[opendtv] Re: HD vs. 625 vs. 525 vs. 405
- From: Terry Harvey <tjharvey@xxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 29 Aug 2004 07:13:26 -0700
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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>
>
>
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