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

The now discontinued system A (405 lines interlaced 50Hz) baseband 
broadcast video channel was 3MHz wide. This compares with system M (525 
lines interlaced 60Hz) which is 4.1 MHz. This means that, relative to the 
horizontal scan rate and number of raster lines, the horizontal resolution 
ratio to vertical resolution of 405 lines is greater.

The definition of Kell Factor is the number obtained by dividing the raster 
pitch distance by the width of the picture resolution elements. According 
to the Blair/ Whitaker "Television Engineering Handbook" (1992) pages 4.8 
and 4.9, you will see that with system M, the picture element width is 21 
units and length 30 units: the ratio is 0.7. With system A, The picture 
element width is 27 and the length is 28 for a ratio of 0.96, which I would 
round off to one.

Recall that system A was developed in 1935/36, before Kell and others 
discovered that   the interlaced vertical resolution was not ideal. Hence 
when in the U.S.A. 441 lines with double sideband transmission (later 
superceding by 525 vestigial sideband) was introduced, the Kell compromise 
was reached.

Terry Harvey


At 10:34 PM 8/27/2004 -0400, Mark Schubin wrote:
>Terry Harvey wrote:
>
> >Also, the Kell factor was 1.0 instead of 0.6
> >for 525 systems.
> >
>I do not believe there was ever a CRT display with a Kell factor of 1.
>
>TTFN,
>Mark
>
>
>
>
>
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