» Judder and Anti-judder

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Movies for the cinema shot on 35mm or 70mm film capture 24 individual images (frames) per second which are projected at 48 frames per second to reduce flicker. To achieve 48 frames per second each frame is projected twice.

Television broadcast systems are field based. For example, NTSC (National Television Standards Committee) Video is interlaced with each frame being constructed from two consecutive fields of video containing 50% of the 480 horizontal scan lines containing picture information. NTSC video displays at 29.97 frames or 59.94 fields per second.

Overcoming the frame rate mismatch (24 versus 29.97) to allow movies captured on film to be viewed with video equipment (eg. HDTV) is called Telecine.

To bridge the frame rate gap a frame repeating system called 3:2 pull-down is used turning every other frame of the film into three fields of video. It works well apart from the fact that two out of every five video fields come from different frames and when there has been image movement between frames (eg. camera is panning) there is a mismatch (smearing) of detail between the sequential fields making a frame. The human eyes persistence of vision takes care of smoothing this anomaly apart from some situations like slow panning or spinning objects. Frame mismatch makes films look subtlety less smooth on home video equipment as opposed to the cinema screen and is termed telecine judder. Other television broadcast systems such as PAL suffer the same judder problems as NTSC.

Anti-judder video processing techniques are all aimed to smooth the judder produced by the process of making 24 frame rate films viewable on video equipment (telecine). There is no perfect solution as they all work on interpolating missing information.

Anti-judder video processing technologies are aimed to alleviate this annoying visual effect. An example is Hitachi’s Reel60.