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

I think I know what Terry was driving at, so I will try to translate.

In NTSC, there are 483 active scanning lines.  Assume that the Kell 
factor is 0.68.  That would mean that the 483 scanning lines provide 
approximately 328 TV lines of resolution vertically.

Horizontally, the active scanning line lasts approximately 52.5 us. 
 That represents 105 TV lines of resolution per MHz per picture width or 
about 79 TV lines per MHz in that portion of the screen that is as wide 
as the screen is high.

So, if one is COGNIZANT of the Kell factor and seeks square resolution, 
one divides 328 by 79 to determine what the horizontal bandwidth should 
be.  The result is roughly 4.2 MHz.

Terry (I believe) is saying that in System A the horizontal bandwidth 
was selected without cognizance of a Kell factor.

TTFN,
Mark



Alan Roberts wrote:

>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.
>
>  
>



 
 
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