Raster Scanning

• In cameras and displays, some time is required to advance the scanning operation to retrace from one line to the next and from one picture to the next. These intervals are called blanking intervals.
  • In conventional CRT display the electron beam must be extinguished (blanked) during these time intervals. The horizontal blanking time lies between scan lines, and vertical blanking lies between frames (or fields).
  • The raster structure of 525/59.94 and 625/50 digital video systems, including these blanking intervals. In analog video, sync information is conveyed during the blanking intervals.
  • The horizontal and vertical blanking intervals required for a CRT display are quite large fractions of the line time and frame time: in 525/59.94, 625/50, and 1920 × 1035 systems, vertical blanking occupies 8 percent of each frame period.
  • Although in principle a digital video interface could omit the blanking intervals and use a clock having a lower frequency than the sampling clock, this would be impractical.
  • Digital video standards use interface clock frequencies chosen to match the large blanking intervals of typical display equipment.
  • A digital video interface may convey audio signals during blanking; a digital video tape recorder might record error correction information in these intervals.

Diagram

Advantages of Raster Scan Display:

1. Can show Realistic pictures
2. Million unique hues can be produced
3. Shadow scenes are conceivable

Drawbacks of Raster Scan Display:

1. Low Resolution
2. Electron beam coordinated to whole screen not exclusively to those parts of the screen where picture is to be drawn so tedious when the drawn picture estimate is especially not as much as the whole screen.
3. Expensive