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 for most CRT computer monitors. (Other CRT-type displays, such as televisions, typically use interlacing.) 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 1.6. 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
Not all HDTVs allow progressive scan as some HDTVs, such as 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.
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