[opendtv] Re: Why Europe should choose 720P for HDTV

At 5:22 PM -0500 12/11/04, Tom Barry wrote:
>Yep, mocomp and other deinterlacers are not perfect and likely never
>will be.  For one thing they have to recognize when the vertical  motion
>is close to one of the multiples I just wrote about and realize that
>extra info is then useless.  And a million other things that are in the
>literature.
>
>But even if they just enhance otherwise good vertical scaling they are
>still definitely worth having.

Correct. This is black art, not science.

When there are gaps in the spectra of the source that you are 
de-interlacing, you have only a few choices.

Fudge it - just blur the entire image (at least all of the moving 
parts) to make the artefacts less apparent.

Paint it - try to predict what the missing information should look 
like then blend in the prediction with the surrounding pixels.

Predict it - actually predict the samples that are missing based on 
more advanced prediction techniques.

Sometimes prediction can work quite well. This is relatively easy 
when an object is moving in a consistent path and the surface of the 
object is "constant." This becomes quite difficult, if not 
impossible, when the objects are moving along inconsistent paths - 
like a football running back cutting through the line) with multiple 
players moving in different directions. And it gets worse.

What happens when the object is rotating and revealing surfaces that 
were not visible in previous frames?

What happens with reflections of objects that are non-linear? These 
are sometimes called plastic distortions or deformations, and they 
are impossible to predict without extensive 3D calculation, for which 
the most basic geometry is missing.

Another way of saying this, is to consider how to reverse engineer a 
single frame of a Pixar movie. If you have the algorithms and the 
basic geometry used to render the frame in the first place, you can 
do a good job. If you need to reverse engineer all of this in 1/60th 
of a second or even 1/24th...good luck.

That being said, the de-interlacers that are shipping in DTV monitors 
and receivers do a pretty decent job on SDTV source. I have little 
experience with HD source. I bought my first HDTV monitor 
specifically to watch NTSC - DEINTERLACED.

Delivering ALL source as progressive frames makes good sense for 
everyone. It helps MPEG-2 encoding.  It conserves channel bandwidth. 
It is easy to filter progressive source for interlaced display.

And yes Tom, vertical motion and interlace do not play well  together.

Regards
Craig

 
 
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