Interlacing and channel bandwidth

[ppppenguin]

Originally Posted by old_tv_nut

You can't get unity because the phase of sampling is restricted to the positions of the sampling points. 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.

This would apply equally to both X and Y axes on a sampled system, so resolution is degraded euqally on both axes. It is also a misunderstanding of sampling theory. This works equally well in space as well as time. If you sample a signal using infinitesimal size samples at more than the Nyquist limit the original signal can be reconstructed exactly. This is also applicable to 2 dimensional sampling, as noted by Mertz and Gray in their famous 1934 paper. If the sampling aperture is finite you get a falling frequency response, the exact response depending on the shape of the sample aperture. For example a square aperture competely filling the sample pitch would give a sin(x)/x response with a little over 2dB drop as you approach the Nyquist limit. In the real world it is difficult to put a sharp cutoff optical filter ahead of the sensor so there will be aliasing. This suggests using a sensor with more pixels than needed for your TV system and filtering the output. This is equivalent to using oversampling ADCs. It is also one reason why some of the best SD pictures are obtained by downsampling an HD input.