[MPlayer-dev-eng] New inverse-telecine filter

Zoltan Hidvegi mplayer at hzoli.2y.net
Fri Dec 5 00:35:16 CET 2003

> > With interlaced downsampling the color samples will come from lines 0,
> > 1, 4, 5, 8, 9, ..., i.e., keep two lines, drop two lines.  If you do
> > that on a progressive frame, it will look bad, since every second
> > chroma line would be 1 luma pixel higher than normal, so you would
> > have to interpolate them back to the right place.  Probably you end up
> > losing 2/3 of the vertical chroma resolution instead of only losing
> > half if you did progressive downscale to begin with.
>   Ideally, it's not about keeping and dropping lines, you're supposed to
> apply a filter to get the chroma scanline, so the chroma scanline
> corresponding to scanline 5 should be filtered based on the neighbours
> in that field (1,3,7,9,...).  When you convert to 4:2:2 (or convert to
> progressive 4:2:0), you should also use a higher filter, and get a more
> accurate interpolation.I do not believe the argument that you will end
> up losing 2/3 of the vertical chroma resolution.

No matter how high filter you use, the samples you take will have a
wight center, and these centers will fall to two consecutive luma
lines, then they will skip two lines.  You have to re-align them for
progressive frames (which could be achieved by interlaced upscale
followed by progressive downscale), and I do not see how can you do
that without quality loss.

>   I also won't believe you if you say that doing the progressive
> downscale on progressive content will be _higher_ quality.  Keeping
> chroma from only one field seems like a bad, bad idea, given how NTSC
> encoding works.  I bet that if you did a proper upsample converting each
> field to 4:2:2, then merged them, then downscaled using a good filter
> back to 4:2:0, you would get a higher quality image.

That might be true if you used the nearest neighbor downscale the
first time.  bttv does that, so maybe you are right, although I'm
still not really convinced about that.  But really this whole
discussion we have is a bit moot, since we all agree on that for the
best quality you have to to do de-interlacing (de-telecine) on the
original 4:2:2 capture first, then we can use progressive downscale to
get progressive YV12 frames.


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