Boy are you guys in for a long post. Enjoy!
Not sure - though it could be that some films are still transferred in 50i telecines, rather than in 25p I guess? Less likely these days I would have thought - especially in Europe where HD gear will have been bought more recently. (Early gear sold in the US was strictly 1080/60i or 720/60p - no 24p modes)
Ok so 50i may be chosen over 25p for some content transferred using older equipment. Sounds reasonable
However - I'm not sure it is really correct to describe a 50i signal derived from a 25p source with no filtering as 50i - as it is not technically an interlaced signal (as it is not compatible with interlaced displays) Instead it should probably be referred to as a 25psf (25 frame progressive but segmented frames)
Duly noted. I will from now on try to refer to 50i derived from an unfiltered 25p source as 25psf and 50i derived from a prefiltered one as 50i.
The "NTSC" juddering as I understand it comes from the 3-2 frame repetition so if viewing on a 50hz this wouldn't be an issue whether 24p or 25p.
No - we'd use 2:2 pull down for 25p rather than 3:2 - so both source frames are displayed for the same number of 50i fields or 50p frames (if you are outputting 1080/720 50p)
For 24p you'd have to do the speed up to 25p prior to 2:2 though - otherwise you'd be in the realms of standards conversion.
My point exactly. The NTSC juddering wouldn't be an issue on a 50hz display.
The biggest problem with 25p carried as 50i comes if it is edited in 50i, and there are edits between fields in the same frame. This shouldn't be an issue if the source itself is a 25p edit, but it could be if the edit has taken place in the 50i domain. (Though it SHOULDN'T...)
This is an interesting point but would it not have the same impact on PQ whether it's stored in 25p or 50i (25psf) when displaying on a progressive display. The weaving process wouldn't have any bearing on the fact that the content was edited in the 50i domain versus having it stored as 25p would it? I imagine editing in the 50i domain would end up sucking either way if it's eventually shown at 50p.
I think there are 3 options here :
25p as 25p
25p as 50i but MPEG flagged as progressive
25p as 50i but MPEG flagged as interlaced
I'm not sure if there is a huge difference between 1 and 2 - but there would be between 1/2 and 3.
The difference between 1 and 2 is the crux of my original post. Based on the comments in this thread it seems pretty clear that if handled correctly number 1/2 should have identical picture quality when viewed on a progressive display leaving other reasons for studios to choose one over the other.
Just so I understand you correctly does number 3 refer to 50i from a prefiltered 25p source?
Some plasmas in the US do a reverse 3:2 then a 3:3 to convert 24p carried as 60i to 72p for display with no judder.
There is a large installed base of interlaced CRT HD sets in the US - so I suspect pre-filtering or playback filtering would be required still.
If a disc in the US had prefiltered 1080i so that it was compatible with interlaced displays I assume that would penalise those with a 1080p display (lower vertical resolution). Would it therefore make sense to rely on playback filtering as and when needed rather than the studio prefiltering it so that 1080p owners (who will soon be the majority) get max quality while compatibility is still maintained with the installed base of hd crts?
I don't know of any commercial dvd that is not derived from an interlaced master. The data contained on the dvd decodes to a interlaced video image.
The video then has to be deinterlaced correctly.
I was under the same impression and to be honest what the "dvd decodes to" is what's most relevant to this discussion and not how the bits are physically stored on the disc.
The flagging on a dvd is there to assist the encoding its not there as a guide to deinterlacing hence all the problems with flag reading deinterlace systems (although I have my doubts as to how widespread this particular issue actually is).
Interesting. I'd heard about there being problems with flag reading but really know nothing about it. I wasn't aware the flag was to assist the encode I thought it was there to help guide the deinterlacing. Perhaps Mr. D you could point me to some relevant info?
If you read the thread you will find reasons as to why 1080p is not the same as 1080i deinterlaced to 1080p...what the actual difference will be on domestic displays is entirely open to conjecture.
If I have understood the thread so far the only reason it would be different is if the 1080i were from a prefiltered 25p source and the 25p native was not.
I'm not actually worried about this issue personally. 1080i deinterlaced will look good 1080p might have looked a little more detailed on very high end 1080p displays , then again given the tolerances on the sort of afordable 1080p panels we will see I doubt there will be much in it.
I take it with this statement you are assuming the 1080i is prefiltered and hence would have lower vertical resolution than unfiltered 1080p?
However field-based video sometimes compresses less well than frame-based video when it comes to temporal/spatial compression systems.
Now that's the kind of info I'm interested in. If it turns out that 25p compresses better than 25psf as 50i or 50i then that's another good reason to just dump the data as 25p on the disc. You could then have the player interlace to 50i and add vertical filtering if outputting to an interlaced display (how hard would this be for the player from a technical and practical point of view?).
However quite a lot of 25p productions are mastered in 25p, then have 50i caption rolls or crawls added. That will be an interesting one...
Not sure I understand this could you explain.
Though 1080i is currently the only practical standard for fluid motion.
Sure 1080/25p is practical for film-effect or film-transfer stuff - with the lower temporal resolution - but as 1080/50p is not yet a viable production system, 1080/50i is the only solution in the 1080 sphere for fluid motion... (Sports, Entertainment etc.)
Very good point! I'm mainly interested in 24/25p sourced content (films and certain TV shows) but this is an interesting technical tidbit nonetheless.
Except that a proper 1080/50i master from a 1080/25p transfer will have a lower vertical resolution, as the interlacing process should have been accompanied by a vertical pre-filter to reduce interline twitter (caused by interlace flicker on fine detail) on interlaced displays.
Sure you can omit the pre-filtering - however if you do, then you are really dealign with 25psf not 50i.
Should 1080i be chosen then it'll be interesting to see whether they go for 50i or 25psf. As mentioned I wander whether performing the filtering on playback if necessary is the best compromise to satisfy everyone?
seems like good news. Sounds like the players deal with interlacing - can they filter before outputting? Anyway, seems ideal.
Given that most people will be using progressive displays to watch hd content it makes sense for progressive to be the default and to have the player do interlacing if required although whether the filtering can be done on the fly may well be a key factor in deciding if that happens.
Yep I've read that one. I'm still not betting on there actually being any 1080p discs though.
I hope they will be but the term is being bandied about by people in terms too unspecified at the moment. I could imagine these people almost making the same sorts of comments if someone passed them a paper on dvds containing 60i with 3:2 pulldown on players that inverse telecine correctly and incorrectly surmising the material is 24p on the discs ( as so many people on here do).
Wait and see methinks.
There certainly seems to be a lot of confusion about the various terminology and dodgy marketing doesn't help.
Well done if you read through all that