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interpolating interlaced video to mimic 25p


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#1 David Bradley

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Posted 05 March 2007 - 08:59 PM

I'm getting really tired of shorts shot on interlaced video. Unfortunately par the 'cineframe' (faux progressive) function on my Z1E I only have access to a dsr570wsp (pal).

I want to de-interlace the video in post from 50i to 25p. What program if any would allow me to do this (preferably Avid xpress pro hd if anyone knows how to configure it to do so).

Also would it create a 'film look' without any nasty blemishes or artefacts?

Could someone explain interpolation to me?
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#2 Phil Rhodes

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Posted 05 March 2007 - 10:24 PM

Hi,

Usually there are a few options for how you do this. Most basically, you can duplicate the first field into the second (or vice versa, if you have some very specific reason for wanting the odd lines rather than the even). This gives you true progressive frames with half the vertical resolution and half the effective shutter angle. Slightly more subtly than that, you can have the computer interpolate the missing lines from those it does have - effectively, estimate what information would be there by averaging what is around it. This doesn't intrinsically offer you any more resolution than the first effort, but it's generally easier on the eye as it's soft rather than jaggy. This is more or less what Cineframe does on a Z1, but the interpolation is as basic as you'd expect from the embedded electronics in a consumer grade camera - you can do much better in software on a computer. Compare this with the results from "nearest neighbour" resampling in Photoshop as opposed to a proper bicubic interpolation. The canon cameras are better at this but still no patch on a proper software interpolation.

If I were you, given that these techniques cost you resolution, I'd unhesitatingly shoot with the Z1 and deinterlace it in post. I don't really know Avid that well, but you could also do it in Virtualdub, which is free, if you can get it into an AVI file format of some kind. There are smart deinterlacers, also free, for virtualdub, which look for interlace artifacts in the image and apply interpolation only to those areas, but I've had mixed results - set the thresholds too high and you get intermittent blurring on areas of the picture that happen to contain horizontal detail that looks like interlacing, set it too low and you get horrible jagged bits of interlace coming through. Minefield, but it can give you superior results if you are willing to play with it because it only blurs things which are moving, and thereby probably motion blurred anyway.

Phil
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#3 Gary Mc Nally

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Posted 22 March 2007 - 05:09 AM

I've had success using Adobe After effects to deinterlace footage.

Theres a great video guide on how to do it

http://forums.creati...lace/index.html

I did some of my uni work last year using this process and it worked a treat.

Hope that helps.
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