Quote:
Originally Posted by ppppenguin
...Hence the Kell factor of a progressively scanned system using modern techniques should be unity.
I may have overlooked something here. For example unless there is some kind of optical filter before the sensor there can be H and V aliasing. ...
*In doing this thought experiment I was influenced by BBC Research Report 1991/4 "Image Scanning using a Fractal Curve" by John Drewery. http://www.bbc.co.uk/rd/publications..._1991_04.shtml John Drewery had a superb understanding of scanning, sampling and spectra. Back in about 1975 I remember him demonstrating the 3 dimensional spectrum of TV signals (PAL in this case) using some wonderful models that he had the BBC Research Dept workshop make from pieces of coloured PTFE. Nowadays this would have been done by computer graphics. |
The Kell factor relates to how close to unity you can come, even with progressive scan. You can't get unity because the phase of sampling is restricted to the positions of the sampling points. That is, if the details lie exactly on the sampling points, you get full amplitude, but if they lie halfway between sampling pints, you get zero amplitude. The sampling becomes equivalent to a synchronous detector. So, the Kell factor says how close you can come to unity and still perceive a repetitive pattern correctly given that the filtering in the system consists of the sensor spot or element shape, the display spot or element shape, and the human eye optical function. Interlace makes it worse, but it's not unity for progressive.
For a full explanation of 3-dimensional spectra resulting from scanning, I also recommend an out-of-print book by Pearson:
http://www.amazon.com/Transmission-D...n+transmission
08-03-2012, 02:02 PM
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