Quantcast Half chroma info on deinterlacing VHS? - digitalFAQ Forum
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07-24-2018, 12:02 PM
Feedbucket Feedbucket is offline
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Hi - working with a commercial VHS source.

When I deinterlace into 2x frames and view the resulting chroma using UToV() it appears that the same info is used for both the top and bottom fields. I'm guessing the source uses 420 subsampling and that this is what happens when the source is interlaced -- I've read that the chroma info should be retained for the second field in the sequence, but it seems logical to me that it might get dropped altogether since the source frame should contain only half the info at most. The DVD of the same scene behaves in the same way.

In any event, the net effect is that every other rendered frame uses the chroma from the frame that immediately precedes it rather than its own, resulting in strange discoloration during sequences where motion takes place. Assuming I do want to double the frames -- most of the info is there, so why not use it, and my intention is to view this in a PC-driven environment, not a TV (so no hardware deinterlacing) -- I'm interested in knowing where I should go from here. Is there something wrong with the source? Am I doing something wrong? I imagine one way to fix this is to interpolate the chroma temporally -- is there a good way to do this?

Thanks.
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07-24-2018, 09:44 PM
sanlyn sanlyn is offline
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Your video isn't interlaced or might be telecined, or is progressive video encoded with soft-coded interlace flags.

Quote:
a PC-driven environment, not a TV (so no hardware deinterlacing)
You've been duped by people who don't know what they're talking about. Today's TVs are just as progressive as your PC media players. If your PC media player can't deinterlace, it can't inverse telecine either -- which means it's a pretty stupid player. Use something else.
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07-24-2018, 10:50 PM
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Quote:
Originally Posted by sanlyn View Post
it can't inverse telecine either -- which means it's a pretty stupid player.
Do HDTVs, Blu-ray players, etc, do IVTC? I didn't think so. But I've honestly never given it much thought. I worry mostly about the deinterlacers. And I'm under the impression that the deinterlacers still process the telecined material. But I could be wrong here. Interesting.

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07-25-2018, 05:37 AM
sanlyn sanlyn is offline
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Quote:
Originally Posted by lordsmurf View Post
Do HDTVs, Blu-ray players, etc, do IVTC?
Yes. Some do it better than others.
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07-25-2018, 12:49 PM
Judd_the_budd Judd_the_budd is offline
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I guess I better keep reading, because I have no idea what any of you are talking about.
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07-25-2018, 01:20 PM
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Originally Posted by Judd_the_budd View Post
I guess I better keep reading, because I have no idea what any of you are talking about.
It's mostly non-VHS stuff, so probably more trivia for you than not.

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