. wired • headset 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

  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 204481 Foundation of Computer Graphics

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