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line doubling

See deinterlace.


To convert an interlaced image to a progressive scan image. Also called "I to P conversion," deinterlacing is built into most DVD players, A/V receivers, video processors and digital TVs. Most broadcast TV is delivered in 1080i resolution (1080 lines "I"nterlaced) and many DVDs include interlaced content. Deinterlacing fills in the missing lines so that 60 full frames per second can be displayed on HDTV sets. See interlace.

EASIER: Film to Interlaced to Progressive
When a movie shot on film is converted to video, all original content is available in the video frames. Each full movie frame is turned into two interlaced video half frames (see telecine for details), and the half frames can be readily converted back into full frames, restoring the original, progressive sequence. The cadence detection in the deinterlacing process analyzes the frame sequence to determine if the video was originally film in order to deinterlace the frames in this manner (see cadence correction).

MORE DIFFICULT: Interlaced to Progressive
When shooting with a video camera, interlaced video is generated from the start, in which even lines are captured for one half frame followed by the odd lines in the next half frame and so on. Since the camera keeps running and generating half frames, every other line is actually missing in the video frames. In order to deinterlace this originally interlaced video, either the existing even and odd lines are duplicated, called "line doubling," or the missing lines are filled in by analyzing the half frames before and after each half frame. This is where one algorithm can be vastly superior to another. See interlace, DCDi and telecine.

Eliminate the Jaggies
Anchor Bay's VP50Pro video processor cleaned up the original video frame (upper left) by analyzing the scene and applying different algorithms to the static and moving parts of the image. (Image courtesy of Anchor Bay Technologies, Inc.,

From 480i to 720p
To convert a 480i signal to 720p or 1080p, the first step is to deinterlace the 480 lines from 480i to 480p and then upconvert to the higher resolution.

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