CG - Display Devices


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CG - Display Devices

  1. 1. Display DevicesOrganized By: Vinay Arora Assistant Professor, CSED Thapar University, Patiala
  2. 2. Disclaimer This is NOT A COPYRIGHT MATERIALContent has been taken mainly from the following books & websites: Computer Graphics C Version By Donald Hearn, M. Pauline BakerSchaums outline of theory and problems of computer graphics By Zhigang Xiang, Roy A. Plastock Computer Graphics: Principles and Practice By James D. Foley etc… Vinay Arora TU, CSED
  3. 3. Display Devices A Display Device is an Output device for presentation of Information for Visual reception. The Display Systems are often referred to as Video Monitor or Video Display Unit (VDU). Display Devices having CRT:- DVST – Direct View Storage Tube Random Scan Raster Scan Vinay Arora TU, CSED
  4. 4. Computer Monitor - External View Vinay Arora TU, CSED
  5. 5. Computer Monitor - Internal View Vinay Arora TU, CSED
  6. 6. CRT Vinay Arora TU, CSED
  7. 7. Electron Gun Vinay Arora TU, CSED
  8. 8. Electron Gun Heat is supplied to the cathode by the Filament. Vinay Arora TU, CSED
  9. 9. CRT - Operation of Electron Gun Vinay Arora TU, CSED
  10. 10. Positively Charged Metal (No Accelerating Anode) A positively charged metal coating on the inside of the CRT envelope near the phosphor screen. Vinay Arora TU, CSED
  11. 11. Electrostatic Deflection Vinay Arora TU, CSED
  12. 12. Magnetic Deflection Vinay Arora TU, CSED
  13. 13. Magnetic Coil Vinay Arora TU, CSED
  14. 14. CRT Vinay Arora TU, CSED
  15. 15. Brands of CRT Vinay Arora TU, CSED
  16. 16. Resolution Vinay Arora TU, CSED
  17. 17. Resolution Vinay Arora TU, CSED
  18. 18. Related Terms Fluorescence – Is the light emitted as electrons lose their excess energy while the Phosphor is being struck by electrons. Phosphorescence – Is the light given off by the return of the relatively more stable excited electrons to their unexcited state, once the electron beam excitation is removed. Persistence – Time from the removal of the excitation to the moment when Phosphorescence has decayed to 10% of the Initial Light Output. Vinay Arora TU, CSED
  19. 19. Raster Scan Display Raster Scan is the representation of images as a collection of pixels/dots (A Rectangular array of Points or Dots) Pixel: One Dot or Picture element of the Raster Scan Line: A Row of Pixels Vinay Arora TU, CSED
  20. 20. Raster Scan Display (contd.) In a Raster Scan System, the electron beam is swept across the screen, one row at a time from top to bottom. Vinay Arora TU, CSED
  21. 21. Raster Scan Display (contd.) Picture Definition is stored in a memory area called the Refresh Buffer or Frame Buffer. Refresh Buffer or Frame Buffer This memory area holds the set of intensity values for all the screen points. Stored Intensity values then retrieved from refresh buffer and “painted” on the screen one row (scan line) at a time. Vinay Arora TU, CSED
  22. 22. Raster Scan Display (contd.) Vinay Arora TU, CSED
  23. 23. Raster Drawing Vinay Arora TU, CSED
  24. 24. Architecture - Raster System In addition to the Central Processing Unit (CPU), a special processor, called the Video Controller or Display Controller, is used to control the operation of the Display Device. Vinay Arora TU, CSED
  25. 25. Architecture - Raster System (Conti…) A fixed area of the system memory is reserved for the frame buffer, and the video controller is given direct access to the frame buffer memory. Vinay Arora TU, CSED
  26. 26. Pixel Coordinate System In a Pixel Coordinate System the Pixel at the Lower Left corner of an image is considered to be at the origin (0,0). Vinay Arora TU, CSED
  27. 27. Cartesian Coordinates Screen Positions, are referenced in Cartesian Coordinates. Scan Lines are then labeled from ymax at the top of the screen to 0 at the bottom. Along each scan line, screen pixel positions are labeled from 0 to xmax. Vinay Arora TU, CSED
  28. 28. Registers for Storing Coordinates Vinay Arora TU, CSED
  29. 29. Random Scan Display In a Random Scan Display, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Random Scan monitors draw a picture One Line at a time (Vector Display, Stroke – Writing or Calligraphic Displays). Refresh rate depends on the number of lines to be displayed. Picture Definition is now stored as a Line-Drawing Commands an area of memory referred to as refresh display file (display list). To Display a Picture, the system cycle through the set of commands in the display file, drawing each component line in turn. Vinay Arora TU, CSED
  30. 30. Random Scan Display The component lines of a picture can be drawn and refreshed. Vinay Arora TU, CSED
  31. 31. Random Scan Drawing Vinay Arora TU, CSED
  32. 32. Architecture - Random System Vinay Arora TU, CSED
  33. 33. Random Scan Display Random Scan Displays are designed to draw all the component lines of a picture 30 to 60 times each second. Vinay Arora TU, CSED
  34. 34. Vector Drawing Vinay Arora TU, CSED
  35. 35. Random Scan Drawing Random scan displays are designed for line drawing applications and can not display realistic shaded scenes. Vinay Arora TU, CSED
  36. 36. View of Raster/Random Vinay Arora TU, CSED
  37. 37. Bitmap / Pixmap A Black-and-White System: Each Screen Point is either ON or OFF, so only one bit per pixel is needed to control the intensity of screen positions. On a Black-and-White System with one bit per pixel, the Frame Buffer is called BITMAP. For system with multiple bits per pixel, the Frame Buffer is called PIXMAP. Sometimes, refresh rates are described in unit of cycles per second, or Hertz (HZ) Vinay Arora TU, CSED
  38. 38. Color CRT Monitors A CRT monitor displays color pictures by using a combination of phosphors that emit different COLOR lights. Methods:- 1. Beam Penetration 2. Shadow Mask Vinay Arora TU, CSED
  39. 39. Beam Penetration Method Used with Random Scan monitors. Two layers of phosphor (red and green) are coated onto the inside of the CRT screen. The display color depends on how far the electron beam penetrates into the phosphor layers. The speed of the electrons, and the screen color at any point, is controlled by the beam acceleration voltage. Vinay Arora TU, CSED
  40. 40. Beam Penetration Method (contd.) Only 4 colors are possible (red, green, orange, and yellow). Quality of pictures is not as good as with other methods. Vinay Arora TU, CSED
  41. 41. Shadow Mask Method The color CRT has:- Three color phosphor dots (red, green and blue) at each point on the screen. Three electron guns, each controlling the display of red, green and blue light. 2 Methods for Implementation:- 1. Delta Method. 2. Inline Method. Vinay Arora TU, CSED
  42. 42. Shadow Mask Method (contd.) Used in raster scan system (including color TV) We obtain color variations by varying the intensity levels of the three electron beam. Designed as RGB monitors. High quality raster graphics system have 24 bits per pixel in the frame buffer (a Full Color System or a True Color System) Vinay Arora TU, CSED
  43. 43. Shadow Mask – Delta Method Vinay Arora TU, CSED
  44. 44. Delta Method Vinay Arora TU, CSED
  45. 45. Shadow Mask – Inline Method Vinay Arora TU, CSED
  46. 46. In Line Method Vinay Arora TU, CSED
  47. 47. Dot Pitch Vinay Arora TU, CSED
  48. 48. Flat Panel Displays A class of video devices that have reduce volume and weight compared to a CRT. A significant feature of Flat Panel Displays is that they are thinner than CRTs. Current uses for Flat Panel Displays: Small TV monitors Calculators Pocket video games Laptop computers Advertisement board in elevators Vinay Arora TU, CSED
  49. 49. Flat CRT Electron beams are accelerated parallel to the screen, then deflected 90º to the screen. Vinay Arora TU, CSED
  50. 50. Plasma Panel A layer of gas (usually neon) is sandwiched between two glass plates. Vinay Arora TU, CSED
  51. 51. Plasma Panel (Conti…) Vinay Arora TU, CSED
  52. 52. Plasma Panel (Conti…) By applying high voltage to a pair of horizontal & vertical conductors, a small section of the gas at the intersection of the conductors break down into glowing plasma of electrons and ions. Vinay Arora TU, CSED
  53. 53. Thin Film Electroluminescent The region between the glass plates is filled with a phosphor, such as zinc sulfide doped with manganese. Vinay Arora TU, CSED
  54. 54. Light Emitting Diode (LED) A matrix of diodes is arranged to form the pixel positions in the display, and picture definition is stored in a refresh buffer. Information is read from the refreshed buffer and converted to voltage levels that are applied to the diodes to produce the light patterns in the display. Vinay Arora TU, CSED
  55. 55. Liquid Crystal Displays (LCD) Used in small systems, such as calculators, laptop computers. Produce a picture by passing polarized light (from the surrounding or from an internal light source) through a liquid-crystal material that can be aligned to either block or transmit the light. Two glass plates, each containing a light polarizer at right angles to the other plate, sandwich the liquid crystal materials. Rows of horizontal transparent conductor & columns of vertical conductors (put into glass plates) Vinay Arora TU, CSED
  56. 56. LCD Display Vinay Arora TU, CSED
  57. 57. Off State To turn off the pixel, we apply a voltage to the two intersecting conductor to align the molecules so that the light is not twisted. Vinay Arora TU, CSED
  58. 58. On State Polarized light passing through the material is twisted so that it will pass through the opposite polarizer. Vinay Arora TU, CSED
  59. 59. Vinay AroraTU, CSED
  60. 60. Color Model Vinay Arora TU, CSED
  61. 61. The RGB Color Model R, G, and B represent the colors produced by red, green and blue phosphors, respectively. Vinay Arora TU, CSED
  62. 62. Color Depth, Bit Depth The number of discrete intensities that the video card is capable of generating for each color determines the maximum number of colors that can be displayed. The Number of Memory Bits required to store color information (intensity values for all three primary color components) about a pixel is called COLOR DEPTH or BIT DEPTH. A minimum of one memory bit (color depth=1) is required to store intensity value either 0 or 1 for every screen pixel. If there are n pixels in an image a total of n bits memory used for storing intensity values (in a pure black & white image) Vinay Arora TU, CSED
  63. 63. Bit Plane The block of memory which stores (or is mapped with) intensity values for each pixel (B& W image) is called a Bit Plane or Bitmap. Vinay Arora TU, CSED
  64. 64. 3 Bit Color Display Color or gray levels can be achieved in the display using additional bit planes. Vinay Arora TU, CSED
  65. 65. N Bit Planes & True Color The result for n bits per pixel (color depth=n) is a collection of n bit planes (2n colors or gray shades at every pixel) For TRUE COLOR three bytes of information are used, one for each of the red, blue and green signals that make a pixel. A byte can hold 256 different values and so 256 intensities setting are possible for each electron gun which mean each primary color can have 256 intensities (256*256*256 color possible) Vinay Arora TU, CSED
  66. 66. True Color Vinay Arora TU, CSED
  67. 67. Frame Buffer Vinay Arora TU, CSED
  68. 68. Look Up Table (LUT) Vinay Arora TU, CSED
  69. 69. Frame Buffer with LUT Vinay Arora TU, CSED
  70. 70. Frame Buffer with LUT (Conti…) Vinay Arora TU, CSED
  71. 71. General Terms Modeling Coordinates World Coordinates Device Coordinates Geometric Transformations Viewing Transformations GKS (Graphics Kernel System) PHIGS/PHIGS+ (Programmer’s Hierarchical Interactive Graphics Standard) Vinay Arora TU, CSED
  72. 72. Transformation Sequence Vinay Arora TU, CSED
  73. 73. Horizontal/Vertical Retrace Horizontal Retrace: The return to the left of the screen, after refreshing each scan line. Vertical Retrace: At the end of each frame the electron beam returns to the top left corner of the screen to begin/start again. Vinay Arora TU, CSED
  74. 74. Interlacing On some raster systems (TV), each frame is displays in two passes using an interlaced refresh procedure. Vinay Arora TU, CSED
  75. 75. Interlacing - Example Vinay Arora TU, CSED
  76. 76. Aspect Ratio The ASPECT RATIO of an image is the ratio of the width of the image to its height, measured in Unit length or number of pixels. e.g. 2 x 2 inch image and a 512 x 512 image would have an Aspect ratio of 1 Vinay Arora TU, CSED
  77. 77. Resolution Can be defined as the Number of Pixels per unit Length. Normally Image Size is given as Total Number of pixels in Horizontal direction times the Total number of pixels in Vertical direction. e.g. 512 x 512, 1024 x 768 etc. Vinay Arora TU, CSED
  78. 78. Thnx… Vinay Arora TU, CSED