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RASTER & RANDOM SCAN
DISPLAYS
Raster Scan Display
• Electron Beam – Swept Across Screen –Top to Bottom –One
at Time
• Beam moves – Each Row – Intensity ...
• Horizontal Retrace: Beam Return - left screen
– after refreshing each scan line.
• Vertical Retrace: End of Frame - Beam...
RASTER SCAN DISPLAY
Advantages of raster scan:
 Decrease memory costs
 High degree realism is achieved in picture advanced shading & hidden ...
 Lines produced are zigzag as the plotted values are
discrete.
 Resolution is low.
Random Scan Display
• Electron Beam – Directly – Part of the screen
• Vector Display/Stroke Writing/Calligraphic Display:
...
• Refresh Buffer: Picture Definition –Stored –
Set of line drawing –Memory area
• Draw – Line in picture – 30-60 times a
s...
RANDOM SCAN DISPLAY
Advantages of random scan:
 Very high resolution, limited only by
monitor.
 Easy animation, just draw at different
posit...
 Requires “intelligent electron beam, i.e., processor controlled.
 Limited screen density before have flicker, can’t dra...
DIFFERENCE B/W RASTER & RANDOM SCAN
SYSTEM
Random Scan System

Raster Scan System

Cannot draw realistic shaded scenes.

U...
DIFFERENCE B/W RASTER & RANDOM SCAN
SYSTEM
Random Scan System

Raster Scan System

Cannot Produce Contrast , memory
doesnt...
Cathode ray tube
• Cathode Ray Tube (CRT) – Vacuum Tube – Contains
 Electron gun (a source of electrons)
 Filament (copp...
Cathode Ray Tube
Electron gun
CATHODE RAY TUBE
Properties of CRT
Phosphoresce

Electron Beam Strikes - Glows

Fluorescence

Ability of Phosphoresce glow after beam is sh...
BEAM PENETRATION

• Used in Random Scan Displays
• Colors Depends on the speed of the beam
• 2 phosphoresce layers : Red &...
SHADOW MASK
• Used - raster-scan systems (Color
TV)
• Produce - wider range of color than
beam penetration method
• 3 phos...
THANK YOU
Random and raster scan
Random and raster scan
Random and raster scan
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Random and raster scan

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Random and raster scan

  1. 1. RASTER & RANDOM SCAN DISPLAYS
  2. 2. Raster Scan Display • Electron Beam – Swept Across Screen –Top to Bottom –One at Time • Beam moves – Each Row – Intensity –Turned On/Off Create Pixels • Refresh/Frame Buffer: Information of picture stored – Memory Area • Pixels value retrieve – memory(buffer) – Plotted - Screen
  3. 3. • Horizontal Retrace: Beam Return - left screen – after refreshing each scan line. • Vertical Retrace: End of Frame - Beam Return – top left screen – begin next frame. • Example: TV Sets
  4. 4. RASTER SCAN DISPLAY
  5. 5. Advantages of raster scan:  Decrease memory costs  High degree realism is achieved in picture advanced shading & hidden surface technique.  Computer monitors and TVs use this method
  6. 6.  Lines produced are zigzag as the plotted values are discrete.  Resolution is low.
  7. 7. Random Scan Display • Electron Beam – Directly – Part of the screen • Vector Display/Stroke Writing/Calligraphic Display: Picture- Drawn – one at Time • Example: Pen Plotter • Refresh Rate –Depends - no. of line to be Displayed
  8. 8. • Refresh Buffer: Picture Definition –Stored – Set of line drawing –Memory area • Draw – Line in picture – 30-60 times a second
  9. 9. RANDOM SCAN DISPLAY
  10. 10. Advantages of random scan:  Very high resolution, limited only by monitor.  Easy animation, just draw at different position.  Requires little memory.
  11. 11.  Requires “intelligent electron beam, i.e., processor controlled.  Limited screen density before have flicker, can’t draw a complex image.  Limited color capability
  12. 12. DIFFERENCE B/W RASTER & RANDOM SCAN SYSTEM Random Scan System Raster Scan System Cannot draw realistic shaded scenes. Used in Systems to Display Realistic Images. Store - Line drawing instruction Store – Value related to pixels (Intensity value) Higher Resolution No Support – High Resolution Smooth line drawings Capable of Producing Curves Better
  13. 13. DIFFERENCE B/W RASTER & RANDOM SCAN SYSTEM Random Scan System Raster Scan System Cannot Produce Contrast , memory doesnt store intensity value of pixel Picture with better contrast Ex. Pen plotter Ex. TV sets Costlier Cost not too high as compared to Random Scan Line Drawing ,Known as Vector Display Mainly used for Point Plotting
  14. 14. Cathode ray tube • Cathode Ray Tube (CRT) – Vacuum Tube – Contains  Electron gun (a source of electrons)  Filament (copper grid)  Cathode (metal)  Control Grid (Positively charged)  Focusing Structure  Accelerating Anode  Deflection Coils  Screen (inside layer covered with phosphor)
  15. 15. Cathode Ray Tube
  16. 16. Electron gun
  17. 17. CATHODE RAY TUBE
  18. 18. Properties of CRT Phosphoresce Electron Beam Strikes - Glows Fluorescence Ability of Phosphoresce glow after beam is shut down Persistence Time duration –phosphoresce emit light – after turn off Aspect Ratio Resolution Refresh Rate Ratio – No. of vertical pixels – horizontal pixels - plotted Maximum No. of Pixels - plotted Frames – plotted again – seconds time
  19. 19. BEAM PENETRATION • Used in Random Scan Displays • Colors Depends on the speed of the beam • 2 phosphoresce layers : Red & Green • Not Expensive • Not Good Quality Picture • If Speed of Beam High Then Red Color is visible on screen
  20. 20. SHADOW MASK • Used - raster-scan systems (Color TV) • Produce - wider range of color than beam penetration method • 3 phosphor color dots at each pixel position. • Emits Red ,Green, Blue light • Expensive • No light Speed Criteria
  21. 21. THANK YOU

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