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Green/Blue TV Screen


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#1 Ernie Zahn

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Posted 18 March 2008 - 11:04 AM

Hi, I'm going to be shooting a sequence that will feature a television with a superimposed image on it. If the camera were still and directly in front of the TV, this would be a simple effect. But there will be panning in this scene so green or blue screen is the way I'll need to go. My goal is basically to put an image on a TV screen that isn't actually there. I'm doing this because a) a superimposed image will look much more defined and B) because the image that will appear won't have been shot and xfered on the by the time I'll do the TV screen shoot. There are three possible ways I'm thinking of doing this:


1) Have a TV screen set on auxiliary or AV channel that will simply be a blue screen. My worry is that it will still flicker.

2) Have a video of a solid blue/green color playing on the TV running at 24fps. But will it flicker because it's still NTSC?

3) Have a blue or green mat over the TV screen. This would be what I'd do if the first two won't work.

Suggestions? Is there a fourth method?
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#2 Scott Fritzshall

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Posted 18 March 2008 - 12:26 PM

You generally don't need to use "greenscreen" techniques for screen replacement shots. Just shoot with the TV off, so that you get the real reflections, which you can then composite back on. You'll need to do a 4-point track in order to add your new image to the screen, so make sure all four corners are well-defined.
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#3 Alessandro Machi

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Posted 18 March 2008 - 12:43 PM

I think method 3 is the best of the three options.

Or if you use an LCD screen with a television facade over it then the blue output of the screen might work fine. I suppose even if you figured out how to balance the LCD color and brightness and therefore use the actual video during the shot, the odds that the timing will be right aren't that high.
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#4 Michael Nash

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Posted 18 March 2008 - 03:56 PM

You'll need to do a 4-point track in order to add your new image to the screen, so make sure all four corners are well-defined.


I gaffed a music video that used the corner tracking marks to add in the screen image. I had nothing to do with the FX, but I'm guessing they had to do some roto where subjects ovelapped the screen. In those cases I think a complete green screen material (with well defined corners) could have been more helpful.

You can see the end result here: http://www.michaelri...he_matches.html

Why is this question in the "Super 8" forum? http://www.cinematog...hp?showforum=72
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#5 Scott Fritzshall

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Posted 18 March 2008 - 05:03 PM

If you've got a whole lot of detailed stuff crossing the screen then you might start to consider some sort of greenscreen. The benefit of not using greenscreen is that it lets you get the real reflections, which really help to sell the comp. Plus, you don't need to worry about dealing with green spill. The compositing in the video you linked looks pretty good. They clearly had to do a bunch of roto, but that's fine.
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#6 Michael Nash

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Posted 18 March 2008 - 05:11 PM

Green spill isn't a problem from material placed right on the screen. I worked on a feature where we did a LOT of screen/poster/signage replacement with green material on the set, and then tracked in Flame. A piece of green material in ambient set lighting doesn't kick back green light like an entire green stage does. Unless you're using that horrible, horrible bright yellow-green "digi" green stuff! I don't know who ever thought that was a good idea...
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