[opendtv] Re: Why Europe should choose 720P for HDTV
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 13 Dec 2004 10:07:35 -0500
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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