Progressive scan
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Progressive or noninterlaced 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.
The 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.
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[edit] Usage in storing or transmitting
Progressive scan is used for scanning and storing film based material on DVDs, for example, as 480p24 or 576p25 formats. Used as image acquisition method also in every FireWire camera based on CCD sensor.
[edit] Advantages of progressive scan
- Simpler video processing equipment
- Easier compression
- Higher resolution and fewer artifacts in video with motion compared to interlaced video of the same line rate.
[edit] Usage in display
Progressive scan is used for most CRT computer monitors, as the source signal is progressive by nature (Other CRT-type displays, such as televisions, typically use interlaced displays). It is also becoming increasingly common in high-end television equipment, which is often capable of performing deinterlacing so that interlaced source video can still be viewed.
[edit] Advantages of progressive scan
- 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 means that, when viewing progressive sourced material, a progressive display will show a more detailed image, when compared to an interlaced one, even if both have exactly the same display resolution.
- No flickering of narrow horizontal patterns
- Simpler video processing equipment
[edit] Disadvantages of progressive scan
- Progressive scan will have half the frame rate of an interlaced scan's field rate, at a given line rate. This reduces motion smoothness, which may be a disadvantage in fast-changing images such as sports coverage. To maintain the same smoothness, double the line rate is required.
For a discussion of why interlacing was originally used, see Interlace.
