Video and Image Processing Suite User Guide

ID 683416
Date 2/12/2021

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15.5. Cadence Detection (Motion Adaptive Deinterlacing Only)

Motion-adaptive configurations of the Deinterlacer II IP core provide the option to detect both 3:2 and 2:2 cadences in the input video sequence, and perform a reverse telecine operation for perfect restoration of the original progressive video.
The video over film feature allows non-cadenced sections of video to be deinterlaced normally, regardless of the cadence. The video over film feature also enables enhanced scene change detection and a comprehensive register map for debugging and tuning the deinterlacer performance.
Note: Intel recommends you enable this feature for broadcast quality deinterlacing applications.
Figure 58. 2:2 Cadence (Progressive Segmented) ContentThe figure below shows an example of four frames from a film; each frame is split into odd and even fields.
Figure 59. 3:2 Cadence

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).

Figure 60. 3:2 Detection and 2:2 Detection ComparisonThe figure below shows the comparison between 3:2 and 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.

Figure 61. Weave Current and Weave PastWhen the cadence detect component enters a lock state, the deinterlacer continuously assembles a coherent frame from the incoming fields, by either weaving the current incoming field with the previous one (weave current) or by weaving the two past fields together (weave past).

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.