Quote:
Originally Posted by andy
lot of HDTVs do a poor job of scaling NTSC to the TV's native resolution. They tend to overprocess it which gives it a smeared flat look.
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Back in the early days of TV cameras, it was found that they could set the focus of the image on the pickup device (various camera tubes then) a little too sharp, so that the resolution of the image would violate Nyquest sampling theory. A fancy way to say that the scan lines, in the vertical direction, act as a digital sampling system. Like a scan line being like a pixel in the vertical direction. Okay, if you aim the camera at a set of venetian blinds on a window, and the focus is too sharp, you get "alias" effects in the vertical direction. Those look here like wide area dark and bright bands, which don't exist out in the real world at that window.
However, it was found that you can slightly exceed this Nyquist focus limit by about 10%, which will make the image as seen on a TV set look sharper, with only a little bit of aliasing. This is called "Kell Factor".
A few years ago I suggested that this Kell factor could be made use of in downconverting HD to SD resolution, and the place I worked for at the time filed a patent application. But the place hit hard economic times, and I don't think they followed up on the patenting process...
Downconverter boxes should use Kell Factor.