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Questions about progressive DVD players and their chips

Discussion in 'Archived Threads 2001-2004' started by Chris PC, Mar 24, 2002.

  1. Chris PC

    Chris PC Producer

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    I'm trying to understand the chips used in progressive DVD players and the effect when watching DVDs.

    I understand how the Sage/Faroudja and Genisis chips are different from one another in their performance. Each chip is a de-interlacer. So what is the purpose of them. I understand 3:2 pulldown telecine that takes 24 fps movies and makes video from it. What makes a DVD player progressive compared to an interlaced player?

    So here is my question:

    What format do DVD's consist of? Are they all video? Are they all progressive? Are they a mixture of both? If I have an HDTV display, why would I care about a de-interlacer? I'm just a little confused about the technology.

    For instance, if movies have always been converted from 24 fps to 30 for video tapes, why have I never seen combing on video tapes?
     
  2. Chris PC

    Chris PC Producer

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    OK, I re-read this:
    http://www.hometheaterhifi.com/volum...e-10-2000.html
    so its coming back to me. I guess I'm just disgusted with the fact that a "progressive" dvd player has to take pairs of fields that are set up in a sort of interlaced way even though originally that were already progressive to begin with and make them progressive again. What a redundant waste but I guess thats how they made it work for interlaced TV's but allowed for progressive as a future option. They sure didn't make a decent industry standard as I understand many DVD's have bad flags!! or don't even have flags!! Gezz. that sucks.
    This part begs a question:
    "The re-interleaving process we've just covered is specific to 24fps film material which is MPEG-2 decoded (as interlaced fields). It's really a matter of putting the right fields together so it's fairly simple. Deinterlacing native NTSC interlaced video material is much more complicated. In such video material, each field is a unique image in time, and in order to be deinterlaced at an acceptable level, it requires getting into motion-adaptive and motion-compensation algorithms to overcome the inherent problems of the interlaced material. There is no best method, and the two mentioned are expensive to implement."
    So I guess what I'm wondering is HOW MUCH DVD material needs to be de-interlaced or "re-interleaved" ?? Are there movies out there now with proper flags? Do movies with proper flags look good as long as the chip sees the flags and follows them, regardless of which type of chip it is? Genesis, Sage/Faroudja? Also, how much material from a DVD movie is video? There shouldn't be any, right? Except maybe extras?
     
  3. Scott L

    Scott L Producer

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  4. John Kotches

    John Kotches Cinematographer

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    I'm sitting here, reading along, and I had to scratch my head when reading this statement from Scott:
     
  5. Chris PC

    Chris PC Producer

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    Yeah, I read the rest and figured it out. So de-interlacing or re-interleaving is necessary because the dvds aren't encoded properly on each dvd and that means poor cadence, bad flags or lack of flags. Really pisses me off that its like that. Having said that, however, it looks like I will favour dvd player with the Sage/Faroudja or Silicon chips. Although, the Genesis chipped RP-91 is an example of a player that doesn't have the best de-interlacer and yet its a well liked player.
    I still get confused as to why I never see combing with interlaced cable and vhs? What about all the movies I have watched on cable and vhs and the interlaced dvds I'm watching now? I've never seen combing and yet, to my mind, it should be there because of the conversion from 24 fps to 30 fields per second. Is it because the resolution isn't high enough? Whatever the reason, its so stupid that we go to "better" technology and trip up on technicalities that make it look worse in some cases. Oh well. I am eyeing the Panasonic CP-72 Sage/Faroudja 5 disc changer that is due out this year. If the video quality is good, then thats a serious candidate for me [​IMG]
     
  6. Scott L

    Scott L Producer

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    John I see your point, thanks. Didn't know about cheaply encoded DVDs.
     
  7. John Kotches

    John Kotches Cinematographer

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    Chris,

    You don't see combing because cable and Videos have already had 3:2 pulldown applied when transferred for transfer via that medium. TV is a 60 fields, 30 frames per second medium, and the available delivery mechanisms of video require a 60 field/30 frame rate.

    What you will see is interlacing artifacts all over the place -- this is conveniently covered elsewhere in that same article.

    Personally, I'm very sensitive to combing, motion judder, jaggies and other artifacts of deinterlacing as opposed to chroma flaws -- but we're all different!

    Regards,
     
  8. John Kotches

    John Kotches Cinematographer

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    Scott,
    That's also the problem with most magazine reviews. If you stick known good material into a player, you get good results... Weird how that works, huh [​IMG]
    I can't speak for everyone else, but I know I learn more when things go awry then when things go perfectly.
    Regards,
     
  9. Don Munsil

    Don Munsil Stunt Coordinator

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    Some general comments on the thread:
     
  10. Chris PC

    Chris PC Producer

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    Right, ok. I'm beginning to understand the unfortunate situation of dvd encoding and decoding. What I also misunderstood though, was how interlaced video works. In order to understand progressive dvd, i need to understand video first.
    So 24 FPS film sources on cable, vhs, dvd(i) or LD have all undergone 3:2 pulldown such that fields that follow one another do not result in combing? To me that means that video is really showing 30 frames per second made up of 2 identical fields per frame (60 fps), right? Meaning 2 identical fields are put together and they present one frame? I'll read that link again [​IMG]
    You understand that when you see how it seems to be done you get confused if you thought it should be done another way, cause in your head, when you learn this stuff, you're kinda designing it yourself as you go along. When you get to a part that is less than ideal, its harder to understand, but alas, interlaced it was when they made it to start with, and it worked that way. Like I said, its too bad they didn't anticipate progressive and set the dvd format up to allow for it in the decoding and displaying [​IMG] Oh well, at its worst, its only distracting in very bad source material and not a problem on good dvd's and not a problem with good de-interlacer chips.
    Its all coming to me now. I know I could just buy one of the recommended players and one of the recommended displays OR, just buy what looks good to me, but like many of us here, I am facinated with the implementation of the technology and I always want to find out exactly how it all works [​IMG]
    thanks for the helpfull info [​IMG]
     
  11. Don Munsil

    Don Munsil Stunt Coordinator

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    Yes, almost every 24fps source is converted to video using 3-2 pulldown. This doesn't result in combing, because you *can't* get combing on an interlaced display. You can't. It's not possible. Even if they didn't use 3-2 pulldown, as for example some VHS tapes used to do (they instead used "repeat every fourth frame"), you still don't get combing. Even if they used 3-3-2-2 pulldown or some other wacky thing, there would be no combing. Combing only results when the two mismatched fields are shown at the same time.
    Keep in mind that while we do speak of fields and frames in video, there really are no frames at display time. Your display and your brain don't match up the fields in pairs, so it doesn't matter that one film frame is shown for 3 fields, and then the next is shown for 2 fields, etc. "Frames" are only interesting in editing, or in doing video captures. When you're watching an interlaced display, there are only fields.
    From your brain's and display's perspective, fields 2 and 3 make a "frame" and 3 and 4 make a "frame" and 4 and 5 make a "frame." It's a continuous sequence of fields, which happen to be interleaved, which allows your brain to do some very sophisticated motion-compensated deinterlacing, and see the whole thing as an approximation of a progressive display.
    Does that help?
    Best,
    Don
     
  12. Chris PC

    Chris PC Producer

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    Thats weird. That doesn't make sense to me. I mean, sure our brain processes stuff, but surely if two fields have objects far enough away from one another in sequence one after another they'd look wrong. What about when I press pause? What the heck is the VCR or LD doing? What is it displaying? It has to be displaying two fields together in one frame because it looks solid and there aren't any combing affect? Are there? Should I look again?
     
  13. Don Munsil

    Don Munsil Stunt Coordinator

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    I guess I don't understand what you don't understand. Movement from field to field is what produces the illusion of continuous motion. If the objects are far away from each other, that produces fast motion.
    Maybe I'm going down the wrong track here, but it seems to me like you're assuming that there is some kind of connection between fields 1&2, 3&4, etc., and there's not. When one field is drawing on the screen, the previous field is long gone. Then when that field is long gone, the next field starts drawing. What you see when you're watching an interlaced display is a sequence of fields, with a short period of black screen between each one. The persistence of vision that enables you to see the images as continuous is a psychological effect, not an effect in the TV.
    You see combing when two fields get combined improperly, and drawn at the same time on the screen. The brain, not having that short black interval, cannot do the sophisticated motion compensation I mentioned earlier, and sees the two interleaved fields as one whole "wrong" image.
    Does that make it any clearer, or am I just confusing things? [​IMG]
    Best,
    Don
     
  14. Chris PC

    Chris PC Producer

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    Well if thats how it works, then I guess I understand.

    But nobody has answered my question. If you only see one field physically being illuminated at one time, and your brain compensates for the fading out of the other field, then what about when you pause? And lets talk about the most basic format, 4 head VHS vcrs, so forget about laserdisc memory or digital signal processing. What are you seeing there? One field or two? I mean, you can advance "Frame by Frame" on VHS to, so whats happening there? Frames? Fields? Fields doubled? Fields put together? I don't believe I've seen combing doing that. I have seen blurred video, but no combing.
     
  15. Don Munsil

    Don Munsil Stunt Coordinator

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    When you hit pause on a VCR, you get two fields repeated over and over. You are still watching interlaced video, so you still can't see combing as such. When the two fields don't match, you get flickering on the edges, and if you look closely, you'll see something that almost, but not quite, looks like combing. What it will look like to your brain is an unstable still, where objects are vibrating back and forth. It's especially noticeable on quick pans, for example, because there is so much movement between the fields.

    On some tapes, you won't see mismatched fields because they don't do 3-2 pulldown, they do repeat-every-fourth-frame. This produces really bad motion judder when the tape is played, but you don't get any flickering on pause or single-step.

    On a DVD player, things are a little different. If the current frame is marked progressive, it will show both fields of that frame, over and over. If it's not marked progressive, it will take just the first field, scale the 240 lines to 480, split that into two fields and show those over and over.

    When you single-step on a DVD player, it tends to lose the 3-2 pulldown and just show you the frames on the disc, using one of the two methods above.

    Does that answer your question?

    Don
     
  16. Chris PC

    Chris PC Producer

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    Yes it does. Thanks. I understand now. I just never relaized that the fields were just thrown together like that. So interlaced video in general, vcrs and tv's have been playing tricks with our brains all this time? Its a conspiracy I tell you! Heh heh. OK. ok.
    I'll have to do more reading, but I noticed that 120 is divisible by both 24 frames per second and 30 fields/60 frames per second. Is this taken advantage of yet? 120 is a pretty high vertical refresh rate though! Mostly only usful for progressive PC monitors[​IMG]
     

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