Greenscreen Type Of Thing

Discussion in 'Digital Video' started by jaguar17, Nov 22, 2006.

  1. jaguar17 macrumors newbie

    Nov 22, 2006
    Hey this is probably a stupid question, but I thought I would ask it since I'm interested in doing it lol. What I want to do is say film a person or something, and than add a different video background on the computer. How is this done??

    Thanks Mitch
  2. speakerwizard macrumors 68000


    Aug 8, 2006
    shake is the foremost compositor on the mac (and linux) but motion (part of Final cut studio) also has limited options. probably a cheaper / open sourse route. compoiting is an art to itself
  3. LukeSkope macrumors newbie

    Jun 21, 2006
    San Francisco
    lol, not a stupid question, but it's not that easy. Well, ok, it's easy to do, but not easy to make look good.

    First, the key filters in FCP are not very good. The Keylight filter in After Effects/Shake is great, and much more useful that the FCP keyers.

    You need to shoot your subject against a green or blue screen. The lighting needs to be EVEN. You need good lighting, shadows will screw up the key, or at least make it harder to pull. You will benefit from a large area, with the green screen covering the wall and floor. Pull your subject as far from the screen as you can, so that their shadows do not drop on the screen and so that the screen color does not spill on the subject.

    Use a key filter to pull the key. if your shooting in a 4:2:0 color space (DV) you won't be able to get a good key considering you've never done it before. There will be green haloing around the edges of the subject. You need a matte choker to eliminate that, and you should make the edges of your subject "blume" to make it look natural. Also, some spill supression will help since likely you will be shooting in a small space and spill is inevetable.

    Then you need to have a shot to composite the key against. The two shots should be shot at the same level and angle so it looks natural. Put the shots ontop of each other in the timeline and vola, a quick and dirty chroma key.

    The more time and research you put into it the better it'll be.
    Check, they have a good keying tutorial that helps if you're shooting on DV, although it's done in AE, not sure what program you're using.

  4. jaguar17 thread starter macrumors newbie

    Nov 22, 2006
    Thankyou both of you, I'll look more into it!
  5. sethypoo macrumors 68000

    Oct 8, 2003
    Sacramento, CA, USA
    Is it possible to edit greenscreen footage on iMovie HD if one doesn't have Shake I have some greenscreen footage and would like to know how to put something behind it.
  6. Spaceman Spiff macrumors regular

    Oct 9, 2003
    Well, you can always buy this plugin for iMovie. There's definitely not anything built in.

    But iMovie '07... Who knows? Wait to see. Could be a feature.
  7. bimmzy macrumors regular


    Dec 29, 2006

    Luke sums it up really. If you're going to shoot on DV you're not going get a good key!
    Well sort of.

    The truth is that DV is as soft as butter when it comes to the colour portion of the image. So if you use any kind of "CHROMA KEY" in DV you'll be disappointed.

    But there is another way……
    If you do decide to shoot on DV, and lets face it a lots of people do because it's affordable, instead of choosing a green/blue screen, you could use a black screen instead. Oh and it really has to be jet black.
    You'll find that the foreground will need to be lit very very very carefully indeed. So avoid dark clothes or objects etc for the subject.

    Once you have you're footage, you could use a programme as humble as FCP or motion to LUMA KEY your image in order to create an alpha channel to which you can add a nice background!
    Because in DV video the Luminance ( black and white information) portion of the signal is relatively sharp compared to the colour portion, and therefore possible to get acceptable keying.
    It will take some experimenting at shooting and in post to get it right though.

    Good luck
  8. Macnoviz macrumors 65816


    Jan 10, 2006
    Roeselare, Belgium
    I think FCE is a better option considering it's only a portion of the cost of FCP.

    I don't think their keying differs that much. I've done some keying in FCE and the results were good enough for me (although my standards are maybe lower than yours)
  9. Sdashiki macrumors 68040


    Aug 11, 2005
    Behind the lens
    if you light a scene for DV like you would for film, youll get a good key.

    way more light than youd ever think youll need, and youll get a good key.

    even with FCP.

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