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15.5. Cadence Detection (Motion Adaptive Deinterlacing Only)
The Deinterlacer II handles such video sequence by detecting the cadence and reconstructing (reverse pulldown) the original film. This is achieved by comparing each field with the preceding field of the same type (3:2 detection) or detecting possible comb artifacts that occur when weaving two consecutive fields (2:2 detection).
The 3:2 cadence detector tries to detect matches separated by four mismatches. When the 3:2 cadence detector sees this pattern a configurable number of times, it locks. The 3:2 cadence detector unlocks after configurable number of successive mismatches. Locking and unlocking thresholds for the 2:2 cadence detector are similarly configurable.
Refer to the Deinterlacing Control Registers section for more information.
If the incoming video contains any cadenced video, enable the Cadence detection and reverse pulldown option. Then, select the cadence detection algorithm according to the type of content you are expecting. If the incoming video contains both 3:2 and 2:2 cadences, select 3:2 & 2:2 detector.
The cadence detection algorithms are also designed to be robust to false-lock scenarios—for example, features on adjacent fields may trick other detection schemes into detecting a cadence where there is none.
The Deinterlacer II IP core also provides 3:2 & 2:2 detector with video over film option. Select this option to deinterlace correctly the subtitles, credits, or other closed-caption contents that were added over the top of movies or other cadenced contents. Because this feature introduces a field of latency to allow weave operations to be performed either forwards or backwards, also set the Fields buffered prior to output to 1.
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