Position:Video presentation has two kinds of basic kind: Interlaced scanning or progressive scanning. Progressive scanning, use on computer monitor and digital television, what show picture is all horizontal, as one frame. Interlaced scanning, use in standard NTSC, PAL, SECAM makes a television go up, show the half is horizontal only. (Field of the first scanning, include all and odd line, next field of the 2nd scanning, include all even wire) . The visual for the moment that interlaced scanning leans person eye takes character (this is mentally is caused, is not the) on physics, and the phosphorous of short duration on television kinescope stays make two scanning field becomes ambiguous, fashion an image that person eye finds. The advantage of interlaced scanning is to want original half data bulk to be able to achieve fast break rate only (50 or 60 Hz) . Defect is horizontal resolution reduces an in part essentially, because video passes filter wave normally,wait for other blemish with avoiding image to twinkle.
Considering image source is how to be caught conduce to the difference with both understanding. Per sec. of film pickup camera films 24 frame, and video pickup camera criterion every other 1/60 second scan odd line and even wire. (Projectile film is different, it shows for an instant whole one frame, monitor of most progressive scanning is scanned by image upside bottom, both effect is identical. Both effect is identical..
DVD is special design for interlaced scanning monitor. TV set of stage of whole world billion has 99.9% is interlaced scanning. However, the content of a lot of DVD comes from the film, be progressive scanning. Can work with interlaced scanning means to let film, the video that comes from every film frame is broken up every scanning field is; of field of two video scanning 240 lines; flows to code respectively with MPEG-2 data. Another problem is the film it is 24 frame / second, and if the television is NTSC is made for 30 frame (60 scanning field) per sec. , if be,SECAM is made, it is 25 frame (50 scanning field) per sec. . Show to PAL/SECAM, a simple settlement method is with 25 films frame / the second shows, indication rate rises 4% , frequency rate also rises accordingly. Show to NTSC, the means of settlement is it is 24 frame dispersedly in 60 scanning field, namely the field of 2 video scanning of frame of the first film mixes alternate displays the field of 3 video scanning of frame of the 2nd film. This is called 2-3 fold. Specific order shows as follows, a-D represents film frame;A1, a2, b1, the; 1-5 of field of two video scanning that waits to depart on behalf of each film frame represents final video frame.
Film frame: | A | B | C | D |
Video scanning field: | A1 A2 | B1 B2 | B1 C2 | C1 D2 | D1 D2 |
Video frame: | 1 | 2 | 3 | 4 | 5 |
To MPEG-2 encode, reduplicative scanning field (B1 and D2) do not store actually twice. Contrary, installed a mark to tell decoder to repeat field of this one scanning. (Because scan up and down,C2-C1 and D2-D1 out of order are an alternant place must. ) MPEG-2 also has mark to indicate a frame is progressive scanning (namely two scanning field results from same instant) . To film, this mark should be the progressive scanning frame of each frame True. Consult the detail of 3.4 more MPEG-2.
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