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HDTV/HD-DVD: 1080 50/i or 1080 25/p

Discussion in 'Televisions' started by 00fjackson, Mar 24, 2005.

  1. 00fjackson

    00fjackson
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    Provided most TV makers take the sensible decision to capture most (non-sport) content in 1080 25/p what do you think it will be broadcast in?

    If it is interlaced to make it 1080 50/i and compatible with all HDTVs (without processing) some vertical line resolution will be lost (from filtering to reduce line twitter) and it would need film mode detection for the full progressive image.

    However if it is ever going to be broadcast in native 25/p it must be part of the spec to be able to interlace it (for HDTVs which won't be able to accept or display 1080p- (the majoritory at first)) and double the frame (for those which can). Before HD broadcasts begin (FTA terrestrial, not Sky-HD) and decoders are manufactured this must be part of the spec.

    What I mean is broadcasting 1080 25/p must be backward compatible with TVs being sold as HD-Ready (which only have to accept 1080i and 720p) and as soon as the uncontrolled (unlike Sky) market for HD recievers opens up any changes to the broadcast must be backward compatible with all of them.

    With regards to HD-DVD the players will have to be able to interlace 25/p but will they be able to output the pure native signal (doubled)- 50/p? (SD-DVD players always had to interlaced progressive it before optionally reconstructing the frame) If not we will probably be stuck with pre-mixed interlaced again as there is no advantage to anyone to record it progressively as it was all interlaced anyway. Hopefully this will not be the case.

    What does everyone think? :confused:
     
  2. Dutch

    Dutch
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    At the moment they will broadcast 1080p25 shot material in 1080i50. Things may change in 5 years or so when 1080p50 broadcasts might be possible once analogue has given up it's terrestrial bandwidth. I don't think 1080p25 would ever be a broadcast standard.

    As I've said before, I'm sure HD DVD players will allow you to select a suitable output resolution for your legacy display.

    Steve
     
  3. 00fjackson

    00fjackson
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    That's unfortunate, maybe a solution to maintain full progressive vertical resolution would be to transmit an unfiltered interlaced image (still with full res.) and then vertical comb filter it upon reception. This way through de-interlacing we could get the full 1080 25/p image and it would be compatible with all displays without proccessing (albiet with lots of line twitter). :thumbsup:

    Just a thought...

    :smashin:
     
  4. 00fjackson

    00fjackson
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    Of course if the source is 25/p it would not be deinterlaced by film mode detection and unless the source data was carried in the signal, no chip would be able to work out it was sourced from 25/p because not frame would be repeated.
     
  5. Calleva

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    Um, 25P originated material WOULD be detected by film mode detection exactly as it is already on SD material.

    Film originated material uses 2:2 pull down for 50Hz territories or 3:2 pull down for 60Hz territories today, the same principle works in HD as well except slightly different terms apply.

    For 50Hz territories EXACTLY the same 2:2 pull down is used but it's refered to as PsF (Progressive scan Segmented Frame) This is used by Sony on their HDCAM VTR decks (probably accounting for 90% of all 1080 line capable broadcast VTRs)

    PsF can be detected and de-interlaced very easily and has been common-place in HD production for years, you don't even need to detect field dominance in PsF as it is fixed whereas detection of correct field dominance in SD 2:2 pulldown is one of the trickier issues.

    So, the broadcast format 1080/50i can carry fast motion sport as 50i and 'film' as 25PsF without loss of resolution and it is backwards compatible with all display types. There will never be a direct 25P broadcast as there really is no need for it !
     
  6. Stephen Neal

    Stephen Neal
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    However - 25PsF is only a production format (designed to work with existing 50i kit with no major changes). However if you broadcast 25PsF via 50i - without vertically filtering - you'd have real problems with people using 50i displays. Vertical HF detail would start flickering quite nastily at 25Hz.

    Sure you COULD broadcast 25p stuff via 50i at full resolution. However if you broadcast it FOR 50i displays - you'd need to vertically pre-filter prior to transmission - unless you could add filtering to the receiver standard?

    (Of course how many 50i native displays are there going to be??)
     
  7. 00fjackson

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    That's great news- so the HD deinterlacing chips will work for 24Hz (film) and 25Hz progressive source material. Sorry, I had asumed that film mode detection worked by finding that every 24th and 25th frame are the same. It must be lack of motion between interlaced frames, right? :) So as long as they shoot in 25/p and 1080p displays become common then 1080 25/p video is a reality!
     
  8. 00fjackson

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    If it is going to be part of the reciever standard then why not include transmission of native 25/p? I thought of it as an afterthought when it is too late to change the standard. Most 1080i TVs will have vertical line filtering built in and as you say how many will not have that or 1080p (in UK anyway)- maybe just the first few CRT HDTVs?

    Hopefully if capturing 1080p 25 takes off there will be not need for the lesser 720p and if fast moving video needs 50Hz it can use 1080 50/i. :smashin:
     
  9. Stephen Neal

    Stephen Neal
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    I guess it depends whether receivers can "post-filter" 25p material effectively enough when interlacing to 50i - if the material is broadcast as 25p with full vertical resolution?

    I'm not an expert on the processing requirements for decent vertical filtering - though I know that quite a few aspect ratio converters use vertical information from multiple fields to filter to a high quality. It may be that 25p to 50i filtering may not be cost effective "in receiver" at a decent quality level - and HD will require high quality processing?

    I'm not an expert, and I expect 25p to 50i is easier than going the other way.

    It does seem as if 50i displays aren't likely to be widespread, so 25p may make sense. (How 25p/50i signalling and mixed 50i / 25p channels would be managed is an interesting question. Imagine mixing between a 50i station ident and the beginning of a 25p film!)
     
  10. 00fjackson

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    Surely wether it is transmitted as unfiltered 50i or native 25p there is the same processing required. For 50i it must deinterlace (for progressive displays) and filter (for interlaced displays). For 25p it must interlace (for interlaced displays) and filter aswell. Plus it must double the frame to 50/p for progressive displays which will only accept 50/60 i/p.

    If they do include the display of 1080 25/p in the spec then it doesn't seem to me to make any difference whether they must interlace 25/p or deinterlace unfiltered 50i. The real question is if it will be in the standard. If we follow America and its not, then 25/p transmission will not be possible. One possibility for 25/p is the fact that HD-DVD supports it and both HD-DVD and HDTV will arrive at about the same time and people waill want the same quality (whereas in the states HD transmission started years before any pre-recorded format)

    To me it seems unlikely that will ever happen. So much difficulty just for a station indent! It might be another reason for not sending 25/p. The indents would all be 25/p so if deinterlaced when mixed with other 25/p they would work and if filtered when mixed with 50/i they would still work.

    In conclusion I would say that deinterlacing of unfiltered 50/i is more likely than transmission of 25/p.
     

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