Quote:
Originally Posted by mark0077
Someone correct me if I am wrong but this is my understanding. 25p is not the perfect outcome from a 25i -> progressive transformation, 50p is, otherwise we would be just throwing away data, not using it in the best way possible.
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Firstly it's generally referred to (although I've seen debate over this before) as 50i, not 25i, so I'm going to stick with 50i
Your understanding of 25 interlaced frames per second is correct though. This means that the image is sampled fifty times per second. If you convert to 25p this effectively means throwing away half of any motion to try and retain sharpness, leading to stuttery motion. Alternatively it means blending two moments in time together, leading to smoother, but blurrier, playback. Imagine converting 50p to 25p and what that would do to any motion in the image. Static portions would still look ok though. It's the same with 50i to 25p.
So for good results (and IMO far more important than any other post-processing) the 50i source should be bobbed to 50p, if it's genuinely interlaced.
Quote:
Originally Posted by mark0077
(unless the top and bottom field are from the exact same time? (take at the same time by the camera and later transformed into interlaced form for some reason), in this case 25p would be the correct output and could be achieved by simply "weaving" the two fields into one frame assuming they were originally recorded at the precise same time).
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There are a couple of cases here. The first is stuff shot on film. The stream may be flagged as 50i but each pair of fields comes from the same frame of film (sped up from 24 to 25fps). In this case the fields should just be weaved together resulting in 25p output as you said.
The second case is for genuinely interlaced material. If the image is static then although the two fields come from different times it doesn't matter because there's no motion. Then the fields can be weaved together.
Ideally want you want from a deinterlacer when converting 50i to 50p (or to 25p for that matter) is for it to weave together static portions of the image, and only interpolate motion.
Quote:
Originally Posted by mark0077
I am sick and tired of having to manually enable / disable de-interlacing for my PAL DVD's, 95 of which are badly marked.
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Couldn't agree with you more.