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How to Test if Blacks are Crushed?

Discussion in 'Other video questions' started by AlexJel, Aug 6, 2010.

  1. AlexJel

    AlexJel Member

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    I recently got a new DVD recorder, and I'm converting some tapes, some of which are NTSC-J tapes so the black level is different from a USA tape. While I have my VCR set up to make the blacks correct, I'm not completely sure that the fixed signal is getting to my DVD recorder for some reason. When I play it back on my TV, it looks like they are crushed, but I have no way to make certain. I know Vegas can do it, but I don't have it and would like a program that I wouldn't have to pay for. Also, I tried Avidemux but I can't figure it out. So if someone could tell me a program, or just test this one video for me I would be incredibly grateful! It's a small video, only 6.9 MB.

    Thanks a lot!
     
    Last edited: Feb 3, 2012
  2. davexnet

    davexnet Active member

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    It's possible that they are; at various points in the video, the data crushes on the
    left, and at other points it crushes on the right (crushed hilights).

    However, without having the source to compare to, this analysis doesn't have much value.
    Perhaps the source already had this problem ?

    I looked at the Histogram in Tmpgenc 2.5. Open the source, select setting/advanced/
    custom color correction (double click).
    Check "show histogram" and step through the video.
     
  3. AlexJel

    AlexJel Member

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    After reading my post, I realized that avidemux wasn't the second program... I can't remember what it was at the moment.

    I don't think the source could have had the problem because it's a factory made tape. The crushing you're describing, is it normal to have crushing sometimes in even professionally made tapes? Basically, should I continue on converting my tapes like this, or should I solve the problem first.

    Tmpgenc says the file is unsupported, and on the splash screen when it starts up says that the mpeg trial portion of the program has expired.

    The source is obviously too big to send (3.23 GB), but if I were to send a short video with various clips from the file, would that be sufficient to see if the blacks are crushed and I should solve the problem, or if I should continue capturing? I would use something like avidemux so it wouldn't re-encode it. I also have a few other NTSC-J tapes that it should be able to be compared to. (If it has the same kind of crushing, it's obviously an error in the recording process, probably with the VCR fixing the blacks.)
     
  4. davexnet

    davexnet Active member

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    Your Tmpgenc mpeg-2 encoding has expired. However, if you download this file,
    extract m2v.vfp and put it in the same folder as the tmpgenc executable,
    you will be able to open the file and look at the histogram.
    http://www.digvid.info/software/m2v_vfp.php

    You started out with an analog tape, and digitized it. The tape being analog,
    doesn't have 0-255 values, but when you first capture it, you want to try to
    capture so that the digitized result doesn't crush either to the left or right,
    or to minimize as much as possible.

    It's similar to hooking up an audio cassette deck to the line-in on the computer.
    If the record level is set too high the audio is crushed (clipped) and it sounds like
    crap.
     
  5. AlexJel

    AlexJel Member

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    Ah, thanks a lot! I got to the point of "custom color correction" but I can't find the show histogram button on the page, only brightness, etc. and "enable filter."

    Is it possible to do that though with a DVD recorder? I understood everything you said, but with a DVD recorder isn't what the VCR outputs is what you get?
     
  6. deak91

    deak91 Member

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    my god !!!! the title itself sounds wrong (How to Test if Blacks are Crushed?)whats wrong with you ???
     
  7. AlexJel

    AlexJel Member

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    ...? I think you need to understand more about photography/videography. "Crushed blacks" are where the blacks in a picture are too deep, therefore leading to loss of detail. It has nothing to do with what you're thinking.

    Also, I don't think that post added anything beneficial to the discussion at hand.
     
  8. davexnet

    davexnet Active member

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    AlexJel, the "show histogram " is not a button, it's a selection .
    See the image here.
    You may be right, that with the DVD recorder your options are limited.
    Have you read the manual to see if there is anything related ?

    [​IMG]

    Uploaded with ImageShack.us
     
  9. AlexJel

    AlexJel Member

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    ...That selection is not there. I'm using the free edition, version 2.525.64.184.

    What should I be looking for exactly in the manual? Options to change the black level? I know there's one for playback, I'm not sure about recording.
     
    Last edited: Nov 14, 2012
  10. davexnet

    davexnet Active member

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    Are you on the wrong screen?
    On my version there is "simple color correction" and "advanced color correction".
    (In setting/advanced)
    If yours doesn't have advanced perhaps you should download the trial of the
    recent version .

    I would look at the record section - if there's nothing there you're out of luck.
    I'm not familiar with these devices, since I don't own one.
     
  11. AlexJel

    AlexJel Member

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    Ah, overlooked that on my part. It's there. I'm looking at this one though and it seems to be different that the other histogram I've seen before on Vegas, I assume that it's crushed if it's too hot and gets cut off at the top? There are usually two thin bars on both sides of each picture. Left are blacks and whites are right? Is there are place it can be cut off?

    I'll look over the manual carefully, see if there's anything there.

    Thanks for all the help so far!
     
    Last edited: Aug 6, 2010
  12. davexnet

    davexnet Active member

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    Usually, left or right is where you want to look. If the spikes look as if they're
    crushed against the sides, it a good sign you've lost that detail. You do have the
    black border on the video, so you'll probably see a thin line on the left at all times.

    The height is the amount of the picture at those 0-255 levels and is not so important,
    more to do with judging the gamma, or the mid range values.

    Crush can be black or/and white. In either case, depending on how bad the crush is,
    you lose detail that was previously visible, either shadow detail or highlight detail.

    I took another look at your clip. The best way to judge it is to compare it to
    the tape. Can you see detail in the shadows (tape) that was lost?
     
    Last edited: Aug 6, 2010
  13. AlexJel

    AlexJel Member

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    Ah, OK, that's why the thin bars are there.

    Yeah, I compared the too and in dark parts it seemed that it was more of a solid black and there was more detail in the tape itself. I didn't find anything in the manual, but I'm going to e-mail Toshiba (the maker of the recorder) and ask if there is a black correcting feature.
     
  14. davexnet

    davexnet Active member

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    I wish you luck with it.

    You could always try capturing into the computer. DO you have a capture card ?
     
  15. AlexJel

    AlexJel Member

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    Thanks. I do, but I cannot find a program to do so. STOIK, WinAVI, PVR Plus, Virtual Dub. All give me some problem, so I bought a DVD recorder. I needed one anyway though, VCRs are becoming impractical in today's day and age.
     
  16. davexnet

    davexnet Active member

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    Now that you mention it, I remember some of your earlier threads.
    It's a shame you never got to the bottom of the capture issue.

    Perhaps you'll have to live with the crushed blacks - it didn't look too bad,
    at least not on that short clip you gave.
     
  17. AlexJel

    AlexJel Member

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    Yeah, it really isn't that bad. I have one more idea, and if that doesn't work I'll just have to live with them.

    The idea being, hook the VCR up to a TV with the correct colors, and once I'm sure they're right, hook up the DVD recorder to the output on the TV. I have no clue if this will work but it's worth a shot.
     

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