interlacing.png - Scanning Method A video frame is made of...

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Unformatted text preview: Scanning Method A video frame is made of horizontal lines that are scanned from one side of a display to the ether. Progressive video scanning happens when each line of a video frame is scanned, one after another. interlaced scanning fills the entire frame with only half the lines, which requires halfthe time,thus doubling the perceived frame rate and reducing flicker. About interlaced Scanning Frame rates lower than 40 fps can cause noticeable flicker. When NTSC and PAL were invented, faster frame rates were not practical to implement. Interlaced scanning was devised to create a perceived frame rate of fill fps [NTSCl or 50 fps [PAL]. Interlaced video scans the display twice, using two fields, to complete a single frame. A single field contains only the odd lines (1. 3, 5, I and so on} or the even lines {2,4, 6, B, and so on] of the frame. If you could stop the video scanning process to observe a single video field you would see that every other line is missing, like venetian blinds or a comb. Because the fields are changing at twice the frame rate,there is less perceived flicker than if each frame was scanned progressively. For example, with NTSC, a field of odd lines is scanned in lffifl ofa second and a field of even lines follows in the next use of a second resulting in a complete frame every use ofa second. ...
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