[mythtv-users] Resolution

James L. Paul james at mauibay.net
Wed Dec 3 17:27:35 EST 2003


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On Wednesday 03 December 2003 12:02, DBakker at arrayasolutions.com wrote:
> Great info in this thread.
>
> Does anyone know what a DirecTV receiver output resolution is (SVideo)?

My understanding is that S-Video signal quality is effectively equivalent to 
SVHS and 352x480.

For a really good article on 352x480, CVD resolution and 1/2 D1 and it's 
relationship to S-Video/SVHS, read here:

http://www.dvdrhelp.com/forum/userguides/98177.php

> -David
>
>
>
>
> "Boyd II, Willy" <wboyd at fulbright.com>
> Sent by: mythtv-users-bounces at mythtv.org
> 12/03/2003 04:19 PM
> Please respond to
> Discussion about mythtv <mythtv-users at mythtv.org>
>
>
> To
> "'Discussion about mythtv'" <mythtv-users at mythtv.org>
> cc
>
> Subject
> RE: [mythtv-users] Resolution
>
> >-----Original Message-----
>
> From: James L. Paul [mailto:james at mauibay.net]
>
> >Sent: Wednesday, December 03, 2003 3:08 PM
> >To: papenfuss at vt.edu; Discussion about mythtv;
> >papenfuss at juneau.me.vt.edu
> >Subject: Re: [mythtv-users] Resolution
> >
> >
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> >On Wednesday 03 December 2003 10:30, papenfuss at juneau.me.vt.edu wrote:
> >> On Wed, 3 Dec 2003,  James L. Paul wrote:
> >> > > SO, with this in mind, take a few data points.  NTSC VHS has 240
> >> > > lines. Formatted at 4:3, this translates into 480
> >
> >vertical pixels
> >
> >> > > (NTSC viewable scan lines), and horizonally (240 * 4/3) = 320.
> >> > > So, to capture VHS-quality video, you need a capture
> >
> >resolution of
> >
> >> > > 320x480... 1/2 D1 is close at 352x480.  To capture high-quality
> >> > > broadcast at 330 lines, (330 * 4/3) = 440... SVCD is close at
> >> > > 480x480.  Capturing any more than that wastes encoding time,
> >> > > space, encoding quality, etc.
> >> >
> >> > This is a much better description than mine. As I remember
> >
> >it though
> >
> >> > there was some effect caused by interlacing, real-world signal
> >> > loss/distortion and quality of video tape that made VHS generally
> >> > considered 352x240, although I can see now the 352 is obviously
> >> > inflated. (Perhaps that explains why all the VCDs I made from my
> >> > DirecTV looked better than VHS from the same source.) I think it's
> >> > the way the interlaced frames are helically laid down on the tape,
> >> > there is significant bleed on VHS, but SVHS used denser tape and
> >> > probably smaller heads.
> >>
> >>               The 352 is not all that inflated.  At the rated 240
>
> lines, that
>
> >> equates to 320 pixels horizonally.
> >>
> >> > So the way I understood it, although all NTSC video has 525 lines,
> >> > about 480 of them viewable, the analog storage and reproduction of
> >> > VHS tape doesn't accurately retain the resolution of all them, and
> >> > results in about half. It's as if the interlaced video
> >
> >interpolates
> >
> >> > itself unnecessarily. This may be totally wrong. I've never
> >> > questioned it though since seems to match my experience.
> >>
> >>               I thought about that, and that's actually what I was
> >
> >thinkign when I
> >
> >> was searching for the definition of resolution.  I'd be tempted to
> >> believe it, but remember that two adjacent lines on the
> >
> >screen are put
> >
> >> on the tape 1/30th of a second later (well, 1/29.97th, but who's
> >> counting!).  If they were to bleed into each other, they
> >
> >would soften
> >
> >> the whole thing up so that you couldn't distinguish
> >
> >individual fields.
> >
> >> Recording from VHS tape at 480 vertical pixels definately shows a
> >> clearly interlaced picture.
> >>
> >>               I'm not saying that there's not bleed-through between
> >
> >adjacent scans
> >
> >> on the tape, but it's not much of a factor.
> >
> >I wasn't talking about bleed that way, perhaps bleed is a bad
> >word choice. Of
> >course you get properly interlaced video. I meant that the
> >nature of storing
> >analog signals on magnetic tape so closely together and the process of
> >writing/reading them with a head that isn't fine enough to
> >completely avoid
> >the adjacent signal of the interlaced fields on the tape.
> >
> >The signal on the tape has a strong center and drops off
> >sharply the farther
> >you get from the center, and the interlaced field signals are written
> >alternately adjacent to each other. It was the signals being
> >so close to each
> >other on the tape that I meant by bleed. As each field is laid
> >down on the
> >tape, the recording head isn't far enough away from the
> >previous field to
> >totally avoid affecting it, and the same thing happens when
> >reading, the read
> >head gets the center of the field but isn't totally unaffected
> >by the two
> >interlaced fields next to it. This is all part of what gives
> >VHS the quality
> >it has. (Or doesn't have, as the case may be.)
> >
> >Disclaimer: I don't have any references to back this up, I
> >don't remember
> >where I learned this, and I may be full of hot air on this one.
> >
> >As for beelding into each other such that they soften up or
> >being unable to
> >distinguish individual fields, this does happen, and it's why
> >VHS has a shelf
> >life. I have tapes from 20 years ago that are unplayable now,
> >and others that
> >get worse each year when I pop them in to check. (I do this
> >out of curiosity,
> >I started archiving my VHS to VCD in 1996, and switched to CVD
> >in 2001, and
> >now use DVD. Every year of so I sit down and play tapes I
> >"rescued" to see
> >how long they actually lasted. :)
>
> Just out of curiousity, do you use a certain brand of cd-r or dvd-r discs
> in order to maximize shelf life for those archives?  (I'm merely
> piggy-backing off your archival
> research :-)
>
> - Willy
>
> >> -Cory
> >>
> >>  --
> >
> >***************************************************************
> >**********
> >
> >> * The prime directive of Linux:
> >
> >                *
> >
> >> *             - learn what you don't know,
> >
> >                *
> >
> >> *             - teach what you do.
> >
> >                *
> >
> >> *             (Just my 20
> >
> >USm$)           *
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