21-06-2017, 05:59 AM
That Kell Factor “fudginess” comes out in the NTSC (1st) deliberations as recorded by Fink. Initially the pertinent NTSC panel chose 441 lines, the 6 MHz channel width and 4 MHz vision bandwidth being givens. But Fink himself took a second look and recommended 525 lines, which was accepted. Whilst equal vertical and horizontal resolution was a nominal goal, it was known that there was a reasonable amount of latitude either way in which picture quality remained acceptable. 525 lines provided a flatter field than 441 lines, and was preferred on this basis even though it resulted in a horizontal definition that was not quite equal to the vertical definition, but nevertheless within the acceptable range.
Fink didn’t refer to the Kell factor as such, but noted that opinions varied as to ratio of vertical resolution to the number of active lines, over the range from 0.5 to 0.9. Basis his own experience, he used 0.8, but acknowledged that values such as 0.64 and 0.7 has been recommended by other researchers. The 0.8 factor pointed to a video bandwidth of 4.78 MHz for equal horizontal and vertical definitions in a 525/60 system. So, avoidance of lininess took precedence over definition equality. (NTSC video bandwidth started out at 4 MHz, but was increased to 4.2 MHz when colour arrived.)
Cheers,
Steve
Fink didn’t refer to the Kell factor as such, but noted that opinions varied as to ratio of vertical resolution to the number of active lines, over the range from 0.5 to 0.9. Basis his own experience, he used 0.8, but acknowledged that values such as 0.64 and 0.7 has been recommended by other researchers. The 0.8 factor pointed to a video bandwidth of 4.78 MHz for equal horizontal and vertical definitions in a 525/60 system. So, avoidance of lininess took precedence over definition equality. (NTSC video bandwidth started out at 4 MHz, but was increased to 4.2 MHz when colour arrived.)
Cheers,
Steve
