[MPlayer-dev-eng] [PATCH] -vf combdetect: crude detection of interlaced sources

[Reimar Döffinger]

On Mon, Aug 02, 2010 at 03:50:30PM +0100, Christopher Key wrote:
> As mentioned, this is very crude.  It works well for my library of PAL
> dvds, which will either be 24fps film sped to to 25fps, or natively
> 50f(ields)ps interlaced TV, but isn't designed to analyse NTSC material
> that may use 3:2 pulldown etc.  This is why I've named it combdetect,
> that's all it does, and it leaves room for a more advanced filter than
> can detect a rather broader range of field/frame fiddling techniques. 
> Nevertheless, I find this very useful, and suspect that it may be useful
> to others with similar aims.

But even for detecting combing it should be quite simple to do a lot
better, e.g. by comparing C(line i, line i+1) to C(line i, line i+2) where
C is the covariance.
But even without going that far, the property of combing is not that
line i differs a lot from line i+1 but that line i+1 differs _more_ from
line i than line i+2.
Thus your filter only detects a high variance vertically but has not
much to do with combing IMO.