Hello, John Golitsis: > Jeroen, do you mind if I repost this information to the Digital Home > Canada forums? The same article is being discussed there, but there > are no technical experts on the forums. Of course, that doesn't stop > some from pretending! I don't mind, but first I should make some corrections. Tom Barry: > I don't suppose there exist any very very simple links on how that > process would work? I admit I'm skeptical. None that I know of, but there should be some mention of it in Gerard de Haan's book on multimedia video processing. If only I could find my copy... Anyway, the process of MC de-interlacing is quite simple: you have your odd lines from the current input field and you need to fill in the even lines from history. You still know the result for the previous period, so you have a previous frame. Now if you can move (re-sample) that frame to the current motion phase then you can simply pick the even lines from the previous frame and put them into the current frame. This is obviously a recursive process. It works perfectly if the motion is 2N (incl. 0) lines per period, because then you'll be using only fresh lines from the previous field (and there is essentially no recursion, just weaving). It fails if the motion is (2N+1) lines per period, because then you'll be trying to repeat old information forever. For all other motion speeds you'll use more or less "stale" information. This process depends heavily on the accuracy of the motion vectors, down to a fraction of a pixel. But as the estimation of motion itself is disturbed by interlacing artefacts, this can be tricky. We are seeing other methods coming up, that do not depend on any motion vectors. Faroudja's DCDi was probably the first one. I think it means "Directionally Correlated De-interlacing", or something like that. It is based on the principle that lines are generally not perfectly horizontal, but slightly diagonal. And interlacing artefacts are most annoying on (slightly) diagonal lines. Instead of getting the missing information from previous fields, you can also get it from neighboring pixels in the same field. If you can estimate the angle of diagonal lines, then you can fill in the blanks too. Essentially you are getting vertical information from the horizontal neighbors at different vertical positions, instead of the temporal neighbors. Such intra-field method seems to be easier, cheaper, and more robust than some of the multi-field methods. This is the direction (pun intended) that de-interlacing is taking now. Tom: > Recently I've been becoming gradually convinced that in order to > completely remove aliasing artifacts from, say, 1080i you would > have to vertically filter to only 540 vertical pixels of > resolution. You mean: filtering at the transmitter side, right ? Because at the receiver side you can only filter (scale, etc.) AFTER having done the de-interlacing. That wouldn't make sense. > But if people were really doing that then I'm not sure there > would be ANY additional information available from looking at > adjacent fields, no matter how good or powerful your motion > compensation logic was. And that would even be true for > still scenes. Correct, though you could switch off the filtering for still scenes. Actually, according to Prin, proper pre-filtering of interlaced signals requires a vertical-temporal filter, which will therefore behave differently for moving images than for still images. But, the Generalized Sampling Theorem, like any Super Resolution scheme, depends on there being aliasing (in this case vertical- temporal aliasing) in the individual fields. If there were no aliasing then all fields would indeed carry the same information, and there can be no gain from combining information from different fields (apart from noise reduction). De-interlacing must attempt to resolve the aliases and come up with the original image. On an interlaced display the tracking eye will do this. On a progressive display (or if we need to apply vertical scaling or frame rate conversion) we must do it with algorithms. Indeed a 1080i raster should be more than just two 540p rasters with a different scanning phase. The intra-field vertical aliasing is an essential advantage in order to get more information through. Under ideal conditions 1080i can carry the same information as a 1080p raster, but this can still be disturbed by vertical-temporal aliasing. With a line-on line-off pattern (which is illegal anyway because it is too close to the Nyquist limit) you'll never know whether it was intended as a vertically detailed pattern, or as a 30 Hz blinking frame. That is the essential meaning of "aliasing", that you can not know for certain which one it must be. Luckily these cases are rare enough that in practice interlacing works. (Why send the same information twice - 540p - if you can send additional information - 1080i - instead, I like to say.) Greetings, -- Jeroen +-------------------------------+------------------------------------------+ | From: Jeroen H. 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