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

  • From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sun, 29 Aug 2004 18:06:50 +0100

Surely the Kell factor is NEVER applied in the design of a tv system? The
horizontal bandwidth defines horizontal resolution, and the raster defines
the vertical resolution. Kell never comes into the design, Kell calculates
the likely vertical resolution of the resulting system. In an ideal world,
these two values are identical or at least similar in terms of elements per
spatial unit, but I've never heard of any tv system being designed with Kell
in mind. Neither 525 nor 625 are square, nor is 1080i or psf or 720p on a
crt. Only 1920/1080p and 1280/720p are truly square on pixellated displays.

----- Original Message ----- 
From: "Terry Harvey" <tjharvey@xxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Sunday, August 29, 2004 4:04 PM
Subject: [opendtv] Re: HD vs. 625 vs. 525 vs. 405


> What I am saying is that the bandwidth allocated to the video channel will
> determine horizontal resolution. When 405 was designed, 3MHz was excessive
> in comparison with the later 525 and 625 systems. As a result, the 405
> picture element is narrow and not equally dimensioned vertically and
> horizontally.
>
> We would later acknowledge that the Kell Factor and interlace factor would
> be applied: but it wasn't applied when system A was designed.
>
>
> Terry Harvey
>
>
>
> At 03:49 PM 8/29/2004 +0100, you wrote:
> >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
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > >----------------------------------------------------------------------
> > > > > >You can UNSUBSCRIBE from the OpenDTV list in two ways:
> > > > > >
> > > > > >- Using the UNSUBSCRIBE command in your user configuration
settings
> >at
> > > > > >FreeLists.org
> > > > > >
> > > > > >- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the
> >word
> > > > > >unsubscribe in the subject line.
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> ----------------------------------------------------------------------
> > > > > You can UNSUBSCRIBE from the OpenDTV list in two ways:
> > > > >
> > > > > - Using the UNSUBSCRIBE command in your user configuration
settings at
> > > >FreeLists.org
> > > > >
> > > > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the
word
> > > >unsubscribe in the subject line.
> > > > >
> > > >
> > > >
> > > >
> > > >
> > >
>----------------------------------------------------------------------
> > > >You can UNSUBSCRIBE from the OpenDTV list in two ways:
> > > >
> > > >- Using the UNSUBSCRIBE command in your user configuration settings
at
> > > >FreeLists.org
> > > >
> > > >- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the
word
> > > >unsubscribe in the subject line.
> > >
> > >
> > >
> > >
> > > ----------------------------------------------------------------------
> > > You can UNSUBSCRIBE from the OpenDTV list in two ways:
> > >
> > > - Using the UNSUBSCRIBE command in your user configuration settings at
> >FreeLists.org
> > >
> > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
> >unsubscribe in the subject line.
> > >
> >
> >
> >
> >
> >----------------------------------------------------------------------
> >You can UNSUBSCRIBE from the OpenDTV list in two ways:
> >
> >- Using the UNSUBSCRIBE command in your user configuration settings at
> >FreeLists.org
> >
> >- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
> >unsubscribe in the subject line.
>
>
>
>
> ----------------------------------------------------------------------
> You can UNSUBSCRIBE from the OpenDTV list in two ways:
>
> - Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
>
> - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
>


 
 
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:

- Using the UNSUBSCRIBE command in your user configuration settings at 
FreeLists.org 

- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word 
unsubscribe in the subject line.

Other related posts: