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Old September 10th, 2011, 10:22 AM   #1
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motion blur problem - advice needed.

Hi,

I've posted about this before, a while ago so sorry for the repetition but have yet to find a solution so thought it worth asking agin for the wisdom of the board.

Below is a clip which shows unpleasant motion blur on the figure moving across the screen which plagues this whole film (ignore the slight jitter at the end). I'm certain this is an interlacing issue as when viewed from the original HDV tape, via my hardware set-up (FCP and Matrox mini to an HDTV) or on DVD via a dedicated DVD player, the motion is smooth and perfectly normal looking - all these playback mediums are designed to cope with interlaced material or are natively interlaced mediums.

But when viewed as a file (any type that I've tried) on computer it always looks like this no matter what I do - this version is H.264 and *is* de-interlaced; I have tried all sorts of de-interlacing methods from quick and blunt to highly sophisticated but none of them make any difference at all so I've come to the ultimate conclusion that this film will never look right when viewed on-line or as QT file or similar.

Am I right? - does anyone have any possible solutions?

Thanks.

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Old September 10th, 2011, 11:26 AM   #2
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Re: motion blur problem - advice needed.

I'm not an expert on this so am just guessing...

Aren't there different deinterlacing methods, like Bob and Blend and Lanczos and such? Clearly the interlacing lines are gone but it's clear there are still two overlapping fields. It appears they have taken two fields and tried to blend them into a single frame by overlapping them and interpolating the lines. Maybe a different method will yield a different look, more akin to a simulated 50p.

I've also been told there is an inherent mismatch if you shot 50i and are displaying on a 60Hz monitor, as most are.

It's also possible you have a field reversal issue. I've deinterlaced plenty of 60i material and have never come across anything looking like this. But if it's fine on DVD then that's probably not it.

Upon reflection, I'm probably completely wrong.....
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Old September 10th, 2011, 12:05 PM   #3
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Re: motion blur problem - advice needed.

Thanks Adam - yes your idea does make sense to me since as you say, the two overlapping fields are still there and that seems to be what is making it look so awful but how to solve it is the issue - maybe a special d-i method will do it, but which one - I've tried all the various types in VLC player which do it on the fly and there is no difference at all!

As for field order, the images are HDV top field first and have remained that way at all stages so I can't see where they would have been reversed.

I know about 50i and 60Hz monitors but don't think that is what is causing this...
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Old September 10th, 2011, 01:50 PM   #4
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Re: motion blur problem - advice needed.

I see your vimeo clip is 1280x720 - is your original HDV clip 720p as well? Probably you're shooting 1440x1080i, as there are few camcorders that shoot HDV 720p natively, (and if your original clips were 720p, you wouldn't have to deinterlace...)

The reason I mention it is this - it's important to deinterlace before resizing. After a good deinterlace, resize using a Lanczos method if possible. Have you tried Handbrake? A great freeware h.264 encoder that has good resizing.
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Old September 10th, 2011, 02:21 PM   #5
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Re: motion blur problem - advice needed.

Looks like you are using frame blending.
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Old September 10th, 2011, 02:50 PM   #6
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Re: motion blur problem - advice needed.

Seth,

The original is 1440x1080 50i so I tried using handbrake for both de-interlacing and resizing (did them simultaneously) as you suggested and as you can see below it is much better! I think in fact it is Hanbrake's deinterlacer that is crucial here as one can no longer see both fields. Many thanks:

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Old September 11th, 2011, 02:39 AM   #7
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Re: motion blur problem - advice needed.

HDV seems to show this a lot more and I had similar problems when using my Z7 and S270, the 25p mode is not brilliant on those camera's either so I tended to do as you and shoot 1440x1080i 50i and then de-interlace and do 720p in software.

I use P2 now and don;t seem to have the same problems but there again I am shooting on a far superior codec AVC Intra and at true 25np.
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Old September 11th, 2011, 07:06 AM   #8
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Re: motion blur problem - advice needed.

Interestingly I found that if I convert the file to 50 progressive frames per second (from 50i) it looks absolutely fine when played back in QT which is good news (my ignorance means I'm not sure why this should be other than that each half frame becomes a full frame?). But I can't show you this as Vimeo does not support 50fps - it plays it but presumably just at 25fps though not sure what it decides to play - every other frame? I don't know a way round this.

So I have a solution for QT playback but not for web streaming, though the earlier de-interlacing / resizing suggestions have improved things a bit so thanks to all.

And thanks Gary - it does seem that this might be an inherent HDV codec issue.

EDIT: Actually I tell a lie if you go here (go to the vimeo page itself) and select download video in the bottom RH side you can see the 50fps version:


Last edited by Geoffrey Cox; September 11th, 2011 at 07:12 AM. Reason: new info
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Old September 11th, 2011, 09:25 PM   #9
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Re: motion blur problem - advice needed.

I made this mistake enough times to tell you for sure, it's field reversal. Somewhere along the processing you inverted the field order.
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Old September 12th, 2011, 03:44 AM   #10
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Re: motion blur problem - advice needed.

Ervin, I recorded to tape, I transfrerred to FCP, I exported to QT - where could have a revresed the field order?

I also used software to reverse the order on this file just to check this anyway and it made no difference.

But... do tell me the way to test this definitively and rectify it if indeed somehow the fields are reversed.

Thanks
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