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Optimizing your greenscreen shots when shooting with the gh2
  • Here are some tips and tricks for optimizing your greenscreen shots when shooting with the gh2.
    Since I have the gh2, I use it side by side with a red one when doing greenscreen shootings for TV Vfx.
    As the gh2 isn´t capable of recording raw and doesn´t have the same lattitude as the red, I figured out the following techniques
    to take the gh2 greenscreen shots to a level where you can really intercut them with the red material on broadcast programs.
    Which I regularily did and do, and nobody ever realized, that that material wasn´t all shot with the red.
    Try this with the 5d MK2 and you´d be completly lost.

    Lets assume you build a little greenscreen set, maybe 5x3 metres, shooting somebody standing in front and on green cloth.
    As money is short you buy no pro greenscreen cloth but just green cloth from ebay or so. Thats fine.

    Try to get the cloth as wrinklefree as possible, some wrinkles won´t be a big problem.

    If you have very dark (Black) shadows on the foor or elsewhere in the greenscreen try to brighten them up with bounced light - styrofoam will do.
    It´s not necessary to get a perfectly even lit screen, just avoid deep black shadows and blown out white spots.

    If you can control the brightness of the screen by adding light with lamps or bouncecards, or subtracting light with black cloth here´s how you can find the perfect sweet spot for the brightness, the greenscreen should have:
    You need a greycard which has a square of 90% white in it and a Kodak Wratten No. 99 Filter. Both together shouldn´t be over 100$ but it really makes the difference.
    Light your actor in front of the screen and the screen itself.
    Set the exposure on your camera.
    Hold the 90 % white card in front of the greenscreen, so it catches the light the actor would usually catch.
    Look thru the No.99 (green) filter. If the the 90% white looks darker green than your greenscreen you have to brighten the greenscreen,
    if it looks brighter try to darken the greenscreen. Your setup is perfect when the 90% white seen thru the green filter looks more or less like your greenscreen. If you´ve done that a few times you get a feeling for it.
    This technique really helps getting an easy good key with gh2 material.

    If you have a lot of action creating lots of motionblur in your image, you´ll get problems. The blur against green gets quite ugly and tends to produce
    black edges. If you can afford Reelsmart Motionblur (an After Effects Plugin), you should double your shutter speed during shooting (1/100 for 25 frames or 1/120 for 30 frames). You´ll get cleaner and sharper motion. Use Reelsmart Motionblur to generate Motionblur on your greenscreen footage right after the keyer before merging with the background. Select "Images are premultiplied" if you encounter fringes.

    I found the following GH2 settings best for me:
    Smooth, contrast -1, sharpness -1, color saturation -1, noise reduction -1

    Always prefer greenscreen to bluescreen, cause the green channel is much cleaner.

    If you are short on light, and you have too much noise in your shot, even if you don´t see it a first glance (zoom in and you´ll find it),
    denoise your shots with neatvideo before keying. It´s the best denoiser by far. In my opinion it gives you the opportunity to push one stop further than you would normally do. Push the iso up to the extend, that you would normally say "Okay thats one step too much, now I see more noise that I can accept" . Using neatvideo gets you back to the quality of one Iso down most of the time.

    Use 5DtoRGB to transfer your clips before compositing. It helps you get a "smoother gamma", saving more color information in dark parts of your greenscreen.

    Although all this works with a unhacked gh2 (I did a broadcast job with it before the hack), using the higher bitrate of the hack greatly enhances your results. I use the 66mb setting.

    Last tip, if you have serveral keyers or keying plugins, always test them all quickly without heavy tweaking on your shot.
    In most cases one keyer will work obviously better than the others, and thats really not always keylight. Choose the one that performed best, and refine.

    Hope that helps you to tackle greenscreen shots easier in the future.
    It´s clear that you can´t follow all that tips in most cases, just try to use as many of them as possible.

    Holger Neuhaeuser

  • 20 Replies sorted by
  • Thanks for sharing your expertize... Al
  • Thanks Holger for the great walkthrough! Any real world comments regarding GH2 4:2:0 for greenscreen? Do your techniques minimize the effects of half colour channel? + high bitrate? Considering that you are intercutting Red for Greenscreen this is very impressive. Can you post any example shots, (even a mock up) of your 'perfect' green GH2 capture? (maybe even an MTS file for us to play with???)

    Cheers,- I do on occasion do green screen and as of yet have backed away with the GH2- not any more!

    Can you post a link for your 90% Greycard,... finding it hard to find on ebay & B&H,... lots of other cards though... :D
  • Thanks Holger. Greatly appreciated. Merry Christmas!!!
  • Hi alcomposer,
    don´t get me wrong 4:2:0 is always a hassle compared to 4:2:2 or preferably more color resolution.
    But it can be tackled. And as the gh2 is the first small camera that is able to produce really sharp and clear video, that persists in addition to 4k downscaled to hd material, its a great option to have a veritable B-cam on set. At least from my point of view.
    I use it mainly to shoot alternative angles to the red at the same time.
    Ans to answer your question:
    5DtoRGB noticably reduces the 4:2:0 problems and it converts the material from yuv space to rgb. After that you can directly optimize color channels in compositing via mild bluring or better with neatvideo denoising, especially in the blue channel.
    If the material goes into compositing in yuv, you need some more back and forth converting before you can do that.
    I will post some example shots later, but at the moment I´m still under nda, cause the movie hasn´t been aired yet.
  • Normally the brightest white on the card is 90% but you should check the specifications.
  • Thanks again @vempire

    Yes- when I have been wishing for 4:2:2 on the GH2 - I have silently been realizing that this itself is not a perfect situation, that really 4:4:4 is needed for easier greenscreen. What I am trying to get at is that the search for 4:2:2 on GH2 is a bit redundant these days as really more is needed, so its best to just get the "best" 4:2:0 we can get! (Not that I would complain if @VK discovered some lovely 4:2:2 tricks...) But simply it's not my main goal in life now...

    When I asked for footage I wouldn't care if it was a Power Rangers figure in front of a green screen... just to see what the footage looks like. No need for 'NDA' material... just a Hello World style of shot.

    Thanks again!
  • Thanks for tips.
  • @vempire Excellent tips!

    I've been shooting greenscreen with the GH2 and found that if you can shoot at ISO 160, by all means do so. Neat Video is of course, an option, but if you can avoid it, so much the better. Noise is very bad because it translates into edge chatter when you pull the key.
  • Your edges will improve a lot, if you denoise red and blue channel seperately while not touching the green channel. Visually all the sharpness you see exists only in the green channel.
  • And blue is worst anyway. Any good denoiser can do separate parameters for the color channels.
  • @vempire
    How would you do separate red and blue channels with Neat Video? Neat works in YUV.
  • @Ralph_B

    Considering that green screen is in a studio environment anyway... Totally agree with your suggestion of getting as LOW as possible in ISO.
  • Sorry, my bad, while it's a great denoiser, it offers no access to RGB. But you can do less denoising on Y and more on U.
  • Hello -

    I've had no problems with green screen in FCPx. I found that if you do more than one sample of the green area you get very good results - even creases are no too much of a problem.
  • Here's a pretty good lighting tutorial by Eve Hazelton I found on Bloom's site regarding shooting green screen and AE.

  • @Vempire
    Thanks a lot, great!!
  • @vempire What patch have you found to be the best for green screen shooting. I am usually shooting 1280x720p 50 on it's side.