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Short note: Raster scan display

Short answer

A raster scan display sweeps the electron beam row by row across the screen, using a frame buffer to store pixel intensities. The video controller reads and displays each pixel, refreshing 50–60 Hz. It supports realistic shading and colour but requires large memory and can produce jagged lines.

Write a short note on raster scan display.

A raster scan display shows a picture by sweeping the electron beam across the screen one row (scan line) at a time, from top to bottom, and turning the beam intensity on or off at each pixel according to the frame buffer.

 ->->->->->->->->->|   scan line 1
 <-- horizontal retrace
 ->->->->->->->->->|   scan line 2
   ...
 ^ vertical retrace back to top after last line

Working

  • The image is stored in the frame buffer as pixel intensity values (1 bit per pixel for monochrome, 8 to 24 bits for colour).
  • The video controller reads the frame buffer line by line and drives the beam intensity.
  • Screen is refreshed 50 to 60 times per second. The beam is off during horizontal and vertical retrace.
  • Scanning may be interlaced (odd lines, then even lines) to reduce flicker, or non-interlaced.

Features

  • Realistic images, shading, many colours and filled areas.
  • Refresh time is independent of picture complexity.
  • Needs large memory; lines appear jagged (aliasing).
  • Used in TV, monitors and most modern displays.

✓ Answer checked by Claude Opus 5.5 (high effort)

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