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Using Luma key (white background)

1516 Views 21 Replies Latest reply: May 1, 2012 6:26 PM by filmmakersue RSS
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editgal Level 1 Level 1 (0 points)
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Apr 28, 2012 7:06 PM

Hi. I shot a series of interviews against a white background. They look great. Now want to key video or photo using the luma key. It keys ok but when there is quick movement (say of a hand moving) the white is bleeding through. I have struggled with the values to no avail. I have also tried using the choma keyer, which gives me more control but same problem. any fixes or ideas? here is a shot of what i am talking about.

 

  • Garzdubz Calculating status...
    Currently Being Moderated
    Apr 28, 2012 7:55 PM (in response to editgal)

    I have run into this as well.

     

    Hopefully it is a brief movement so the fix will not consume too much time.

     

    Make a copy of the keyed video and apply a 8 point matte around the hand only. Add keyframes to accomodate the movement, keeping the white bur hand inside the matte. Add an additional luma key to this layer and maybe a matte choker or Matte magic filter to reduce the white fringing.

     

    This will shrink the size of the hand but hopefully it won't be nearly as noticable as the White blur.

     

    Copy the 8 point matte filter to the original layer, but set it to matte to invert, that way the hand will not be seen in that layer but will be present on the double luma key layer.

     

    Try different combinations of of softness to get a smooth transition between the 2 layers.

     

    Good luck.

  • Gary Scotland Level 5 Level 5 (7,605 points)
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    Apr 29, 2012 7:07 AM (in response to editgal)

    luma keys are suitable for graphics work; keying shapes or text over a background, not full chroma live action from camera.

     

    Chroma keing is the answer for future work.

     

    Looks like what youv got is the best you will achieve.

     

    But why use a lumakey in the first place?

  • Nick Holmes Level 7 Level 7 (29,805 points)
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    Apr 29, 2012 8:15 AM (in response to editgal)

    >luma key is what i was told would be the best for keying white...

     

    Well yes, because white doesn't contain any chroma information.

    If you look at the image you posted there are white or near white patches on your subject which will result in holes if you go too far or the rough edges you have now by not being able to go far enough.

     

    >...as opposed to chroma which is traditionally used for green or blue screen.

     

    Blue chroma is chosen because it is the least missed color in live footage. A correctly lit and shot bluescreen will give you a very clean key. There are also several other options when using a blue chroma key such as spill filters and matte chokers to help clean up further.

  • Gary Scotland Level 5 Level 5 (7,605 points)
    Currently Being Moderated
    Apr 29, 2012 8:31 AM (in response to editgal)

    luma is indeed best for keying white, for graphics,  not for live moving action in colour.

    This should have been shot with a green or blue background and chromakeyed.

     

    Unfortunatly the chroma keyers in Final Cut and Motion are very poor.

     

    You might be interested in testing dvMatte Pro on your next project just to prove how easy chroma is these days, I used it for a project designed for a giant screen at a conference centre last year. It produced the best keying I have done recently using a software keyer and incredibly easy to use. I usually use Primatte a £2,000 software keyer which sadly is no longer produced.

     

    good luck

     

    dvMatte Pro

  • Gary Scotland Level 5 Level 5 (7,605 points)
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    Apr 29, 2012 9:23 AM (in response to editgal)

    I cant see what you have on your production monitor, but I dont think you can do much more, as has been said luma keying is for a diffferent situation.

     

    how about trying:

    a)

    use your original clip showing the white background, correct the highlights of your white background in colour corrector to stop grey levels appearing. Perhaps crop the picture to a square then lay over another track for  a background. white backgrounds were fashionable a few years ago and I  used this look last year for a picture in picture effect.

     

    b)

    test the dvMatte plugin, it has sophisticated keying filters for the luma signal so it could improve what you have so far

  • Garzdubz Level 1 Level 1 (0 points)
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    Apr 29, 2012 1:14 PM (in response to editgal)

    Sorry it didn't work...

     

    If B-Roll was an option, I sure you waould have gone to a different scene if you could...

     

    Chroma Key Blue is the best for future, but beware of Blue eyes. In that event just put a cmall chunk of cropped video behind the Blue eyes to fill in holes.

  • Jim Cookman Level 7 Level 7 (23,435 points)
    Currently Being Moderated
    Apr 30, 2012 10:51 AM (in response to editgal)

    What is the source footage?  Is it interlaced?  You might try deinterlacing it if it is.  Won't do a heck of a lot but it will help some.

  • filmmakersue Calculating status...
    Currently Being Moderated
    Apr 30, 2012 5:34 PM (in response to Jim Cookman)

    the footage was shot 30 progressive.

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