Latest post Sun, Feb 7 2010 7:14 PM by stu.mccoll. 46 replies.
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  • Fri, Dec 4 2009 2:41 AM In reply to

    • jwrl
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    Re: HD to SD: Which HD format works best?

    Mondo:
    720P50 will not look "strobey". It's frame rate is exactly the same as 1080i50, but with more vertical resolution (720 lines v 540lines).
    Just because a frame is interlaced, it doesn't lose vertical resolution.  1080i50 and 1080p25 are both true 1080 pixel high formats with exactly the same vertical resolution.  If the final SD release is also interlaced, either will give good results.

    On the other hand you will see more strobing from a 25p original than you will get with 50i.  Some people prefer this look as to them it seems more film-like, while others prefer the smoother motion of interlaced video.  It's a subjective call.

    On the other hand if your deliverable must be progressive then for objectively the absolute best results. shoot in a progressive format.  In practice you're not going to see much difference, though.  A deinterlaced 1080i50 downconversion and a native 720p25 one, assuming that the deinterlacing is done prior to downconversion, will look near identical.

    Mondo, if you're talking in terms of input lines to output lines, just remember that any SD format is interlaced.  In PAL you can regard each SD field as being made up 288 lines, and in NTSC, 240 lines.  To convert from HD to SD you should convert alternate lines only on a per field basis.  Thus it becomes either 540 lines to 288/240 or 360 to 288/240.

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  • Fri, Dec 4 2009 3:49 AM In reply to

    • DylanReeve
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    Re: HD to SD: Which HD format works best?

    50p to 50i conversion can pose problems in theory, although I've never seen it in practice.

    In a 50i signal the scanlines are spatially consistant. The lower-field lines record the detail that is pysically below the detail of the preceeding fields - meaning one frame, top to bottom, does in fact contain 576 lines of detail in PAL, although that detail is temporally separated.

    If you were to take a 50p signal, take each full progressive frame and simply squish it into a PAL field, starting at the first line of that field then you'd get a shimmering image where detail jumps from line to line in the interlaced image. Instead as jrwl suggest, you break the progressive frame into suitable parts (every other line of detail, to correspond with the appropriate field ordering in the interlaced signal) before creating a field out of it.

    Like I said - it's a theoretical risk, but not one I've actually encountered with any real 50p to 50i conversions.

    Various systems - including HP Z440 and Z840 workstations Media Composer 2018 [view my complete system specs]

    Dylan Reeve - Edit Geek // Online/Offline Editor // Post Production Supervisor
    Auckland, New Zealand

     

  • Fri, Dec 4 2009 4:56 AM In reply to

    • Red Ochre
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    Re: HD to SD: Which HD format works best?

    Just wanted to suggest that if you have enough money, that you rent the AJA FS-1 for downconversion. While I've never had any problems with the quality of avid's software downconvert, the time saved is imense. The FS-1 should be cheap to rent and will save funds if you think about your time as money and shouldn't be more than one days rental.

    By the way: I personally can't stand interlaced video. I think once you've become accustomed to progressive I think you'll agree. Obviously, if there is any doubt about your clients response - well they pay the bills.

  • Sat, Dec 5 2009 12:33 AM In reply to

    • jwrl
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    Re: HD to SD: Which HD format works best?

    Red Ochre:
    I personally can't stand interlaced video. I think once you've become accustomed to progressive I think you'll agree
    After 43 years dealing with opposing opinions on this, I doubt it.  I believe that it really is just a matter of personal opinion.

    If there is any guide to this at all, it appears that if you come from a film background you will tolerate judders in motion better, and prefer progressive.  If you come from a video background you're less likely to.

    MC 7.0.4 - Asus P6T Deluxe V2 mobo - Intel i7 920 2.66GHz - Windows 7 Ult64 SP1 - nVidia Quadro FX 1800 - 16 Gbyte low latency DDR3 RAM - Internal 8 Tb... [view my complete system specs]
  • Sat, Dec 5 2009 5:09 AM In reply to

    • DylanReeve
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    Re: HD to SD: Which HD format works best?

    I did my basic testing last night... Captured XDCAM HD422 footage to DNxHD 185X, then played out to Digi with a variety of downconverts.

    In brief summary - the realtime software downconvert (switch Project type from 1080i50 to PAL and play out) was not too bad, and seems almost identical to a Transcode to SD 1:1.

    The best SD from my source seemed to be acquired by using the PDW-HD1500's inbuilt downconvert and capturing from the SD-SDI out. Next best was probably E-to-E video through either HDCAM or HDCAM SR (they were about the same). Hardware downconvert from Adrenaline with DNxcel was next best after that. I don't have DX hardware available to test currently.

    More details and samples to follow in the next day or so.

    Red Ochre:
    By the way: I personally can't stand interlaced video. I think once you've become accustomed to progressive I think you'll agree. Obviously, if there is any doubt about your clients response - well they pay the bills.

    It depends I suppose - I am not at all fond of 25 progressive frames. I just don't like the low temporal resolution. 50p is all good. Of course it's all complicated with modern displays (LCDs, Plasma, LED, etc) which are natively progressive displays, but of course they all have the ability to deal with interlaced video.

     

    Various systems - including HP Z440 and Z840 workstations Media Composer 2018 [view my complete system specs]

    Dylan Reeve - Edit Geek // Online/Offline Editor // Post Production Supervisor
    Auckland, New Zealand

     

  • Sat, Dec 5 2009 6:27 AM In reply to

    • Red Ochre
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    Re: HD to SD: Which HD format works best?

    Of course it's all complicated with modern displays (LCDs, Plasma, LED, etc) which are natively progressive displays, but of course they all have the ability to deal with interlaced video.

     

    Hmmm. Good point. I never considered that the nature of my monitor might lead me to favor one over the other. Also, I'm in ntsc and I wander if that plays a part in me favoring progressive, what with the faster frame rate and all.

    Something that intrigues me about this whole thread and some of the responses are that people would find progressive unpleasant. Do you find watching a 24p feature to be unpleasant in the theater or are there technical reasons why one offends and the other does not?

  • Sat, Dec 5 2009 8:45 AM In reply to

    • DylanReeve
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    Re: HD to SD: Which HD format works best?

    Red Ochre:

    Hmmm. Good point. I never considered that the nature of my monitor might lead me to favor one over the other. Also, I'm in ntsc and I wander if that plays a part in me favoring progressive, what with the faster frame rate and all.

    Something that intrigues me about this whole thread and some of the responses are that people would find progressive unpleasant. Do you find watching a 24p feature to be unpleasant in the theater or are there technical reasons why one offends and the other does not?

    Well yeah, 30p (or 29.976, you crazy people) is somewhat better - although in my experience most people are actually looking for the 'film look' when going for progressive (even if it means sacrificing spatial resolution).

    Yes actually I am not a big fan of 24p. It can at times significantly impact of the suspension of disbelief I find - where something starts to look 'wrong' and you find yourself (or I find myself) somewhat removed from the story in the film.

    I can't find a link at the moment, but as I recall from film school the way 24 frames per second was chosen was that it was basically found to be the lowest framerate at which motion felt natural. But this was at a time long before television - and it was the lowest rate that worked in a dark environment, on a large screen. On a smaller screen with more ambient light the illusion is not nearly as effective. 24 fps certainly wasn't chosen for it's asthetic or the fact it looked better than a faster rate - just that it was what worked.

    Modern television (HDTV for example) is carrying well over a hundred years of legacy. The PAL and NTSC colour systems are created the way they are not because they are the best way to do it, but based on a variety of technical limitations that have long since evaporated. Colour television was made the way it was so that it would remain backward compatible with existing black and white signals. And now our HD standards are derived from those standard definition systems to allow for easy conversion. Crazy.

    Various systems - including HP Z440 and Z840 workstations Media Composer 2018 [view my complete system specs]

    Dylan Reeve - Edit Geek // Online/Offline Editor // Post Production Supervisor
    Auckland, New Zealand

     

  • Sun, Dec 6 2009 2:34 AM In reply to

    • jwrl
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    Re: HD to SD: Which HD format works best?

    Sycophant:
    our HD standards are derived from those standard definition systems to allow for easy conversion. Crazy.
    I read a paper in '80s written by an Ampex engineer when HD systems were first being developed.  He proposed a format that would allow easy downconversion to either PAL or NTSC formats, but would be a universal mastering and release format.  I can't remember the details, but I do remember my disappointment when it was not adopted.

    But let's try a thought experiment: visualise a format that runs at 75i, at a nominal frame rate of 37.5 fps.  It would support three native progressive rates of 24p/25p/30p.  Let's not worry about bandwidth, but if you wish we'll define the frame size as 1920x1080 with square pixels.

    Now let's look at existing legacy media upconversion to such a format.  A 24 frame telecine transfer would become 4:3:3:3:3:3:3:3, ie., every 8 frames would be scanned as 25 fields, and become 12.5 HD frames - a much smoother conversion than the existing 2:3:3:2 and its variants in the 30F world.  This results in a true 24 fps transfer, not 23.97 fps or the 25 fps routinely used in PAL.

    A 25 frame transfer would be simplest of all, just a 3:3:3:3 sequence, or in frame terms 2p:2i:2p:2p:2i:2p.

    A 25p over 50i conversion is harder to explain.  Frame 1 would be directly transferred.  A new frame 2 would be built from field 1 of frame 1 and field 2 of frame 2, and the existing frame 2 would become frame 3.  The result would be that the original 2:2:2:2 sequence would become a new 3:3:3:3 sequence.  Again, the result would be a smooth conversion.

    50i and 60i would be the most problematic.  In the case of 50i, each frame pair would need to be converted to a completely new frame triplet, using something like Avid's FluidFilm technology.

    With 60i the frame conversion process would take an existing 4 frames and build 5 new frames.  2 frames would be dropped every minute except the fifth by modifying the relationship from 4:5 to 4:4.  In every fifth minute only one frame would be dropped.  This would result in an effective frame rate of 29.97, not 29.976, but in practice this error being around 200 ppm should be insignificant.  Also no frames would actually be dropped.  This is just a mathematically convenient way of describing the process.

    Since these techniques would inevitably be included in upres processing, opportunities would exist for spatial resolution enhancement as part of the operation.  If downconverting from such an HD original to any existing SD release format is planned the process would be much simpler than current techniques.

    However, my preference would be for a 1080/48p format.  True 24 frame transfers for all the legacy film out there, no interlace issues, and comparatively easy conversion from existing SD to HD and back again...

    (Please excuse a Sunday morning ramble.)

    MC 7.0.4 - Asus P6T Deluxe V2 mobo - Intel i7 920 2.66GHz - Windows 7 Ult64 SP1 - nVidia Quadro FX 1800 - 16 Gbyte low latency DDR3 RAM - Internal 8 Tb... [view my complete system specs]
  • Sun, Dec 6 2009 4:47 AM In reply to

    Re: HD to SD: Which HD format works best?

    1080 48P is good

    1080 60P is better (IMO) if monitor refresh rates are also considered (True 60 none of this 59.97 nonsense)

    Then mathmeticians wont even needs to wake up to come up with a simple way to convert existing legacy SD framerates for a FEW years. (Avid has already done it in MC4)  Wink

    Cheaper cameras as there will no longer be a need to develop for multiple standards.  Huh?

    Cheaper NLE's with less R&D required to maintain 1 standard. Big Smile

    More R&D required to enable recording and playback of significantly more data than at present for top end performance. Geeked

     

  • Sun, Dec 6 2009 7:36 AM In reply to

    • jwrl
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    Re: HD to SD: Which HD format works best?

    AndrewAction:
    Cheaper NLE's with less R&D required to maintain 1 standard.
    Paradise!

    MC 7.0.4 - Asus P6T Deluxe V2 mobo - Intel i7 920 2.66GHz - Windows 7 Ult64 SP1 - nVidia Quadro FX 1800 - 16 Gbyte low latency DDR3 RAM - Internal 8 Tb... [view my complete system specs]
  • Sun, Dec 6 2009 8:19 AM In reply to

    • DylanReeve
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    Re: HD to SD: Which HD format works best?

    Okay now - I've posted the details and sample images from my downconversion tests.

    Downconversion in Media Composer

    Executive summary: All hardware options (including realtime Adrenaline HD downconvert) virtually identical and better than either transcode or realtime software downconversion of HD material in SD project. But all looked pretty good.

    Various systems - including HP Z440 and Z840 workstations Media Composer 2018 [view my complete system specs]

    Dylan Reeve - Edit Geek // Online/Offline Editor // Post Production Supervisor
    Auckland, New Zealand

     

  • Sun, Dec 6 2009 7:37 PM In reply to

    • stu.mccoll
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    Re: HD to SD: Which HD format works best?

    Hey Dylan, thanks for the time you've put into the tests. It's interesting that the best result you obtained came from an external downconvert before ingest into Avid.

    Your description of the Avid software downconvert of "not too bad" is disappointing, but expected.

    I have just assessed another project here that was shot on 720p for 25i downconvert. My comment re the footage is that it "looks OK" and certainly better than the 1080i I had worked with before. However, when I compared it to footage in the same edit suite shot on XDCAM SD, it looked downright lacking in detail!

    I find it disappointing that the best I can say about a show is that it "looks OK".

    I have to ask the question: "Why shoot on HD formats when all we require is an SD master?" I suppose the answer lies in the fact that the new generation of cameras have a price point and size advantage over the old??

    Len, I've added my $.02 over on your thread. Perhaps Avid may just read our discontent and do something about it?

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  • Sun, Dec 6 2009 8:08 PM In reply to

    • gumbycat99
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    Re: HD to SD: Which HD format works best?

    Nice one Dylan, thanks for that. I'm wondering about projects where there is a mix of SD and HD footage - at the moment people are often using SD XDCAM for their main camera and then a small HD camera for second camera. What happens to the SD footage if the project is edited in HD and then output in HD with a hardware downconvert to SD?  That could be the easiest option for output if both the SD and HD quality is maintained.

    (sorry to give you more work...)

    cheers

    Campbell

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  • Sun, Dec 6 2009 8:45 PM In reply to

    • DylanReeve
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    Re: HD to SD: Which HD format works best?

    stu.mccoll:

    I find it disappointing that the best I can say about a show is that it "looks OK".

    I have to ask the question: "Why shoot on HD formats when all we require is an SD master?"

    Someone on Twitter reminded me about the image scaling settings - I had it set to the default rather than best quality when I did these tests. I may try to redo the Transcode and Realtime software conversions again with the best image scaling quality and see it that makes a difference.

    As for why to shoot in HD for SD finish? Well for one thing I'd say future-proofing is a good reason. With HD source material it is possible to recreate the edit in HD at a later date if that's requried (especially valid for TV shows that may have overseas sale potential).

    I've certainly cut HD material (XDCAM HD422 and EX) in with SD footage (XDCAM 50Mb) and never noticed serious differences or anything that looked 'wrong' - but other comments I've seen seem to suggest that conversion in NTSC rates was much more noticable than I've experienced.

    Various systems - including HP Z440 and Z840 workstations Media Composer 2018 [view my complete system specs]

    Dylan Reeve - Edit Geek // Online/Offline Editor // Post Production Supervisor
    Auckland, New Zealand

     

  • Sun, Dec 6 2009 10:26 PM In reply to

    • stu.mccoll
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    Re: HD to SD: Which HD format works best?

    Sycophant:
    I've certainly cut HD material (XDCAM HD422 and EX) in with SD footage (XDCAM 50Mb) and never noticed serious differences or anything that looked 'wrong' - but other comments I've seen seem to suggest that conversion in NTSC rates was much more noticable than I've experienced.

    Dylan, this is the very thing that started my quest for a better HD/SD conversion. We had a show in edit where the in-car cams were HD and the roving cam was a DigiBeta. Since the majority of the show is carried on the DigiBeta, we opted to output as SD. The quality difference between the two formats on output was very noticeable, to the point that this season, we are shooting SD in the cars as well, with far better results. The show airs in Aus, so cannot direct you to any ep for you to evaluate.

    As for future-proofing, this I understand, but when the show is a reality one (as per the one above) with only local interest, that's never going anywhere else and never likely to be recreated in an HD format, that's where my question originates.

    HP Workstations z400(x4) with MC 7.0.4, Win 7 Pro SP1 64bit on all. AJA IO Express on all. MacPro x3 with 10.9.4, 7.0.4 on 3, and 8.3 on the dual Xeon... [view my complete system specs]
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