Re: Issue with deflicker, deinterlacing of film capture in Virtualdub
- From: "Jukka Aho" <jukka.aho@xxxxxx>
- Date: Mon, 28 Aug 2006 15:33:47 +0300
Doc wrote:
I find that applying a deflicker filter - in this case the MSU
deflicker - to a file of captured film causes an undesirable
flickery "contrail" effect in the image similar to the "tail"
setting you can elect for the mouse cursor in Windows (though
why anyone would want their cursor to look like that escapes me).
The mouse pointer trails option is intended for slow TFT displays - such as those used on old laptops - where the pointer easily goes "missing" when you move it (because of the slow response time and inherent motion blur of the display.)
Through experimentation, I find that checking the deinterlace
option in the white balance filter and further NOT choosing
"interlaced" in the resize filter, this artifact goes away.
[...] Why is this? Is there a better way to eliminate it?
It sounds a bit like the MSU filter just wasn't made for interlaced material. It probably gets distracted as the overall brightness of the images varies not only from frame to frame, but also from field to field.
One way to eliminate it would be shooting the material again with a better DV camcorder that can be set into progressive scan mode. (However, this usually isn't practical if you don't already own a camcorder with such a capability.)
Another way - which is probably worth trying out here - would be
1) separating the fields from each other and processing them as if they were a sequence of frames (the fps being the original field rate)
2) applying the MSU deflicker filter and
3) weaving the processed fields back into interlaced frames.
As far as I know, there is no easy way of doing all this field separation / recombining stuff in VirtualDub alone. You can do it in AviSynth, though. (If you know what you're doing, it is even possible to use VirtualDub filters in AviSynth, so you could do _all_ processing there, without saving into intermediate files.)
I was under the impression that the reason for interlacing is
because a TV scans 2 different fields to yield a complete image.
Yes, that's part of the story, but that's not all there's to it. Adjacent even/odd field pairs represent not only spatially different data, but also temporally different data. In other words, each field is shot at a different moment in time.
The following web sites should help in grasping the idea better:
<http://www.lurkertech.com/lg/fields/fields.html>
<http://en.wikipedia.org/wiki/Interlace>
<http://www.100fps.com/>
Does deinterlacing reduce the image quality?
"Deinterlacing" involves generating data out of thin air - information that wasn't there in the first place. There are various algorithms for doing it - ranging from very simple and crude to complex ones - but it is often done in a crude manner that involves loss of vertical resolution, at least in the moving parts of the image, and cuts the motion quality and fluidity into only a half of the original.
Whether there is a real need for deinterlacing depends on your target format and audience. If the video is going to end up viewed on a normal tv set in a regular, standard video format (for example, by using a DVD player, VCR or a DV camcorder), deinterlacing is a pointless act and will only make the image and motion quality worse. On the other hand, if the target format is, say, a postage-stamp sized video stream embedded on a web page, deinterlacing (and, usually, resampling to a smaller size) may be required.
Whenever possible, it's usually better to keep interlaced material in its original format - interlaced - and let the video player deal with deinterlacing in environments where necessary. (For example, software-based DVD players can usually deinterlace on the fly.)
--
znark
.
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