[mythtv-users] Resolution

[audin at okb-1.org]

> > 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.

	Except that fields are layed down in succession.  All lines making up
the first field are layed down, then the lines for the second field.  So the
crosstalk (which is in fact deliberate in VHS EP/SLP recordings, the edges of
the scans actually overlap) is between alternate lines.  So you get both the
crappy quality of crosstalk AND the crappy quality of interlacing all at once.
:)

	VHS also has a general problem of only providing 3MHz bandwidth, while
a full NTSC signal is 6MHz...  I believe this is SVHS's major improvement, it
provides 5MHz or more.

-- 
                                            Audin Malmin - audin at okb-1.org

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