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  1. Hi All

    I captured an old black and white film using virtual dub, and i would like to correct the picture as its quite dark, i have been messing about with the brightness/contrast in Virtual Dub but cant seem to get a good balance, im sure there are other factors which should be considered, can anyone give me some advice on where to start please? Attached is a short clip without any prior adjustments.

    Many Thanks

    DMS
    Image Attached Files
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  2. You need to capture again with proper proc amp settings. You have crushed all the dark and bright areas and there is no getting back the details that have been crushed.
    Last edited by jagabo; 11th Apr 2021 at 05:49.
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  3. Originally Posted by jagabo View Post
    You need to capture again with proper proc amp settings. You have crushed all the dark and bright areas and there is no getting back the details that have been crushed.
    Hi Jagabo, thanks for the quick reply, i thought that may be the case, is there a flat level i need to be adjusting to? as the film is bright in some scenes and dark in others!

    cheers

    DMS
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  4. Video cameras have a different way they capture dark to light than does movie film. Movie film is designed to be projected through a VERY bright light onto a screen in a big room. As a result, the dark sections of movie film have to be much darker than their video counterpart so that the image doesn't look washed out on the screen. Thus, when you capture film, the shadows are always going to look too dark, unless you use a special camera which has an adjustable "gamma curve" which makes the camera more sensitive to the really dark sections of the film and makes those portions brighter, the same as what happens when projected with a white hot projector bulb.

    When using a normal video camera to capture the result, the trick is to expose for the highlights, while letting the shadows stay too dark. I turn on the zebra patterns on my video camera and adjust the exposure until the zebras almost disappear. Since the overall exposure on the film can change from scene to scene, you want to keep the camera's auto exposure enabled, so the usual trick is to either use the Spotlight function, if your camera has it (most Sony cameras do) or simply use the AE adjustment to subtract a little from the auto-exposure.

    Then, in post, using your NLE, you apply a histogram brightening function which brightens the shadows, while leaving the exposure of the midtones and highlights untouched.

    You NEVER want to let the highlights get over exposed because once you exceed 235 or 255 (depending the luma model used) you have reached pure white, and all detail will be lost forever.
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  5. You can Up the gamma by about 20 units in virtualdub with colormill, that should do it
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  6. Colormill is a great plugin for color, and its gamma adjustment may work, but to do the job right, you would be better off using something which lets you decide how much gain to apply to each section of the histogram. For film, you don't want to touch the darkest pixels, because otherwise the result will look washed out. However, starting with levels of 2 & 3 (out of 255) you want to start gaining quite a bit, all the way through the 30s and 40s. After that you want to taper that gain pretty quickly. There is no science: you have to do this "by eye" on a well-calibrated monitor.
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  7. Obviously, you can make some improvements by adjusting gamma with Colormill or Levels, or by using a knee curve in Gradation Curves. But I would try getting a better cap to start with. Bring the black level up and the white level down using the capture device's proc amp. Hopefully that will reduce the crushing of darks and brights.
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  8. Thank you for your replies, I will give colourmill a try. Just for clarity, the capture was taken from a VHS tape. I think the original film transfer to VHS was poor to start with, I think trying to correct the brightness at the capture stage will be difficult as there are a lot of dark and light scenes in the movie and trying to get level balance is really difficult.

    Thanks again for replying to my question.

    Cheers

    DMS
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  9. Member
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    Originally Posted by DMS View Post
    Thank you for your replies, I will give colourmill a try. Just for clarity, the capture was taken from a VHS tape. I think the original film transfer to VHS was poor to start with, I think trying to correct the brightness at the capture stage will be difficult as there are a lot of dark and light scenes in the movie and trying to get level balance is really difficult.

    Thanks again for replying to my question.

    Cheers

    DMS
    Much better for the dark scenes to be a little too bright, that can be corrected post capture.
    But if they're too dark, shadows are crushed and non-recoverable.
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  10. Originally Posted by jagabo View Post
    You need to capture again with proper proc amp settings. You have crushed all the dark and bright areas and there is no getting back the details that have been crushed.
    Originally Posted by jagabo View Post
    But I would try getting a better cap to start with. Bring the black level up and the white level down using the capture device's proc amp.
    What do you mean by this? I thought we must capture raw AVI at 4:2:2 then do all the adjustments in software afterwards. Are you saying its sometimes better to capture with specific settings and not try and do them in post?
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  11. Once the captured signal is clipped you can no longer recover the clipped part with post processing. What is lost is lost.
    You should therefore adjust the proc amp to keep the luma Y preferably in the 16 ..... 235 range for capturing, which provides some headroom for the luma. You can use avisynth's histogram("classic") for checking.
    In your video sample.avi you have clipped (clamped, crushed) blacks at Y=16 and some clipped whites at Y=255.

    Image
    [Attachment 58538 - Click to enlarge]
    Last edited by Sharc; 22nd Apr 2021 at 04:54.
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  12. So you have to do a clipping analysis before doing a full capture, and adjust so end capture is 16-235.
    What is the easiest way to view clipping in a GUI?
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  13. Originally Posted by agisthos View Post
    So you have to do a clipping analysis before doing a full capture, and adjust so end capture is 16-235.
    Yes, a levels analysis is highly recommended.
    What is the easiest way to view clipping in a GUI?
    For example, load this script in AvsPmod
    Code:
    AVISource("Sample.avi")
    turnright().histogram("classic").turnleft()
    Edit:
    I don't know what proc amp adjustments your capture infrastructure supports. The discussion here might be helpful:
    https://forum.videohelp.com/threads/401349-GV-USB2-Capture-Stick-What-s-In-It#post2615895

    Or if you can't adjust the proc amp for capturing you may try as postprocessing filter something like
    Code:
    Levels(0,1.25,255,0,235,coring=false)
    Last edited by Sharc; 22nd Apr 2021 at 06:52.
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  14. Originally Posted by agisthos View Post
    So you have to do a clipping analysis before doing a full capture...
    You make a few short sample caps from different parts of the film (I do 30 seconds or so at a time), study them, adjust the proc amp, and then capture the complete film.
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    I'm a rank amateur at this, so please correct me if I'm wrong, but can we use the histogram in Virtual Dub to achieve the correct setting for capture, like this?

    - Put VDub into capture mode, choose Video>Preview, display the Histogram (Video>Histogram)

    - Play video and watch the histogram, adjusting Brightness and Contrast to set the levels within the safe areas - up to the red marks (I use Jagabo's Graphstudio method for Proc Amp control).

    A video could be checked by cueing to various points and rechecking histogram and adjusting the levels before doing the capture. If there's obvious differences then very bright and very dark sections could be captured separately.
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  16. You can use VirtualDub's built in histogram but it's a bit tricky -- you lose all spacial information so it can be hard to tell what parts of the picture are out of bounds. For example, the out of bounds area may be the black bars at the left and right of the frame. You don't really care about those bars. I suggest you crop 32 pixels off all four edges to eliminate the edges from the histogram.

    Your earlier sample shows blacks crushed at Y=16. That may be what's on the tape. But it may be that your capture device crushes blacks there. Bringing the black level up while capturing may or may not reveal detail in the dark areas. The white level is too high and crushed at 255. Bringing it down will probably reveal more details in bright areas.
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  17. Thanks for the replies to this, unfortunately Iíve had pc issues and had to reset my pic, my dazzle capture device no longer keeps the audio in sync, or maybe itís the windows audio driver that doesnít work, anyway Iím going to have to work out which way to go next, old windows 7 pc, or try and find a capture device that actually works with w10.
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  18. Hi All

    Me again, finally got my capture device working again, but this time it will only work using AmarecTV, tried everything with Virtualdub and it just doesnt like the audio driver! anway, i have done another test capture and tried adjusting the Proc Amp settings, from what i can tell there isnt a histogram on amarecTV so im having to eyeball it, not ideal as im no expert! Anyway here is a clip attached, is this capture any better?

    Thank you

    DMS
    Image Attached Files
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  19. The black level is way off (the brightest whites are blown out a bit too):
    Image
    [Attachment 58749 - Click to enlarge]


    If you pull it down to full black it gets too dark (ColorYUV(off_y=-42)):
    Image
    [Attachment 58750 - Click to enlarge]


    The original film probably had darker shades that were lost in the telecine. So you might use a compromise setting (ColorYUV(off_y=-25)):
    Image
    [Attachment 58751 - Click to enlarge]


    Pick whatever compromise setting you think looks best.
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