Display Systems

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Display Systems

  1. 1. DISPLAY SYSTEMS
  2. 2. RASTER SCAN SYSTEMS • Interactive raster graphics employ several processing units • Apart from CPU, a special purpose processor called video controller or display controller  control operation of the display device • Simple raster graphics system
  3. 3. VIDEO CONTROLLER • Fixed area of system memory reserved for frame buffer • Video controller given direct access to frame buffer to refresh the screen • Coordinate origin is defined at lower left corner • Scan lines labeled from ymax at the top of the screen to 0 at the bottom
  4. 4. BASIC REFRESH OPERATIONS • Registers store the Horizontal and Raster Scan Vertical Deflection Generator Voltages coordinates of the screen pixels X Register Y Register • X  0; Y  ymax • Value stored in frame Memory Pixel Intensity buffer is used to set Address Register the intensity of the CRT Frame Buffer
  5. 5. • X incremented by 1; process repeated for each pixel along the scan line • Procedure is repeated for each scan line • After cycling through all pixels, refresh process starts over • To speed up processing, multiple pixel intensities are retrieved • Stored in separate register to control the CRT for group of adjacent pixels
  6. 6. • In high quality systems, two frame buffers are provided • One used for refreshing and other is filled with intensity values • Thus provides a fast mechanism for real time animation – different views successively loaded into refresh buffers
  7. 7. RASTER SCAN DISPLAY PROCESSOR Display processor Frame Video Monitor Memory Buffer Controller CPU Display System Processor Memory System bus
  8. 8. RASTER SCAN DISPLAY PROCESSOR • Separate display processor free CPU from graphics chores • Separate display processor memory also provided • Major task  digitizing picture definition into set of pixel intensities : scan conversion
  9. 9. • Display processor perform additional operations like generating various line styles, displaying various color areas and performing certain manipulations • To reduce memory requirements  Run length encoding : Store each scan line as a set of integer  Cell encoding : Encode as a set of rectangular areas
  10. 10. RANDOM SCAN SYSTEMS • Organization • Application program is input and stored in system memory along with the graphics package • Graphics commands in the application pgm is translated by graphics package into a display file which is accessed by display processor • Display processor  DPU or graphics controller
  11. 11. SIMPLE RASTER SYSTEM System Video CPU Monitor Memory Controller System Bus I/O Devices BACK
  12. 12. COMMON ORGANIZATION FOR RASTER SYSTEMS System Frame Video CPU Monitor Memory Buffer Controller System Bus I/O Devices BACK
  13. 13. RANDOM SCAN SYSTEMS System Display CPU Monitor Memory Processor System Bus I/O Devices BACK

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