[opendtv] Re: Video compression artifacts and MPEG noise reduction

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 14 Jun 2008 10:27:00 -0400

At 5:45 PM -0400 6/13/08, Manfredi, Albert E wrote:
It's useful also for broadcasters who want to transmit more multicasts,
or to reduce the artifacts in the multicasts they transmit now. I know
WETA-DT, with its 4 multicasts, including one HD, could make use of such
a product.

I do not understand how this could be of use.

This is a post processing technique to help mitigate the damage done by the use of excessive levels of compression. In virtually ALL cases, the quality of the feeds that go into a stations multiplex are not the problem; the feeds are typically uncompressed (either physical media or satellite feeds), or lightly compressed contribution feeds.

The problem is that the station must apply considerable compression to these feeds in order to make them fit into the multiplex. The only way to undo this damage would be to build the kind of processing that the Algolith product is offering into the receiving/display device - preprocessing at the station is irrelevant.

It would be fun to see a comparison of this against H.264. In essence,
what this Algolith product does is a clever pre-filtering, before MPEG-2
encoding, as opposed to the more meat axe approach to prefiltering you
might see now. Makes sense. Since the H.262 encoder is well understood,
it should be possible to use digital filtering techniques before it, to
prevent the H.262 encoder from becoming overwhelmed. With a digital
pre-filter that knows what specific aspects of the given video will
overwhelm H.262, image pre-filtering should be possible with reduced
image degradation.

NO. That IS NOT what the Algolith product is doing. It is a POST PROCESSING device that attempts to undo the effects of pre-processing (e.g. lop pass filtering) and the artifacts of MPEG-2 compression.

Most commercial MPEG-2 encoders DO include noise reduction and pre-filtering that operates in closed loop with the encoder. If the encoder is stressed, the low pass filter is used to reduce encoder stress.

 It's hard to imagine consumers putting such a processor on
 their TVs.

But it's not so hard to believe that the manufacturers of especially
large TVs would build this, or similar, into their products.

They already are.



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