Interlace: A common way to compress video is to interlace it. Each frame of an interlaced video signal shows every other horizontal line of the image. As the frames are projected on the screen, the video signal alternates between showing even and odd lines. When this is done fast enough, i.e. around 60 frames per second, the video image looks smooth to the human eye.
Interlacing has been used for decades in analog television broadcasts that are based on the NTSC (U.S.) and PAL (Europe) formats. Because only half the image is sent with each frame, interlaced video uses roughly half the bandwidth than it would sending the entire picture.
Interlaced video frame consists of two sub-fields taken in sequence, each sequentially scanned at odd and even lines of the image sensor; analog television employed this technique because it allowed for less transmission bandwidth and further eliminated the perceived flicker that a similar frame rate would give using progressive scan. CRT based displays were able to display interlaced video correctly due to its complete analogue nature. All of the newer displays are inherently digital in that the display comprises discrete pixels. Consequently the two fields need to be combined into a single frame, which leads to various visual defects which the deinterlacing process should try to minimise.
Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form.
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