Matthew Garrett

It does work, that's what the 3D comb filter is for; it already knows from the source format what the limits of the signal frequencies are and clamps the output to the same frequency. For discrete moving images like a video stream you set up a 3d matrix that has the lowest common multiple of elements in each respective dimension. You then calculate the interpolation points for each and then extract just the vectors needed for the target resolution / frame rate. Obviously with the wonders of mathematics you only need to calculate the "taps" that you need for those target vectors, this saves computation. To prevent aliasing you can use a finite impulse filter to act as a low pass filter; this has the advantage of doing the interpolation for you and also allows you to calculate only the necessary tap points. If you have a known set of inputs and (in the case of a LCD TV) one known output format you can easily wire this up in an ASIC.