[noggin]

IVTC is a form of de-interlacing isn't it? (You are taking an interlaced signal and removing the interlace)

You are taking an interlaced signal, detecting the redundant field, and de-interlacing based on the position of this redundant field (i.e. weaving the pairs of non-redundant fields and then adding a 3:2 frame cadence again in most cases, so you can cope with mixed 3:2, 2:2 and native interlaced content in the same stream?)

It's not deinterlacing in the same sense as all the other algorithms, bob, weave, motion adaptive, etc.

It's pretty much identical to 2:2 without the discarded fields though isn't it? Which is just a Weave de-interlace (in many cases chosen when no intra-frame motion between field-pairs is detected) 2:2 Weave of 30p/25p in 60i/50i is also lossless.

3:2 IVTC (a term I hate - as you aren't reversing a telecine's operation - that would be putting video back onto film, and in many cases these days the 3:2 hasn't been introduced by a telecine) has to be part of a de-interlacing algorithm in most situations - as the 3:2 interlace cadence has to be detected (you can't rely on field-repeat flags in H264/MPEG2 streams) - so it is a decision taken by the de-interlacer whether to use 3:2 removal or not.

It perfectly recovers progressive frames at a different frame rate than the interlaced video by removing the telecine pattern. It doesn't discard spatial or temporal resolution or make decisions on what's interlacing and what's detail.

However when used real-time (as opposed to in file conversion) 3:2 IVTC, whilst it detects the duplicate fields and cleanly recreates the 24p sequence, it then usually re-inserts the 3:2 cadence in the progressive domain to ensure a constant frame rate sequence (otherwise your TV would be re-syncing on shot changes on shows like Letterman as they cut between 60i studio de-interlaced to 60p and a film clip containing 3:2 24p in 60i deinterlaced to 24p rather than 60p - though the 60p will be 3:2 without rogue mixed-field frames)

But the de-interlacer has totake the decision to use 3:2, and also has to take the decision when not to, which can mean some frames are temporarily incorrectly deinterlaced.