I'm processing a lot of telecined animation from DVD and find that any IVTC process, including TFM with access to the D2V file, sometimes produces blocky looking frames where it has combined top and bottom fields that consist of identical pixels, producing an output that's the same as if it had thrown away one field entirely, and scaled the remaining field to fill the image. the result is a blocky image that looks like the vertical resolution is halved. here's a screenshot showing the sort of thing I mean - lines 0 and 1 of the image are the same, lines 2 and 3 are the same, etc
and here's a better version of this frame produced by using an override file to choose a different match (I'm using mode 2 because on this dvd, every good match is always either c p or u)
the frequency of these bad frames varies depending on the show and the episode, but it happens to some extent with pretty much every episode of any DVD of telecined animation I have (I've got several well-known shows and they all exhibit this to some extent), at the moment I'm finding hundreds of bad frames in each episode around 40,000 frames long, but in some really bad cases there can be sections with a bad frame on every cycle of 5 frames. not only do these bad frames look awful and distracting when they appear, but they also mess up the decimation as they are almost always a blocky version of a neighbouring frame, so while they should be a candidate for decimation they instead look like unique frames. in the example above, the next frame is identical to the good frame I've shown, so that should be two identical frames that are candidates for decimation, but instead we have two unique frames
I've tried using overrides to fix this problem, and this is very successful - I can override almost every bad frame this way (on the two episodes I've done, I've removed hundreds and hundreds of bad frames leaving only 3-5 max), showing that good matches do exist but TFM is not choosing them. I've tried a myriad of modes and settings in TFM and while the results do vary, nothing stops these frames from being outputted in significant numbers. I think the problem is fundamentally that they are not combed frames, so there's nothing to identify them as a bad match, however to the eye they look terrible, and are very difficult to deal with using filters across the entire clip, without using extreme processing that does more harm than good to the rest of the clip. it's also difficult to identify and treat them separately in AVS, I've had some success with this but it feels like taking a hammer to fix hundreds of bad frames, when the better option is to output better frames in the first place. unfortunately using manual overrides to the extent required is an enormous process, it's taking around 10 hours to manually scan through and override all the bad frames in a single 23 minute episode, and I've got hundreds of episodes in each of multiple shows, which is why I'm here making this suggestion!
so - what would be really useful is if there was an "animation mode" for the field matching, where it would try to identify these frames and treat them the same way it does combed frames - rejecting them as matches, and passing through any leftover blocky frames that couldn't be avoided for post-processing (ideally I'd like to offer a clip3 for fixing blocky frames the same way I already use clip2 for combed frames, I have found that 2-3 stacked calls to QTGMC deals with the blockiness pretty effectively, but I obviously don't want to destroy the entire clip this way). I'm pretty sure these frames should be easy to detect - an algorithm similar to the one that detects combing by looking for significant pixel differences across several neighouring lines of pixels, could instead look for pixel differences that are aligned to odd/even pairs of lines only
I've never seen this issue with telecined live action stuff, it's only ever with animated material, which is why I suggested making it an optional "animation mode" but maybe it would work fine leaving this in place for all material, either way I think it would be a really useful feature for TIVTC resulting in better output for some difficult material
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