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Updated 14/11/2012Home » Video Glossary » Interlaced, non-progressive

Interlaced, non-progressive

Interlaced video is a technique of doubling the perceived frame rate introduced with the signal used with analog television without consuming extra bandwidth. Since the interlaced signal contains the two fields of a video frame captured at two different times, it enhances motion perception to the viewer and reduces flicker by taking advantage of the persistence of vision effect. This results in an effective doubling of time resolution (also called temporal resolution) as compared with non-interlaced footage (for frame rates equal to field rates). Interlaced signals require a display that is natively capable of showing the individual fields in a sequential order. Only CRT displays and ALiS plasma displays are capable of displaying interlaced signals, due to the electronic scanning and lack of apparent fixed-resolution.

Interlaced scan refers to one of two common methods for painting a video image on an electronic display screen (the other being progressive scan) by scanning or displaying each line or row of pixels. This technique uses two fields to create a frame. One field contains all the odd lines in the image, the other contains all the even lines of the image. A PAL-based television set display, for example, scans 50 fields every second (25 odd and 25 even). The two sets of 25 fields work together to create a full frame every 1/25 of a second (or 25 frames per second), but with interlacing create a new half frame every 1/50 of a second (or 50 frames per second).

To display interlaced video on progressive scan displays, deinterlacing is applied to the video signal (which adds input lag).