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Blue Screen Tips Please

Discussion in 'Camcorders, Action Cams & Video Editing Forum' started by russ hirst, Sep 17, 2005.

  1. russ hirst

    russ hirst
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    Hi Guys,

    I am intending to make a short film using the Blue screen background effect and would be grateful for comments on the following please:-

    1 I think Ulead VideoStudio 9 has a Blue screen facility, is this true?

    2 Does anyone have any useful pointers/guides/tips on using this method please?

    Many thanks

    Russ
     
  2. Brian110507

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    Yes Ulead VideoStudio 9 does have the blue screen (or green or red or whatever) option and it is quite easy to use.

    The most important thing about making 'blue screen' movies is that the background must be 100% evenly lit and exactly the same colour all over and there MUST NOT be any shadows at all thrown on it, so what ever you use must be big enough to mount far enough back from the actors to avoid shadow. if you can do that then it should be quite easy.
     
  3. Paul_Maycock

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    I don't know how serious you want to go but if you can beg borrow or borrow indefinitely a light meter to check that your light is even across the entire bluescreen. To make the shot more convincing, try and match up the lighting you are using in front of the bluescreen with the lighting that is going to appear in your composited background. For example, if your key light is on the leftside of the actor make sure any shadows in your composited background have shadows that fall in the same direction.
     
  4. Dear Mr Echo

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  5. Roy Mallard

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    if you are using DV then green actually works better, green is sampled more in DV than blue, so the machine has more info to work with, avoid the selected colour being in your subject (although some programmes have garbage mattes to get round this) also some folk use a soft pink gel on the back light, as this helps to eliminate any spill from the background onto your subject. To do this right you do need to use at least 4 lights, ideally 5 (key, fill back on subject, even illumination on backdrop, either two lights or a single light with a softbox. Some shadows aren't a problem with most suites as you can change the latitude and tolerance of the chroma range up to a wide degree, however crease, folds or seams in your fabric can be a real pain as these often register as black, and as such won't be easily chroma's out.

    If you have photoshop you can paint in chroma areas on some parts of the frame as long as your subject is quite static.
     
  6. Mr.D

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    There are a few mistakes in the dvuser article but in principle its correct. I personally always specify green even for film shoots ( the blue channel in film is also very noisy as it has the largest grain structure and lowest intensity , don't know why he thinks its the sharpest). Minor green articles on the foreground subject are not a problem if you know what you are doing. I've keyed green grass off of greenscreens no problem.

    Don't use a coloured filter to increase seperation or kill spill. Green spill is comparatively easy to remove anyway and coloured filters produce nasty edge artifacts.

    The only downsides to green is that it can wash out skintones but again because the green channel is comparitively robust when it comes to manipulation you can normally compensate the saturation back up.

    If the shot is locked off then shoot it LOCKED OFF. The amount of dumbass cameramen who make small reframing adjustments whilst hanging over the camera never ceases to amaze me. You can reframe and add movement in post all you want without having to track what should have been a lock off.

    If the shot is moving then add some tracking marks to the screen ( crosses are better than dots). Makes sure you have enough to cover the entire move. Make your tracking markers large enough to be visible but not so large that removing them is a major hassle , try and make them keyable: orange , red or even blue).If its a push in make sure you have at least two visible at all times. Also if its a complex move make sure the camera is on a nodal head. It will save a lot of hassle. Don't combine zooms and trucks in the same move if you can help it.

    Shoot a screen correction pass: the green screen from the same angle without the foreground subject in place. This can significantly help in removing imperfections in the backing ( so you don't have to spend ages setting it up) and can improve the key. Shoot a few frames to allow for noise reduction averaging. If its motion-controlled shoot a motion controlled screen correction pass if possible. If its a moving camera shoot enough of the backing to allow the compositor to stitch up a plate with enough coverage for the shot and make sure it includes tracking marks.

    The only important bit of greenscreen is the edge of the foreground subject : as long as its large enough to cover the edge for the entire duration of the shot it doesn't matter if you have obvious ends of the set in frame they can easily be garbaged out in post. Don't have any bright lights firing into the camera though. Flare can break screens easier than anything else.

    Nominally expose the screen , don't overexpose it and don't under expose it.
    Shoot outside with natural light for daylight shots when at all possible but watch for lighting continuity during the course of the shoot ( you might have to change the positioning of the screen over the day to follow the sun).
     
  7. Mr.D

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    Shadows are fine if they are required in the finished shot . You can fake them but it never looks right.
    If you have a green screen that includes the floor and feet of the subject then you need to ensure you treat the shadow as imprortantly as the subject.
     
  8. russ hirst

    russ hirst
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    Mr D et al,

    Your comments are greatly appreciated and will undoubtedly be of enormous help to a first time "Blue/green screener".

    Thank you all again, what a great place this forum is!!

    CHeers
     

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