[opendtv] Re: Math of oversampling - a simple comparison
- From: Jeroen Stessen <jeroen.stessen@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 26 Apr 2005 09:02:55 +0200
Hello,
I wrote to Tom Barry:
>> But That Is Not The Way to properly down-sample a picture !
I wasn't aware of your reputation... When I mentioned your name
to my colleague, who uses Avisynth sometimes, he immediately
recognized it. You surely know what you are doing, especially
your motion compensated de-interlacer is appreciated.
Tom:
> Mostly agreed, I was working with what I had in hand. Though
> in practice DctFilter does not seem to do that badly.
In practice MPEG-2 does not seem to be doing that badly either,
and yet we sometimes see horrible quantisation artefacts. ;-)
Blocking artefacts are precisely caused by quantising away the
higher harmonics that are caused by cutting the picture into
blocks in the first place. Such an unnecessary artefact...
I think we agree that your picture was not very challenging
for the issue that we are discussing. If the higher DCT coefs
are almost zero anyway, then there is no harm in discarding
them. But that is too easy...
I should get a picture from the Euro1080 demo loop, and
perform some down- and up-scaling on it. Later.
Regards,
-- Jeroen
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