[opendtv] Re: Digital vs. Analog Quality

  • From: Cliff Benham <flyback1@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 07 Jul 2008 13:17:13 -0400

Cliff Benham wrote:
Craig Birkmaier wrote:
It is true that the luminance bandwidth can exceed the
4.2 MHz bandpass of an NTSC encoder, but the process of creating the I & Q components for baseband video is the same process used in an NTSC encoder - you must reduce the Q component (mostly blue) to only 0.5 MHz bandpass and the I component to 1.5 MHz.

While the FCC rules for broadcasting analog NTSC specify I&Q as the color components, I think for most digital OTA broadcasts wideband R-Y&B-Y are used which, when decoded into NTSC in the $60 boxes results in images with much more color detail.


Sorry, I left out the background for this statement...

DVDs, S-Video, and DTV broadcasts have 120 lines of chroma resolution,
as opposed to NTSC broadcast over the air with 40 lines of chroma resolution.
This is a good link about such matters:
http://members.aol.com/ajaynejr/vidcolor.htm
And this one delves even deeper into color resolution:
http://members.aol.com/ajaynejr/vidcol2.htm

There is also a very useful signal in a Tektronix 130 Test Generator:
The Chroma Bandwidth Test Signal. It is a chroma sweep signal with
markers every 250 Khz from 2.58 to 4.58 MHz; to wit-
2.58, 2.83, 3.08, 3.33, 3.58, 3.83, 4.08, 4.33, and 4.58 MHz.

My Philips Standard def HD-DVD recorder/receiver records and plays this signal quite well. See pic.

JPEG image

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