User guide

B–4 Appendix B: Choosing the Correct Deinterlacer
Cadence Detection and Reverse Pulldown in the Deinterlacer II MegaCore Function—In Depth
Video and Image Processing Suite January 2013 Altera Corporation
User Guide
For broadcast, a telecine is applied to minimize artifacts due to the rate conversion,
which introduces a 3:2 cadence to the fields, as shown in Figure B–5:
A video sequence such as Figure B–5 may be correctly handled by detecting the
cadence and reconstructing (reverse pulldown) the original film. You can achieve this
by comparing each field with the preceding field of the same type (3:2 detection) or
detecting possible comb artifacts that occurs if weaving two consecutive fields (2:2
detection), as shown in Figure B–6:
The 3:2 cadence detector tries to detect matches separated by four mismatches. When
this pattern is seen a couple of times, the 3:2 cadence detector locks. The 3:2 cadence
detector unlocks after 11 successive mismatches.
After six fields of cadenced video is presented, the 2:2 cadence detector will lock.
After three fields of uncadenced data is presented, the 2:2 cadence detector will
unlock.
Figure B–5. Incoming Interlaced Video
Figure B–6. 3:2 Detection and 2:2 Detection Comparison
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