[opendtv] Re: HD vs. 625 vs. 525 vs. 405
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 29 Aug 2004 15:49:28 +0100
I really don't know what you mean by this. The bandwidth of System A was
3MHz, Kell has nothing to do with that. It was an interlaced system with no
electrical vertical filters. The only vertical process done was in the
tubes, where the target was clear each field because the tube spot was big
enough (although plastic) to clear two lines worth of it in each sweep.
Again, Kell has nothing to do with this either.
The lenses were good because they came almost directly from the film
industry where 35mm standards had been applied. So the horizontal bandwidth
was nicely filled, as was the vertical bandwidth. Kell applies to the
vertical scan just as for all other scanned systems, as does the interlace
factor. So you get a lower perceived vertical resolution than you might from
the number of lines, just as for any other interlaced tv system.
Why do you say that Kell wasn't applied to it? Kell always applies to
scanned systems, that was his point. The interlace factor always applies to
interlaced systems as well. You can't get away from it, that's physics.
----- Original Message -----
From: "Terry Harvey" <tjharvey@xxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Sunday, August 29, 2004 3:13 PM
Subject: [opendtv] Re: HD vs. 625 vs. 525 vs. 405
> Maybe I applied the term Kell too loosely. And there are other facors
which
> made 405 pictures look sharp.
>
> Because the horizontal scan velocity was slower, it was more easilly
> handled by an early amplifier chain in terms of frequency response and
> phase response. Before the 405 closure, I made VHS recordings of the
> signal and when displayed it looks almost 'broadcast' quality. Also note
> the extended bandwidth given to the video channel as the Kell factor was
> never applied to 405 systems.
>
> Terry Harvey
>
>
>
> At 01:08 PM 8/29/2004 +0100, you wrote:
> >405-line pictures looked sharp but the late 50s simply because crt
displays
> >were being made with the spot too small for the raster. So you could see
the
> >lines. This became more and more true when we ran 405/625 dual standard
tv
> >sets, where the spot profile was a reasonable match to 625 and too small
for
> >625, so you could see black between the lines of 405. That made the
pictures
> >look artificially sharp. Kell never came into it.
> >
> >----- Original Message -----
> >From: "Terry Harvey" <tjharvey@xxxxxxx>
> >To: <opendtv@xxxxxxxxxxxxx>; <opendtv@xxxxxxxxxxxxx>
> >Sent: Sunday, August 29, 2004 1:42 AM
> >Subject: [opendtv] Re: HD vs. 625 vs. 525 vs. 405
> >
> >
> > > Okay I understand your definition and I was trying to say the same
thing
> > > from a different perspective. In system A, the E.M.I. engineers did
not
> > > account for the loss of the vertical resolution. And I am aware of
the
> > > Kell, Bedford and Trainer "Experimental Television Station"
Proceedings of
> > > the I.R.E. Volume 22 - 1934!
> > >
> > > In system M as you indicate, the Kell factor was applied to reduce the
> > > horizontal resolution by the factor of 0.7 to account for the apparent
> > > vertical resolution loss. In system A, the horizontal resolution is
higher
> > > relative to the vertical resolution because the apparent loss was not
> >taken
> > > account of.
> > >
> > > Maybe it would be more correct to say the Kell Factor was not applied
to
> > > system A. That is what I meant by saying the Kell Factor is unity. (I
> >will
> > > not bring interlace into this as it would further muddy the issue.)
> > >
> > > Perhaps then the sharpness of 405 received pictures can be accounted
for
> >by
> > > the excessive horizontal resolution applied.
> > >
> > > Terry Harvey
> > >
> > >
> > >
> > > At 12:09 PM 8/28/2004 -0400, Mark Schubin wrote:
> > > >Terry Harvey wrote:
> > > >
> > > > >The definition of Kell Factor is the number obtained by dividing
the
> >raster
> > > > >pitch distance by the width of the picture resolution elements.
> > > > >
> > > >No, it is not. The common definition of the Kell factor is the
> > > >reduction in vertical resolution from the number of scanning lines
> > > >(although, in the age of fixed-pixel displays, it has also been
applied
> > > >to the reduction in hirizontal resolution from the number of active
> > > >samples per line).
> > > >
> > > > >Recall that system A was developed in 1935/36, before Kell and
others
> > > > >discovered that the interlaced vertical resolution was not ideal.
> > > > >
> > > >Kell did his work in the early 1930s, before System A was broadcast.
> > > >
> > > >I have extensively researched Kell's work. I would suggest that you
> > > >look up the Proceedings of the IRE.
> > > >
> > > >TTFN,
> > > >Mark
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
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