[opendtv] Re: HD vs. 625 vs. 525 vs. 405

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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