Question
How is an interlaced scanning pattern generated in a fast-scan (NTSC) television system?
Answer Options
- A) By scanning two fields simultaneously
- B) By scanning each field from bottom-to-top
- C) By scanning lines from left-to-right in one field and right-to-left in the next
- D) By scanning odd-numbered lines in one field and even-numbered lines in the next
Correct Answer: D
Explanation
Interlaced scanning is a technique used in the analog NTSC standard to reduce the required bandwidth while maintaining the perception of fluid motion and high resolution. Instead of transmitting and displaying all 525 lines of a frame sequentially (which would require a higher flicker rate or a wider bandwidth), the system displays the image in two separate steps, or fields.
An interlaced scanning pattern is generated by scanning odd-numbered lines in one field and even-numbered lines in the next. The electron beam starts in the upper left corner and scans all the odd lines (Field 1); it then returns to the upper left and scans all the even lines (Field 2) in the time it takes to scan the first field. The viewer’s persistence of vision blends the two fields into one complete frame.
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