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Thread: Green screen : background bleeds through on to Blue puppet

  1. #1

    Question Green screen : background bleeds through on to Blue puppet

    Hello all,

    I'm using Adobe Premiere 1.5.1 on Windows XP. I shot some video in front of a green screen recently using my Elmo and Grover puppets. Elmo is bright red and Grover is bright blue. I then imported the video in to Premiere and applied the Green Screen Key video effect to it. I am using a JPG image as the background to test the Green Screen effect. The problem I'm having is that some of the background JPG bleeds through on to Grover, but does not affect Elmo at all. On Grover, the background image appears as a very light ghost on top of him. However, if I put Elmo in to the same position as Grover is, there is no bleed through at all. Any suggestions as to how I can fix this?

    Thanks.

  2. #2
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    Sounds like the lighting on your greenscreen and puppets is not the best it could be.

    However, probably your biggets 'probelm' is that you're trying to do it in Premiere Pro. Does the green screen effect have an option to show the mask thast is being generated? If it does then have a look at it and you'll find it is mostly dark grey and not black. Look for settings like 'despill' to help improve the edges.

    However, if you have access to After Effects (if you stay Adobe) then that is a much better tool for this kind of work and you'll have much better control over this type of problem and be abel to get a very good effect.

  3. #3

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    Quote Originally Posted by Alan Mills View Post
    Sounds like the lighting on your greenscreen and puppets is not the best it could be.

    However, probably your biggets 'probelm' is that you're trying to do it in Premiere Pro. Does the green screen effect have an option to show the mask thast is being generated? If it does then have a look at it and you'll find it is mostly dark grey and not black. Look for settings like 'despill' to help improve the edges.

    However, if you have access to After Effects (if you stay Adobe) then that is a much better tool for this kind of work and you'll have much better control over this type of problem and be abel to get a very good effect.
    You hit it right on the nose. The green screen appears as a very dark grey background in the foreground video, even if there is no background video or image. How can I solve this with proper lighting? Would it help to put a bright light directly focused at the green screen, pointing upward, and behind the subject(s)?

    I'll take a look for a despill option. I was hoping there would be some kind of "saturation" setting which would effect how lenient the program is in determining what is part of the green screen and what is not. The logic being on my part that I could get Premiere to generalize more broadly as to what is green and what is not, and be more effective at determining what is part of the foreground video and what is not. I tried all the threshold and transparency settings on both the foreground and background video, but none of that helped.

    I'd try "After Effects" but I'm doing this just for fun and that program has a hefty $999 USD price tag. LOL. They took it down a dollar so it wouldn't be $1000.

    Thanks for your help.

  4. #4

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    You need to have an even spread of llight across the green screen. Have a light (flood) either side of the screen crossing each other, the light on the left lights the right of the screen and vise versa.
    Look at the screen carefully when lighting it and look for spots of bright light or areas of darker shadow. Ideally get a spot meter to check the levels of light all over the screen. It's not ideal but in conditions that aren't perfect diffusion paper may help here.

    Light the subject seperately, and have them far enought away from the screen so as their lighting doesn't affect the screen or cast shadows on it. Also have a backlight shining on the subject(s) from behind them (above the screen). If you still get spill try putting a magenta gel on the backlight.

    One in Premiere selcet mask only in the green screen effect controls, adjust the threshold and cut off sliders until (as Alan says) the background is perfectly black and the foreground is perfectly white.

    If you still can't get it, some more advanced keying tools allow foreground and background colour correction, this can be done in Premiere. Place an auto colour effect above and below the the key effect, disable the one below temporarily and adjust the other until you have your matte correct. Then unselct mask only, enable the auto colour that was disabled and use it to adjust your foreground colour back to normal.

    If you still can't remove the spill, look for a thrid party despill plug in or reshoot with the proper lighting.

    David.
    Last edited by david walsh; 05-14-2007 at 08:20 AM. Reason: grammer reasons

  5. #5
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    You could also try using Chromakey or Colour Key and see if they do any better. They both have additional tools that Green Screen doesn't have. They have a little eye dropper which will allow you to select the background green screen. Also green and blue are very close to one another on the colour spectrum and it may be difficult for certain applications to distinguish between them.

  6. #6

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    Thanks for your suggestions everyone. They have been very helpful.

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