DVD transfers inconsistent--why?

Discussion in 'DVD' started by jim.vaccaro, Jul 26, 2005.

  1. jim.vaccaro

    jim.vaccaro Second Unit

    Joined:
    Jun 27, 2005
    Messages:
    425
    Likes Received:
    0
    Here's one thing I don't understand about DVD: how can some DVD titles look absolutely perfect, whereas others will have "edge enhancement", pixelation, moire effects, jagged edges, shimmering, and other nasty problems?

    I mean, this is supposed to be digital video, right? Isn't there one standard for how film is transferred to DVD? Shouldn't all studios be able to consistently produce "reference" DVDs? I don't get it. Can anyone explain?
     
  2. RobertR

    RobertR Lead Actor

    Joined:
    Dec 19, 1998
    Messages:
    9,708
    Likes Received:
    172
    Why is the food excellent at a restaurant one day and so so the next? Why is one car reliable and another of the same make a lemon? Why does a football team play great one day and bad the next? [​IMG]
     
  3. ChristopherDAC

    ChristopherDAC Producer

    Joined:
    Feb 18, 2004
    Messages:
    3,729
    Likes Received:
    0
    What does "digital video" have to do with it?

    A telecine of film-video transfer device is an exceedingly complex item of apparatus, electrically, mechanically, and optically; since every reel of film run through it is different, it has to be adjusted differently for good results every time.
    Once you get past the actual transfer, you have compression and encoding. If you had any idea how MPEG-II works, you wouldn't be wondering how some films look so bad, but rather how any of them manage to look so good! The compression process throws away almost all of the information from the original video source, keeping only the bare outlines necessary to rebuild a recognisable picture; while it is capable of looking very good, any mistakes in a hundred mysterious steps such as "edge detection", "motion estimation", "block allocation" and so forth can introduce bewildering artefacts.

    DVD isn't magic just because it's "digital". The original Pentium chips were as digital as can be, and they couldn't do long division! Just like anything else, digital processes [particularly ones involving signal compression] require extremely conscientious control and monitoring in order to work well.
     
  4. Scott Kimball

    Scott Kimball Screenwriter

    Joined:
    May 8, 2000
    Messages:
    1,500
    Likes Received:
    0

    It's digital video, but until recently, it was always from an analog source. That analog source varies with filmstock and age, as well as films having substantial differences in content, grain and other noise. All of this means that there is no "automatic" setting to get a perfect transfer.

    Making a transfer is more an art than a science. Do you want to reduce grain in the print due to it being an extra generation old, or do you want to maintain maximum sharpness? You can't have both. There are usually many compromises made to get the "best" quality.

    Edge enhancement is ringing due to over sharpening, which is usually not visible on the small monitors used during the transfer (which begs the question - why don't they use larger monitors?). There are other things that can cause ringing, though.

    Pixellation is sometimes unavoidable, or nearly so, given certain circumstances that are very difficult to compress. One film that has lots of smoke, mist, fire, water may display pixellation, while a film with none of that is easier to compress and it can be avoided.

    Moire, jaggies, etc., are usually present due to the downsampling of a high resolution source to the relatively low resolution of DVD. An anti-aliasing filter can be employed, but it results in a softer picture... so it can be an either/or situation. Pick the lesser of two evils.

    Any translation from an analog source to the digital realm requires compromises. Since all the sources are different, compromises that work well for one film may not work for another.

    It should also be noted that your DVD player has to reconstruct the compressed data on the fly. Many DVD players will introduce artifacts on their own, or make mild artifacts more pronounced. Your display may do the same, adding edge enhancement, etc...

    -Scott
     
  5. David Allen

    David Allen Stunt Coordinator

    Joined:
    Oct 20, 2002
    Messages:
    138
    Likes Received:
    0
    Best solution for now, watch your DVDs on a Progressive Scan DVD player, displayed on a properly calibrated HDTV via component video or HDMI or DVI. Some of the problems you notice may be inherent to interlaced TV.

    The sad thing is, when HD-DVD/Blu-Ray come out, you'd think there'd be less compression needed due to massive disc space. I have a bad feeling the studios would rather fill up that space with extra junk, than dedicate it to picture/sound quality.
     
  6. Shawn Perron

    Shawn Perron Supporting Actor

    Joined:
    Oct 25, 2002
    Messages:
    500
    Likes Received:
    0
    Set your monitor to 640x480. Look at how low resolution that really is. It's amazing the amount of detail they can cram into such a low resolution format. Like someone else said, it's more amazing that we have such high quality dvds then it is surprising we have lower quality ones.

    On the topic of the upcoming HD-DVD releases, in order to faster penetrate the home video market they may unleash the hd-dvd/dvd hybrid disc on us. This would limit each format to a single layer of storage. So that'd be 4.7 gig for a dvd and 15 gigs for a hd-dvd movie. Going back to the days of low bitrate single layer dvds is not a good thing.
     

Share This Page