Field (video)
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In video, a field is one of the many still images displayed sequentially to create the impression of motion on the screen. Normally, two fields comprise one video frame, in what is known as 2:1 interlacing. 3:1, 4:1 and 5:1 interlacing also exist.[1][2] When the fields are displayed on a video monitor they are "interlaced" so that the content of one field will be used on all of the odd-numbered lines on the screen, and the other field will be displayed on the even lines. Converting fields to a still frame image requires a process called deinterlacing, in which the missing lines are duplicated or interpolated to recreate the information that would have been contained in the discarded field. Since each field contains only half of the information of a full frame, however, deinterlaced images do not have the resolution of a full frame. Sometimes in interlaced video a field is called a frame which can lead to confusion.[3]
To increase the resolution of video images, new schemes have been created that capture full-frame images for each frame. Video composed of such frames is called progressive scan video.
Video shot with a standard video camera format such as S-VHS or Mini-DV is often interlaced when created. In contrast, video shot with a film-based camera is almost always progressive. Free-to-air analog TV was mostly broadcast as interlaced material because the trade-off of spatial resolution for frame rate reduced flickering on cathode-ray tube (CRT) televisions. High-definition digital television (see: HDTV) today can be broadcast terrestrially or distributed through cable systems in either interlaced (1080i) or progressive scan formats (720p or 1080p). Most prosumer camcorders can record in progressive scan formats.
In video editing, knowing which of the two (odd or even) fields is "dominant." Selecting edit points on the wrong field can result in a "flash" at each edit point, and playing the video fields in reverse order creates a flickering image.
See also
[edit]- Federal Standard 1037C: defines the field in interlaced video.
- Color framing
References
[edit]- ^ Television Technology in Transition: Includes Selected Papers on Television Technology Presented During the 22nd Annual SMPTE Television Conference in Nashville, Tennessee, January 29-30, 1988. Society of Motion Picture and Television Engineers. 1988. ISBN 978-0-940690-14-1.
- ^ High Definition Television: Hi-Vision Technology. Springer. 6 December 2012. ISBN 978-1-4684-6536-5.
- ^ "InfoWorld". 11 June 1979.