DVD Video Scailing, facts and myth?

Discussion in 'Archived Threads 2001-2004' started by Mike Shea, Mar 27, 2002.

  1. Mike Shea

    Mike Shea Auditioning

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    I need a reality check on some things that are confusing me. I am hearing a few different things that don't seem to make sense. These include:

    - Progressive DVD on a native 480p display is better than 480i and a display that scales it to 480p or 1080i.

    - Home Theater PCs sending Dvd signals to a projector running at a native resolution is better than a standard dvd player being sent and scailed inside the projector.

    - A progressive scan DVD player with a native 480p display (like sony hdtvs) is better than a display that scales a signal up to 1080i.

    - DVI is going to be great (assuming the whole HDCP issue gets fixed) because you have digital signals going straight from your dvd to each pixil of your digital display.

    Here is why I am confused. Unless you have a display that is capable of showing a dvd at the exact resolution and framerate it was recorded at, it has to go through conversions. All of these conversions have loss whether they are digital or analog. My understanding is that DVDs have no way of being displayed without conversion within the player even if it is PC based or progressive. It is still being converted from a 480i 60fps signal coming out of the mpeg 2 chips.

    Since conversion has to happen anywhere, the fact that system A is using a progressive dvd player with a native 480p display and system B is using a normal 480i dvd player with the scaling happening in an hdtv that converts to 1080i doesn't really matter. Is this correct or am I missing somethign?

    It seems that with any system, there is a point of conversion and any system is only as good as the quality of that converter, whether it is digital, analog, in the player or in the display.

    I may be missing something here, but aren't we just looking for the best device with the best conversion?

    It seems that the only way our display gets better is with the source material (HD-dvds, dvhs).

    Am I on crack?
     
  2. RobertR

    RobertR Lead Actor

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  3. Bill Slack

    Bill Slack Supporting Actor

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    With the right connections (DVI for instance, or just on a HTPC) then there isn't going to be any loss when scaled, because it can do it on a per-pixel basis.

    Now, there can be image degredation if you're not scaling directly proportionaly (e.g., pixel 1 is repeated twice, pixel 2 3 times... or some sort of interpolation)

    However, if you're just deinterlacing the 480i to 480p and outputting at 72hz you can do it without losing or degrading anything if you keep it all in the digital realm.

    In truth a high quality scaler is likely going to be able to do just as good a job (or better) as a HTPC, but a HTPC can get similiar performance at a tiny fraction of the price.

    And yeah, DVI will be cool that way... but it's all eventually analog anyway. You can't see that much of a difference when viewing from such a small distance. Still, it's a good thing.

    Did you know that CGA/EGA monitors used digital connections? (DVI has just a few more pins...)
     
  4. yekai

    yekai Extra

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    - A progressive scan DVD player with a native 480p display (like sony hdtvs) is better than a display that scales a signal up to 1080i.

    Yes, 480P is the best for NTSC disc.

    I had scaled it to 576P/SVGA/XGA/HDTV and found that the vertical resolution becomes worse.

    - DVI is going to be great (assuming the whole HDCP issue gets fixed) because you have digital signals going straight from your dvd to each pixil of your digital display.

    For DVI, the advantage is that it all done in digital domain from source to display.

    That means a 8x8 pixel letter will be displayed only 8x8 pixels on the screen.
     
  5. Allan Jayne

    Allan Jayne Cinematographer

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    >>>I need a reality check on some things that are confusing me. I am hearing a few different things that don't seem to make sense. These include:
    >>> Progressive DVD on a native 480p display is better than 480i and a display that scales it to 480p or 1080i.
    Generally yes. There are scalers that convert 480p to 1080i with hardly any noticeable degradation and there are scalers that degrade it very noticeably. Progressive DVD on a native 480p display avoids the need for scaling.
    >>> Home Theater PCs sending Dvd signals to a projector running at a native resolution is better than a standard dvd player being sent and scailed inside the projector.
    Hard to say. Depends on the quality of the scaling by the PC vdrsus the scaling by the projector.
    >>> A progressive scan DVD player with a native 480p display (like sony hdtvs) is better than a display that scales a signal up to 1080i.
    Yes, 480p is better off displayed as-is compared with conversion to 1080i although the difference does not have to be profound. With conversion to 1080i, there are always some irregularities with diagonal lines and edges. There are scalers that convert 480p to 1080i with hardly any degradation and there are scalers that degrade it very noticeably. A common problem with scaling of analog inputs from 480p to 1080i is not breaking each scan line up into enough pixels. DVD is natively 720 x 480 but to avoid softening, the scaler must cut up an analog 480p input into more than 900 pixels. If the incoming video is digital, it must be worked with using the same number of pixels per scan line during the conversion to more scan lines. After that, any horizontal scaling is done for further digital processing, or no horizontal scaling is done for further analog processing.
    >>> DVI is going to be great (assuming the whole HDCP issue gets fixed) because you have digital signals going straight from your dvd to each pixil of your digital display.
    If the display dimensions in pixels matches the source, everything is fine. Otherwise it still depends on what scaling choices are provided and also the quality of the scaling. Also if the DVD player DVI output is 480i and the TV doesn't have that good a de-interlacer, the results won't be so good. There may also be shortcomings such as having to watch letterboxed movies as a small picture in a 16:9 screen with black on all four sides, if there are not enough choices such as zoom which may be done via scaling.
    >>>Here is why I am confused. Unless you have a display that is capable of showing a dvd at the exact resolution and framerate it was recorded at, it has to go through conversions. All of these conversions have loss whether they are digital or analog.
    Yes, if the display doesn't match the input in scan lines or rows of pixels, scaling is needed.
    >>> My understanding is that DVDs have no way of being displayed without conversion within the player even if it is PC based or progressive. It is still being converted from a 480i 60fps signal coming out of the mpeg 2 chips.
    Scaling is not absolutely needed here. Getting from 480i to 480p can be done extremely wellm, even by an external de-interlacer.
    >>>Since conversion has to happen anywhere, the fact that system A is using a progressive dvd player with a native 480p display and system B is using a normal 480i dvd player with the scaling happening in an hdtv that converts to 1080i doesn't really matter. Is this correct or am I missing somethign?
    The native 480p system is theoretically better. Also the results will be even worse if in system B the 480i is upscaled first as if it were 240p and then converted to 1080i as opposed to converted to 480p first and then upscaled to 1080i. On 480p the scan lines may be visible while on 1080i the scan lines are probably not visible. The TV can display 480p as 960i (no scaling needed) to hide the scan lines.
    >>>It seems that with any system, there is a point of conversion and any system is only as good as the quality of that converter, whether it is digital, analog, in the player or in the display.
    Yes.
    >>>I may be missing something here, but aren't we just looking for the best device with the best conversion?
    Yes but finding it is not easy.
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  6. Mike Shea

    Mike Shea Auditioning

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    Allan, thanks for the great reply.

    Given those facts, are there any "best of breed" combinations of progressive dvd players and widescreen displays? Any progressive dvd players to avoid based on bad scaling? Any widescreen displays to avoid based on their conversion of dvd inputs?

    Thanks!
     
  7. Marc Rochkind

    Marc Rochkind Second Unit

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    To add to the previous excellent replies:
    The interlaced/progressive conversions apply to the vertical dimension. There is also ALWAYS scaling going on in the horizontal dimension.
    This is because most DVDs are, natively, 704 by 480 (1.47:1), which matches neither 4:3 nor 16:9. (So, the idea that widescreen is anamorphic and fullscreen is not isn't really true; both are geometrically distorted.)
    Pixels can be displayed exactly, with no scaling, only if the display device has non-square pixels--.909 by 1 for fullscreen, and 1.212 by 1 for widescreen. There is no such display, to my knowledge.
    But, as mentioned in the thread, it is better to do the scaling digitally, before the image is converted to analog, rather than after. The only way to do this is with an HTPC, as there are no DVD players with digital video outputs.
    Perhaps there is a DVD player with built-in digital scaling in the horizontal direction. I would appreciate it if someone who knows of such a thing could let me know, as I have never heard of one. (But so what... there's a lot I haven't heard of! [​IMG])
     
  8. Allan Jayne

    Allan Jayne Cinematographer

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    Going from digital to analog does not produce scaling in the horizontal direction.

    Going from analog to digital in practice always results in scaling artifacts in the horizontal dimension. The number of pixels for the new A/D conversion must be 25% or more than whatever number of pixels was ever used in the video's past life to make scaling artifacts almost unnoticeable.

    The DVD player should not scale the pixels horizontally to make them square prior to converting to analog to go out the component or S-video jacks.

    Side squeeze to display 4:3 pictures with gray bars on TV sets locked into 16:9 mode, on DVD players and doublers so equipped, ought to be accomplished by making each of the (approx.) 720 pixels across even narrower to all fit in the inner 75% of the scan line, not by scaling the video to fit on the inner 540 pixels assuming 720 all the way across. This is done during D/A conversion. I am told that iScan doublers do it the right way, I don't know about the various models of DVD players. Done the right way, there are no horizontal scaling artifacts leaving the DVD player. If there is no further digital processing such as for LCD panels or 1080i conversion in the TV set, the second paragraph does not apply.
     
  9. RyanDinan

    RyanDinan Stunt Coordinator

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  10. Marc Rochkind

    Marc Rochkind Second Unit

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    Thanks Allan and Ryan. What I was saying about scaling in the horizontal direction applies only to fixed-pixel displays.
     
  11. Marc Rochkind

    Marc Rochkind Second Unit

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    Oh yeah... about 704 vs. 720, non-square pixels on the DVD, etc...
    My source is the DVD FAQ (http://www.dvddemystified.com/dvdfaq.html).
    An excerpt:
    For anamorphic video, the pixels are fatter. Different pixel aspect ratios (none of them square) are used for each aspect ratio and resolution. 720-pixel and 704-pixel sizes have the same aspect ratio because the first includes overscan. Note that "conventional" values of 1.0950 and 0.9157 are for height/width (and are tweaked to match scanning rates). The table below uses less-confusing width/height values (y/x * h/w).
    720x480 720x576
    704x480 704x576 352x480 352x576
    4:3 0.909 1.091 1.818 2.182
    16:9 1.212 1.455 2.424 2.909
    (Sorry, formatting of table is messed up.)
     

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