Cg Chap 02


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Cg Chap 02

  1. 1. Chapter-2 Overview of Graphics Systems
  2. 2. Video Display Devices <ul><li>Raster scan </li></ul><ul><li>Random scan </li></ul><ul><li>D.V.S.T </li></ul><ul><li>Laser scan </li></ul><ul><li>Flat-panel displays (Plasma panel) </li></ul><ul><li>C.R.T </li></ul>Beam penetration Shadow mask
  3. 4. electron gun phosphor coated screen heating filament cathode control grid focusing anode accelerating anode Horizontal deflection plates vertical deflection plates CRT
  4. 5. Refresh Cathode-Ray Tube * The time taken by the emitted light to decay to 1 / 10 th its original intensity. <ul><li> Persistence: </li></ul>* Low persistence is useful for animation. <ul><li> Resolution: </li></ul>The number of pixels that can be plotted without overlap over a square unit area. Positively charged phosphor coated metal cylinder. <ul><li>Focusing system( electron gun ). </li></ul><ul><li>Deflection system. </li></ul>* Electric * Magnetic * Heating filament * Cathode * Control grid (or)
  5. 6. Beam penetration method <ul><li>Two layers of phosphor is used : </li></ul>Red and Green <ul><li>The displayed color depends on how far </li></ul><ul><li>the electron beam penetrates into the </li></ul><ul><li>phosphor layers. </li></ul><ul><li>Only 4 colors are possible. </li></ul>Red , Green , Orange , Yellow
  6. 7. Red Orange Green Yellow Beam penetration method
  7. 8. <ul><li>  Three phosphor color dots </li></ul><ul><li>at each pixel position. </li></ul><ul><li>  Three electron guns. </li></ul><ul><li>  Color variations: </li></ul><ul><li> varying the intensity levels of </li></ul><ul><li>the three electron beams. </li></ul><ul><li>  24 bits of storage per pixel. </li></ul><ul><li>  arrangements : </li></ul>* in - line method * delta - delta method Shadow Mask method
  8. 9. COLOUR GUNS Screen Shadow mask Delta-Delta method Phosphor dot triangle
  9. 10. COLOUR GUNS Screen Shadow mask In-line method
  10. 12. Raster Display Technology <ul><li>The graphics screen is a two-dimensional array of picture elements (‘pixels’) </li></ul><ul><li>Each pixel’s color is an individually programmable mix of red, green, and blue </li></ul><ul><li>These pixels are redrawn sequentially, left-to-right, by rows from top to bottom </li></ul>
  11. 13. Architecture of simple Raster graphics system CPU System Memory System Bus I/O devices Video controller Monitor Frame buffer A fixed area of system memory reserved for frame buffer
  12. 14. Raster Scan Memory Requirements  Interlacing * Even lines first * Odd lines next * 50 Hz to avoid flicker Memory Requirements depends on * resolution * colors, the system supports ex: For a resolution of 1024 * 768 Resolution with 8-bits per pixel( 256 colors ), it needs 768 Kb of memory.
  13. 15. Raster-Scan display processor CPU System Memory System Bus I/O devices Display processor memory Frame Buffer Video controller Display processor Monitor
  14. 16. Raster Scan Display processor <ul><li> Display processor / Graphics controller </li></ul><ul><li> To free the cpu from graphics chores </li></ul><ul><li>Scan conversion :Digitize a picture definition </li></ul><ul><li>into a set of pixel intensity values. </li></ul><ul><li> Display processor functions. </li></ul>* Generating various line styles. * Displaying color areas. * Performs certain transformations. * Manipulations on display objects. <ul><li> Run-length encoding.  </li></ul>* Reduce memory requirements. * Organize the frame buffer as a linked list. * Stores a scan line as a set of integer pairs. ( Intensity , number of adjacent pixels with that intensity ).
  15. 17. Raster Scan Generator X Register Y Register Memory Address Frame Buffer Pixel Register Horizontal and vertical deflection voltages Intensity Video controller addr (x,y) = base address + (x max – x min )(y – y min ) + ( x – x min )
  16. 18. Video controller  Co- ordinate system  Frame buffer locations are referenced in Cartesian co-ordinates.  Co-ordinate origin * Lower left screen corner. * Upper left screen corner.  Refresh operations of video controller  Top-to-bottom , Left-to-Right  X register(initial value = 0).  Y register (initial value = y max )
  17. 19. scan line Horizontal retrace Vertical retrace RASTER SCAN
  18. 20. Frame Buffers Rotating Memory Shift Register Multiple Plane
  19. 21. 1 1-bit register black and white display 1 Digital-to-Analog converter Frame buffer screen
  20. 22. 2-bit register black , white - gray color display Digital-to-Analog converter Frame buffer screen 1 1 1 1
  21. 23. Frame buffer Digital to Analog converters 1-bit registers simple color graphics display COLOUR GUNS screen 1 0 1 1 1 0 RED GREEN BLUE
  22. 24. Frame buffer screen multi color grpahics display 3-bit registers COLOUR GUNS Digital to Analog converters RED GREEN BLUE 1 0 0 0 1 1 1 1 0
  23. 25. Frame buffer screen multi color grpahics display (Look-up tables) 3-bit registers COLOUR GUNS W-bit Digital to Analog converters W-bit Look-up table 2 n entries RED GREEN BLUE 1 0 1 0 1 1 0 1 0
  24. 26. <ul><li>Frame Buffer / Refresh Buffer </li></ul><ul><li>Scan conversion </li></ul><ul><li>Pixel or pel </li></ul><ul><li>Scan line </li></ul><ul><li>bitmap , pixmap </li></ul><ul><li>Refreshing (60-80 frames/sec) </li></ul><ul><li>Horizontal retrace </li></ul><ul><li>vertical retrace </li></ul><ul><li>Interlacing </li></ul><ul><li>Flickering </li></ul><ul><li>Aspect Ratio </li></ul><ul><li>Stair step / jig-jag effect </li></ul>
  25. 28. Random scan system CPU System Memory System Bus I/O devices Display processor Monitor Graphics commands are translated into a display file stored in the system memory.
  26. 29. RANDOM SCAN
  27. 30. Random-Scan display <ul><li> Vector / Stroke-Writing / Calligraphic . </li></ul><ul><li> Picture definition is stored as a set of line </li></ul><ul><li>drawing commands called display file . </li></ul><ul><li> Draw a picture one line at a time. </li></ul><ul><li> Refresh rate depends on the number of </li></ul><ul><li>lines to be displayed. </li></ul><ul><li> Designed for line drawing applications. </li></ul><ul><li> Electron beam directly draws the picture. </li></ul>
  28. 31. + very high resolution. + Easy animation. + Little memory requirements. - Can’t draw a complex image (flicker) . - Limited colour capability. - Very expensive.
  29. 32. flood gun writing gun writing beam electrons screen storage grid collector DVST
  30. 33. Direct-View storage tube <ul><li> Store the picture information inside the </li></ul><ul><li>CRT as a charge distribution just behind </li></ul><ul><li>the phosphor coated screen. </li></ul><ul><li> There exist two electron guns. </li></ul><ul><li> Primary gun. </li></ul><ul><li> Flood gun. </li></ul>+ Very complex pictures can be displayed at very high resolutions. - Do not display color. - Selected parts of the picture cannot be erased.
  31. 34. Flat-panel displays <ul><li> Video devices have reduced </li></ul><ul><li>* volume </li></ul><ul><li>* weight </li></ul><ul><li>* Power requirements </li></ul><ul><li>compared to CRT. </li></ul><ul><li> A significant feature is thinner than CRT. </li></ul><ul><li> Classified into 2 categories </li></ul> Emissive displays.  Non Emissive displays.
  32. 35. Emissive displays <ul><li> Convert electrical energy into light. </li></ul><ul><ul><li>Plasma panels. </li></ul></ul><ul><ul><li>Thin-film electroluminescent displays </li></ul></ul><ul><ul><li>light emitting diodes </li></ul></ul>Non Emissive displays <ul><li> Convert sunlight or other into graphic patterns. </li></ul><ul><ul><li>L iquid C rystal D isplays( LCD ). </li></ul></ul><ul><ul><ul><li>Calculators, portable,laptop computers </li></ul></ul></ul>Produce a picture by passing polarized light from the surroundings or from an internal light source through liquid-crystal that can be aligned to either block or transmit the light.
  33. 36. Neon gas plasma panel
  34. 37. polarizer polarizer Transparent conductor Transparent conductor On State Nematic Liquid Crystal Liquid Crystal Display
  35. 38. polarizer polarizer Transparent conductor Transparent conductor Off State Nematic Liquid Crystal Liquid Crystal Display
  36. 39. <ul><ul><ul><ul><li>Keyboard </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Mouse </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Joystick </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Digitising Tablet </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Touch Sensitive Screen </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Light Pen </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Space Mouse </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Digital Stills Camera </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Magnetic Ink CharacterRecognition (MICR) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Optical Mark Reader(OMR) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Image Scanner </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Bar Codes </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Magnetic Reader </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Smart Cards </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Voice Data Entry </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sound Capture </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Video Capture </li></ul></ul></ul></ul>
  37. 54. Output Devices Hard copy Printers Plotters Storage Refresh Raster Random Screen D.V.S.T Flat panel display Laser scan L.C.D Soft copy
  38. 55. Element Dot matrix Line Inkjet Printers impact non impact Laser printers
  39. 56. Flat bed Drum Plotters
  40. 57. Co - ordinate Representations <ul><li>Modeling Co-ordinates: (X mc ,Y mc ,Z mc ) </li></ul><ul><li>World Co-ordinates: (X wc ,Y wc ,Z wc ) </li></ul><ul><li>Normalized Co-ordinates: (X nc ,Y nc ,Z nc ) </li></ul><ul><li>Device Co-ordinates: (X dc ,Y dc ,Z dc ) </li></ul>* Any floating point values * Any floating point values * Integers within the range (0,0) to (X max , Y max ). * 0 <= X nc <= 1, 0 <= Y nc <= 1, 0 <= Z nc <= 1.
  41. 58. Co-ordinate Representations 1 1 1 Modeling co-ordinates World co-ordinates Normalized co-ordinates
  42. 59. Graphics software standards <ul><li>GKS :- Graphics Kernel System </li></ul><ul><li>PHIGS :- Programmer’s Hierarchical </li></ul><ul><li>Interactive Graphics Standard </li></ul>
  43. 60. The End
  44. 61. laser modulator focusing lense x-y deflectors photochromic film light source screen stored picture beam refresh beam projection light LASER SCAN
  45. 62. Run-Length Encoding (RLE) <ul><li>A simple technique for ‘data-compression’ </li></ul><ul><li>Well-suited for compressing images, when adjacent pixels often have the same colors </li></ul><ul><li>Without compression, a computer graphics image-file (for SuperVGA) would be BIG! </li></ul><ul><li>Exact size depends on screen-resolution </li></ul><ul><li>Also depends on the display’s color-depth </li></ul><ul><li>(Those parameters are programmable) </li></ul>
  46. 63. How RLE-compression works <ul><li>If multiple consecutive bytes are identical: </li></ul><ul><li>example: 0x29 0x29 0x29 0x29 0x29 </li></ul><ul><li>(This is called a ‘run’ of five identical bytes) </li></ul><ul><li>We “compress” five bytes into two bytes: </li></ul><ul><li>the example compressed: 0xC5 0x29 </li></ul><ul><li>Byte-pairs are used to describe ‘runs’: </li></ul><ul><li>Initial byte encodes a ‘repetition-count’ </li></ul><ul><li>(The following byte is the actual data) </li></ul>