DVD - "Shimmering"

Discussion in 'Archived Threads 2001-2004' started by Martin Rendall, Nov 27, 2001.

  1. Martin Rendall

    Martin Rendall Screenwriter

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    How much shimmering should I expect to see watching the typical DVD?

    By shimmering, I mean the effect it looks like there's rain falling between the camera and the object. Another way of looking at it is that there's random noise showing. If you step frame by frame, you see that it looks like random tiny posterization effect.

    I ask because I've seen examples of it in basically all the DVD's I've tried, including Fifth Element Superbit (but only in some scenes). It's noticeable in scenes with uniform coloured flat darker surfaces, where the camera is stationary. Also noticeable in brick patterns.

    So, is this normal? If it's a result of the digital compression, do some players do a better job of hiding it than others? Or am I the only one with this problem?

    Martin.
     
  2. John Kotches

    John Kotches Cinematographer

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    What are you using for a display, and how far back are you seated?

    This is usually a sign that you are too close vs. the height of the screen and the pixel structure is starting to show up.

    Regards,
     
  3. Martin Rendall

    Martin Rendall Screenwriter

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    I'm using a 40H80, and am sitting about 7 to 8 feet away.

    So this means that the shimmering is expected?

    Martin.
     
  4. John Kotches

    John Kotches Cinematographer

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    Martin,

    Not at the distance you're watching.....

    This was my first guess at the problem.

    I'll think on it some more.

    Regards,
     
  5. Martin Rendall

    Martin Rendall Screenwriter

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    Thank you for the feedback.

    I'm seriously considering returning my JVC-S60 player, and either getting a new S60, or possibly going after something like the RP-91. I just need to figure out if it's the source material, or if it's really the player.

    Could the problem be with my TV, somehow? It doesn't seem likely to me, since I can step frame by frame, and see the "noise" frozen in each frame. That is, there's no shimmering when the image is paused.

    Any other thoughts would be greatly appreciated.

    Thanks,

    Martin.
     
  6. Martin Rendall

    Martin Rendall Screenwriter

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    To answer my own question, I visited a friend with a Toshiba SD-2200 connected to a 27" Wega. I saw the exact same effect. Exact. So I'm convinced it's the DVDs, and not the player (or the TV). I could be that a more expensive player like the RP-91 can reduce the effect, but ... I'm relieved that I don't have to go through another DVD player exchange. Thanks for the help.

    Martin.
     
  7. John Kotches

    John Kotches Cinematographer

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    I wonder if you're really seen a Moire` pattern.....

    Hard to say based on your limited description. This is definitely a case of a picture being worth 1000 words.

    Regards,
     
  8. Martin Rendall

    Martin Rendall Screenwriter

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    John,
    I'm curious to see if we can come to a consensus on what's happening. I know what moire looks like, and this I believe is something different.
    Here's a picture (borrowed from a link previously provided by Phil Iturralde in another thread) which should help me describe the problem:
    http://www.geocities.com/mv_us_2000/50H81_FC9.html
    Specifically, crank up your brightness and look at the wall to the left of the woman's face. Do you see the grainy pattern? Imagine that the grain is random, and that the grain will look similar but "moved around" in the next frame. And moved around again in the next frame. That is, there will still be grain, but the different coloured "pixels" will change shade randomly. When the movie is running at proper speed, the wall will appear to be "shimmering".
    Martin.
     
  9. Todd Hochard

    Todd Hochard Cinematographer

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    Most of that is MPEG artifacting. Consider the example you provided- When the scene was filmed dark, this will tend to increase the appearance of film grain. Film grain, by it's nature, is difficult to encode. Now move to the digital realm. It's a poorly lit, high grain area, that is stationary. The stationary, and thus relatively "unimportant" portion of the scene won't be given a lot of bits during encoding, which tends to further exaggerate the problem.

    So, it's a two-fold problem:

    1. Low-light induced film grain,

    2. being encoded at low bit rate.

    I see it a bit. Then again, I see it at the theater on film, too, just without the "digitization" of the noise.

    If it's very obvious, you might have your brightness set too high. Also, make sure your sharpness control is low, as this will add it's own similar looking noise effect.

    Todd
     
  10. Martin Rendall

    Martin Rendall Screenwriter

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    Todd, you have said what I've been suspecting, but have had trouble articulating. What confused matters for me is that other people claim to have never seen the artifacts.

    It's true I have my Gamma all the way up, but that's because I don't want to screw up by black level by upping the brightness. Like most consumer RPTV's, the black level isn't uniform across the screen. I guess this is the trade off. Perhaps I'll tweak some more... up the brightness a couple of notches, and lower the gamma. Thanks for the great suggestions.

    Martin.
     
  11. Bryan Acevedo

    Bryan Acevedo Second Unit

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    For what it's worth, here is a description of how the MPEG encoding works: (as remembered from one of my CS classes in college)

    You start with a grid, defined by a certain number of pixels high and wide. Let's say you say each square in the grid is going to be 10 pixels by 10 pixels. (In reality, the grid sizes are determined by the image complexity) So then you start with the first square (upper left corner, for example) and encode it's average color as a digital representation. Then you go to the next square, and you encode its color as a delta from the current color. You do this for the whole picture. Now you have just done JPEG compression of the frame. So now this image is taking up much less storage space, because each pixel is not represented, but rather blocks of pixels, and then not the actual values, but smaller delta values. (i.e. it takes less to store a value in binary of 10 - the delta - then it does to store the absolute value of 12345 or whatever)

    [EDIT]

    I just realized that I think the actual deltas that are strred are from one pixel to the next in each square, not the deltas from one square to another. So each square on the grid has 1 absolute reference value, and each pixel in that square is stored as a delta from that reference pixel. Like I said, it is kind of foggy in my mind, but this is basically how it works! Just wanted to make sure I was accurate.

    [/EDIT]

    MPEG uses vector technology to figure out what is moving in the scene. So it takes each JPEG image, and they say they are going to interpolate 3 frames for every 4 frames of motion. This means they are going to only store the 1st frame and 5th frame, and then figure out what the motion is in between to create frames 2, 3, 4. Then what they store in frames 2, 3, 4 are only the instructions to move the objects needed to create the effect of motion. That is why on some lower quality encoding rates, if you pause it, you can see the artifacts from this. But the human brain is not quick enough to notice it when it is displayed for only 1/30 of a second.

    So what happens, is that even though the background is supposed to be stable, the JPEG and MPEG encoding only have a finite set of values they can encode. So instead of a smooth transition, you can see a jump in the values. If you want to see really bad examples of this, look at Digital cable. They use high values for the pixel squares on the grid, plus they don't have a lot of values for the color resolution. Look at things like clouds, or steam in the background - it looks really bad.

    What you are seeing is the "jumping" around of the pixels in the background, because maybe the camera was moving just a little bit, and the vector motion is telling the MPEG encoder that the background is moving. So it is moving something that shouldn't be, or the colors that it is moving it to don't have enough resolution to represent the subtle shading changes.

    This of course, was learned before DVD's were out, and this is what was being used for the internet and multimedia stuff. With DVD's, there are probably new techniques they use (like variable rate encoding within the JPEG image itself, and between the frames, etc.) so some of this may not apply.

    But for the most part, this is how the encoding works.

    Hope this helps (and is accurate!). If anyone has anything to correct, please let me know. But this is what I remember from my classes.

    Bryan
     
  12. Kevin C Brown

    Kevin C Brown Producer

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    This possibly (definately) explains the "pixelation" I and others have seen in Blade, mentioned in another thread!

    Cool.
     
  13. Martin Rendall

    Martin Rendall Screenwriter

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    Bryan,

    Thanks for the excellent description! I'm happy that this mystery has been unravelled.

    Martin.
     
  14. Henry Colonna

    Henry Colonna Stunt Coordinator

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    Yes, thanks guys - this discussion has made this issue so much more understandable.

    I didn't see this effect much until I watched Star Trek First Contact this past weekend (twice.) Coincidentally, the picture used in this example is from that movie!!

    I did turn the brightness and contrast up to about 64. I had to do this because the black uniforms looked like a big black blotch with no definition in the 56-57 range, which is how I had calibrated with Avia. At 64, for this movie, I actually saw the wrinkles and the fabric, not just some black hole.

    I have noticed an increase in detail in other movies, too, particularly Dark City, another very darkly filmed movie (that does NOT seem to suffer from this effect even at the increased setting.)

    I guess I won't fret too much about this problem, even though it effects my favorite movie. You suggest turning brightness/contrast down, and perhaps I will do that and try turning gamma up on the DVD.

    Thanks again!!
     
  15. Henry Colonna

    Henry Colonna Stunt Coordinator

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    I'm holding in my hand a "Director's Cut" of Blade Runner. "The Original Cut of the Futuristic Adventure." It's in a black case.

    I have never seen so much "shimmering" or film grain in my life. I had thought that Star Trek First Contact was bad inside the Enterprise. This movie is so full of this effect that to me it is extremely disappointing and distracting. Almost to the point that I'm again questioning my equipment.

    Does anyone else have this particular edition and can you comment on the quality?
     
  16. Christian Dolan

    Christian Dolan Stunt Coordinator

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    Henry,

    The "Blade Runner-Director's Cut" was one of the first DVD's released. They all looked pretty bad, as most first generations of any new technology will. I suspect you're seeing a lot of shimmering on the shots of the golden high-rises? I have a feeling this has to do with horizontal scanning. A fine horizontal line on the film print may be so small that it sits "in between" two scan lines. As a result, we see it first represented on one scan line, then the next and back again.This makes it appear to bounce, or in the case of fine highlights on a large object, shimmer. Hope this helps.

    -Christian
     
  17. Henry Colonna

    Henry Colonna Stunt Coordinator

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    It's mostly in the darker scenes where the background is brown. Dancing grainy patterns all through the background.
     
  18. PaulKH

    PaulKH Second Unit

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    I'm seeing more and more posts on these forums basically indicating that people are realizing the limitations of a) the encoding process, b) the decoding and D/A conversion process, and c) the display technology. So if we all watch enough we become aware of the limitations. But one thing you guys might do is go to the movie theater. If you think your DVD output has got problems, check out the movie theater display. I'm sure it varies a lot from theater to theater, but the few movies I've seen recently at a couple of different movie theaters made me thrilled with the quality of my home theater. The movie theater pictures were blurry, seemed to have more motion issues than my TV, and my sound is better!
    And I don't see 'hairs' or other crap on the film print on my TV! [​IMG]
    But one thing I'd like to add is that DVD doesn't even come CLOSE to the quality of the free over the air HDTV broadcasts I receive and display!!! If you like picture quality, the investment in an antenna and an HDTV decoder is worth it!
     
  19. Henry Colonna

    Henry Colonna Stunt Coordinator

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    Well, my expectations were just so very high because the world has been telling me how fantastic DVDs are.

    I just got home with the new Babylon 5 CD. For me, this is one of the holy grails, the other being the Twin Peaks DVDs. Eleven/twelve years ago I could not WAIT to have high quality recordings of these shows. As I said in another thread, I would feed SVHS tapes into a Magnavox open box special on a JCPEnny 17" TV...but I digress.

    The Babylon 5 DVD to me, again, is full of "Dot Crawl" or shimmering, or whatever. My heart is broken. The children at the beginning of "In the beginning" look poorly digitized. I am truly shocked.

    Just to see if there had been some sort of equipment problem, I threw my Gladiator DVD back in and went to the tent scenes (that have brownish color type lighting.) Beautiful, very very very slight residual effect that you really have to look to see.

    I just don't understand how they released Babylon 5 like this...
     
  20. Bryan Acevedo

    Bryan Acevedo Second Unit

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