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Thread: help understanding V8 compositing behavior

  1. #1

    Default help understanding V8 compositing behavior

    I'm fairly new to Vegas and have a question about how it composites.

    I have a video track that shows a computer display, and I followed the directions on this site to blur out the names shown in one column for privacy reasons.

    However, when the tracks fade in or out -- i.e., whenever their opacity is less than 100%, the blurred-out region shows up brighter than the rest of the image.

    What I have is two tracks, the top track containing a duplicate of the second track, with a mask around the content I need blurred, and a pixelate effect applied to that layer.

    Looks like what is happening is when the tracks are fading, the top layer is getting more transparent, and the second (original) track starts to show through, brightening the region that was masked and blurred.

    Can folks here offer me some suggestions around this? I figure it should be easy to do with compositing settings (right now set to Source Alpha), but haven't been able to puzzle that out.

    Only idea I have is to actually black out the same region in the second track, but that seems very crude. Also I don't see any way to get the masks the same in both tracks....

    thanks!

    monty
    Last edited by mkosma; 04-17-2008 at 05:22 AM.

  2. #2

    Default

    STOP!

    From the results you explain you are getting and the aim of what you are wanting to achieve, I think you are confusing "Masks" as used in Compositing and "Masking" as you can use in Pan/Crop. Right or wrong?

    In any event:

    A] T1 will have the pixeled/blurred info

    B] T2 will have original

    What you need to do is

    1] To Track1 Event apply any form of FX that will obscure the info you wish to disguise. Of course this will now "smoother" Track 2 too.

    2] Open Pan/Crop on the T1 Event and click the MASK option. This in turn will get you the Bezier Masking tools and with these you can DIRECTLY apply a mask to the event surrounding the area you want to work on. Once you "close" the mask off and set your variations, you SHOULD see the Track2 Event appearing. The result should be that the info is now "blurred" or pixeled or whatever, but the rest should be as it was.

    Grazie
    Last edited by Grazie; 04-17-2008 at 07:30 AM. Reason: syntax ordering

  3. #3

    Default

    That's exactly what I did.

    Track 1, where I applied the mask, if played solo, shows just the blurred region, all blurry.

    Track 2, if played solo, shows the full-frame original video.

    When they are combined, everything looks just right -- up until both tracks start to fade out. But during the fade, the blurred out rectangle ends up looking brighter than the rest of the video. My hypothesis is that it's fading by making the video transparent, and adding the two tracks together the blurred region ends up brighter than the rest of the frame.

  4. #4
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    Default

    OK I think I know what's going on, but more importantly I have the solution.
    My problem is in explaining the "why" but I'll have a go.

    Assume the amount of light getting through (ie visible in the preview window/final render) ranges from 0 to 100 (like the % of the compositing level)

    For the masked bit....talking compositing levels...
    When T1 is at 100% ONLY T1 is visible (as 100% of the light comes from T1 and there's no room for anything from T2 to show through)

    When T1 is at 60% the maximum "light" that is shown from T1 is 60%, which leaves another 40% to get through from the track(s) below.

    Therefore:
    If T1 and T2 are both set to 60%, then for the masked area the total "Light" that gets through is 60% (from T1) + (40% x 60%) which is 60%+24% = 84%
    For the area outside the mask the total "light" that gets through is 0% (from T1) + (100% x 60%) = 60%.

    So the masked area has a total luminance of 84% whereas athe area outside the mask is only 60% - hence your brighter area.

    OK. Now for the fix. (Ready Grazie? - it's you who inspired me with this stuff)

    1. Add a track ABOVE these two - a new T1 and make BOTH T2 and T3 children of T1.
    2. Fill T1 with a Solid White generated media.
    3. Set the compositing mode of the parent track to Multiply (Mask)
    4. Do your fades/change you compositing levels on T1.

    Problems solved, I think
    Tim

  5. #5

    Default

    Hmm. This is along the lines I was hoping for - a solution that composites the tracks in the way I want (i.e., mask track overlays 100% without regard to transparency). But this approach seems to make the effect a bit less noticeable, but it's still there. If I freeze-frame on the fade-in or fade-out, I'm still seeing the masked area show up brighter than the neighboring regions.

    The closest I have come was to duplicate the masked track, muting the original video track, and on the duplicate setting the mask to negative. The combination of positive and negative masks works for the most part - however, there are transparent lines showing up around the edges of the mask.

    I thought feathering or anti-aliasing might have something to do with those lines - but no combination of settings got rid of them. I ended up manually increasing the size of the blur mask slightly (one pixel or so in each direction) and managed to obscure most of the artifacts.

    So - not perfect, and very labor-intensive to try to get the masks exactly one pixel bigger in the top track. Must be a better way.

  6. #6

    Default

    T1 Parent - Empty [ Tim, don't add any white . . ]

    T2 Child - Gaussian Blur Event with Bezier Mask

    T3 Child - Full Event: No FX and NO Bezier Mask

    In T1 Track Header Click on "Automation Settings" Icon to bring up Level and Fade sliders.

    I've just added a FADE Point to the end of the PARENT envelop and both kids fade away together. No unfortunate whites or blooms. What IS the issue? Please post a screen grab.

    Grazie

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    Default

    Quote Originally Posted by Grazie View Post
    T1 Parent - Empty [ Tim, don't add any white . . ]
    ......
    That was my first effort - but without any media the level control had no effect. Hence my suggestion of a pure white mask (and my solution does work, after all!)
    What I had hitherto failed to realise is what the FADE control does and how it and the levels control interact.
    Many thanks for bringing it to my attention.
    Tim

  8. #8
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    Default

    Quote Originally Posted by mkosma View Post
    Hmm. This is along the lines I was hoping for - a solution that composites the tracks in the way I want (i.e., mask track overlays 100% without regard to transparency). But this approach seems to make the effect a bit less noticeable, but it's still there
    I'm sorry, but I cannot see this at all. If your are getting this either you are not doing exactly as I am or Grazie is.

    Could you indulge me for a minute.

    Track 2 & Track 3 place the same generated media solid colour (preferably something not at extremes eg R=120, G=120, B=120)
    Now on Track 2 create a bezier mask of any shape.
    Do your fades etc and you'll see the effect you first described.

    Now get rid of those fades.

    Add T1 and make T2 &T3 children.

    (Method 1 - Tim's)
    Add generated media Solid White to track 1, set compositing mode to Multiply (Mask) and apply your fades there.
    You will NOT see the bezier shape appear.

    (Method 2 - Grazie)
    Switch on Automation on track 1 and adjust the FADE controller.
    You will NOT see the bezier shape appear.

    As I see it this proves both methods work.

    If you are genuinely following our instructions (one OR the other - don't try to combine!) and you are still seeing the "brightening" effect o your video, some other optical effect must be coming in to play.

    Any chance you could post samples?
    Fascinating
    Tim

  9. #9

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    Very interesting.

    I created tracks 2 and 3 as indicated, with a 120/120/120 solid color and alpha of 255.

    1. Tim, your method 1 appears to work in this simplified test.

    2. Grazie's method 2 seems to mix the two channels into pure white. I took the "Tim's method" test, deleted the solid white from track 1, reset Track 1 composite mode from Multiply to Source Alpha, and applied track fade envelope to track 1

    I.e., when the fade envelope is at 100%, the resulting two tracks appear added together.

    But -- at least the odd mask effect is not present.

    I attached a veg showing my interpretation of Grazie's approach. Let me know where I went wrong!

    Now -- off to try again with my original footage.
    Attached Files Attached Files

  10. #10
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    Default

    Thanks for the attachment.
    Grazie's method IS working. I think you are misinterpreting how the FADE envelope works (indeed this exercise has taught me this very thing).

    When the envelope is in the middle, the media is 100% opaque and the fade colour is 100% transparent (or 0% opaque, if you like)
    Now, each track has two FADE COLOURs, Top and Bottom (to see/set these colours, right click on the track header and select "Fade Colours | Top" or "Fade Colours | Bottom"
    The default for these is top = white, bottom = black.

    Now as you drag the fade slider (or envelope) UP you reduce the opacity of the media and increase the opacity of the TOP colour (in our example white). At the top the FADE colour is at 100% opacity and the media clip at 0%

    Similarly, as you drag the fade slider DOWN from the centre position you also reduce the opacity of the media but this time increase the opacity of the BOTTOM fade colour.

    This is NOT obvious in our example as we were using a solid colour (which was necessary to demonstrate the masked bit working/not working), but replace with a media clip and you should see what's going on.
    Tim

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