Editing Interlaced video (section)

==Description==
{{Unreferenced section|date=May 2023}}
[[File:Balayage entrelace affichage trames.svg|alt=Interlaced scanning: display of the odd and even frames, and line returns|thumb|250px|Interlaced scanning: display of odd (green) and even (red) scanlines, and line return blanking periods (dotted)]]
[[Progressive scan]] captures, transmits, and displays an image in a path similar to text on a page—line by line, top to bottom.
The interlaced scan pattern in a standard definition CRT display also completes such a scan, but in two passes (two fields). The first pass displays the first and all odd numbered lines, from the top left corner to the bottom right corner. The second pass displays the second and all even numbered lines, filling in the gaps in the first scan.

This scan of alternate lines is called ''interlacing''. A ''field'' is an image that contains only half of the lines needed to make a complete picture. In the days of CRT displays, the afterglow of the display's phosphor aided this effect.

Interlacing provides full vertical detail with the same bandwidth that would be required for a full progressive scan, but with twice the perceived [[frame rate]] and [[refresh rate]]. To prevent flicker, all analog [[broadcast television systems]] used interlacing.

Format identifiers like 576i50 and 720p50 specify the frame rate for progressive scan formats, but for interlaced formats they typically specify the field rate (which is twice the frame rate). This can lead to confusion, because industry-standard [[SMPTE timecode]] formats always deal with frame rate, not field rate. To avoid confusion, SMPTE and EBU always use frame rate to specify interlaced formats, e.g., 480i60 is 480i/30, 576i50 is 576i/25, and 1080i50 is 1080i/25. This convention assumes that one complete frame in an interlaced signal consists of two fields in sequence.