[MPlayer-users] -vf ilpack

[Ville Saari]

On Sun, Mar 07, 2004 at 10:39:19PM -0500, D Richard Felker III wrote:

> > True, but for such frames it wouldn't hurt if progressive chroma
> > subsampling is used too.
> 
> The way chroma sampling really works, you're right. However, if it
> worked the stupid way I used to think it did, bad things would
> happen...

Yes, but if each mpeg frame were unambigously tagged as either
progressive or interlaced, then each frame type could use optimal
chroma subsampling method. Too bad mpeg doesn't work that way.

> > I have also witnessed at least one case where 24 fps film content was
> > converted to PAL using 3:2:2:2:2:2:2:2:2:2:2:2-pulldown!
...
> Well normally this is done for movies where the music is the key
> feature, and increasing the pitch by 4% would butcher it.

It was an animated Mickey Mouse short film. Algorithms exist to
shorten audio without changing the pitch so that only the tempo of
the music would change. I actually believe that it is the usual way
to convert film to PAL nowadays.

If even that is unacceptable then there is still one option: The video
could be converted from 24 to 25 fps with motion compensated temporal
resampling. Hardware to do that is probably not cheap, but if I'm not
completely mislead, it at least exists. The video could even be
resampled form 24 to 50 fps to get true interlaced video from
progressive source.

> Linear blend doesn't kill vertical resolution. It does give slight
> blurring, but it's far from a dimension-halving filter like li,ci,fd.

Aren't the blurring and loss of resolution pretty much the same thing?
Most deinterlacing algorithms are effectively vertical low-pass filters.

> This still sounds bad... Care to write a nice filter to detect the
> ghosts from the previous frame and remove them? :)

Interesting problem. Adding some proportion of the difference of
current and previous frame to the current frame could do the trick
(kind of a sharpening convolution in temporal dimension).

Another similar problem is to fix progressive material that has been
NTSC-telecined and then deinterlaced. If the deinterlacing was done
by a method that uses just one field and invents the other, then the
fix is to simply drop the duplicate frame, but if the fields were
blended together, then the reconstruction of the frame that was split
between the interlaced frames is very similar to the ghost removal
problem.

-- 
 Ville