Progressive scan

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Progressive or non-interlaced scanning is any method for displaying, storing or transmitting moving images in which the lines of each frame are drawn in sequence. This is in contrast to the interlacing used in traditional television systems.

Progressive scan is used in most CRTs used as computer monitors. It is also becoming increasingly common in high-end television equipment, which is often capable of performing deinterlacing so that interlaced video can still be viewed.

Advantages of progressive scan include:

  • Subjectively increased vertical resolution. The perceived vertical resolution of an interlaced image is usually equivalent to multiplying the active lines by about 0.6. This explains, for example, why HDTV standards such as 1080i (1920x1080, interlaced) in most cases deliver a quality equal to or slightly poorer than that of 720p (1280x720, progressive), despite containing far more lines of resolution.
  • No flickering of narrow horizontal patterns
  • Simpler video processing equipment
  • Easier compression

Note: This system was originally known as 'sequential scanning' when it was used in the Baird 240 line television transmissions from Alexandra Palace, England in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920's.

Not all HDTV allow Progressive scan, as some HDTV like LG only offer NTSC instead of PAL (if your country is using the PAL system).

For a discussion of why interlacing was originally used, see Interlace.de:Vollbildverfahren fr:Balayage progressif ko:순차 주사 방식 zh:逐行扫描

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