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Chromakey Question

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Aaron Cadieux
Chromakey Question
on Dec 9, 2009 at 3:43:54 pm

Hello,

I shoot green screens on a regular basis. I currently have some merchindise to shoot on a green screen and had a question. Has anyone ever used an LCD tv with a green matte being played on it as the green for a green screen? Wouldn't that make for a flawlessly lit key? I was thinking of using a 46" LCD tv to use as the green screen on this one. Any thoughts?

-Aaron


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john sharaf
Re: Chromakey Question
on Dec 9, 2009 at 3:55:01 pm

Aaron,

You can key with almost any color, as long as the exposure and saturation is correct. A waveform/vectorscope is very helpful in this determination.

If your scene requires replacing both the background and the inside of the monitor screen you can use two colors, just be certain they are not contained in anything else you photograph in the fireground.

JS



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Aaron Cadieux
Re: Chromakey Question
on Dec 9, 2009 at 4:09:34 pm

JS,

Thanks for your reply, but I think you may have misunderstood my question. I just wanted to know if anyone has used an LCD TV with a color matte on the screen (being played on a source) as the chromakey background instead of lighting a chromakey BG the "traditional" way.

Thanks,

Aaron



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john sharaf
Re: Chromakey Question
on Dec 9, 2009 at 4:23:15 pm

Oh! Now I think you're looking for a problem.

A background for keying has to be a uniform even surface; if the monitor was sufficiently out of focus, thus obliterating the dot and/or line pattern, it would probably be ok, but that presumes your foreground subject is very small (perhaps that's the case).

If you are really intent on finding out, give it a try, but the alternative of making and lighting a 3x5' chroma screen (is your monitor that big?) is easy, cheap and proven technology.

JS





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Todd Terry
Re: Chromakey Question
on Dec 9, 2009 at 4:29:41 pm

Not exactly, Aaron... but close.

And it wasn't an LCD, it was a 42" plasma monitor. This was a few years ago when an LCD that big was pretty much unheard of.

We were shooting an infomercial that sort of had a fake newscast format. We built a set in our studio, which had the monitor behind the "anchorman." The original idea was to roll live graphics and video in the monitor, but quickly found it was a pain in the rear to get the timing right with the talent, and we were constantly re-racking the video (which was being played off of tape) for another take.

So... after a few tries we just fed the monitor a pure green signal instead.... which, yes, turned the monitor into a perfectly flatly lit key screen. And it worked like a charm. In fact, it was probably the best and cleanest key we've ever done here.

So yes... it can be done and I think it's a pretty good idea. Just make sure your monitor and camera work and play well together. A camera that has a clearscan mode might be best (and I think most higher-end cameras do now) just to make sure you don't have any phasing or flickering issues.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Tiago Ribeiro
Re: Chromakey Question
on Dec 9, 2009 at 4:36:12 pm

I must say i became interested in your question, and fully understand the dillema. LCD screens seem to be just great for small sized mattes, i guess.

When i was a kid i shot a little stop-motion using a 15" CRT computer monitor as a green screen =)
i guess that's exactly what u mean, well.. with a "little" more resources =)
More recently I also tried an LCD 21" computer screen for doing matte with a bunch of tiny figure toys, but the biggest problem i encountered was that i couldn't find any color suitable for all of them, so i just gave up.
If course in my case it was just for playing around. CRTs are small and had round reflective screens which wasn't that good, so LCDs, and especially a big one, are somewhat better.

But the main issue, from what i remember from my experiences, is that light was casted from the screen onto the objects, and because the objects were plastic-based, they reflected a lot of the screen light, which caused faded edges and other kind of artifacts thay you may imagine. Anyway, i guess that this could be attenuated by correctly adjusting luminosity, so you don't get it too bright, so i guess it will also greatly depend, of course, on the materials of your objects: if you're used to green-screeing, you should know that reflective objects will be troubling.

Anyway, you'll never know without giving it a try. I would even like to propose you to try it out, and then report back on what problems you encountered, and what ways you found to fix them, because i guess that will become interesting for a lot of people to know.

Good lock on that,

Tiago Ribeiro


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Rick Amundson
Re: Chromakey Question
on Dec 10, 2009 at 12:38:48 am

I have done this trick and it works like a charm. You have 2 options, create a green slide the same resolution as your monitor and turn it into a DVD or run it out of your computer. The compositors in my shop loved it due to it's clean edges and no shadows.

Best of luck!

Best of luck!

Rick Amundson
Producer/Director/DP
Screenscape Studios
Bravo Romeo Entertainment
http://www.screenscapestudios.com
http://www.bravoromeo.com
http://www.indeliblemovie.com


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Mark Suszko
Re: Chromakey Question
on Dec 10, 2009 at 5:13:22 pm

The spill and light reflections could be a problem, but if this is just for shooting really small stuff... Walgreens sells chroma green matte flat poster board about 32 inches diagonal for a dollar fifty a sheet. Craft stores sell bigger ones for not much more. And You can bend that sheet into a limbo curve, and it is cheap enough you won't be afraid to punch a hole thru it for a mounting stick to hold your hero object. If you use the LCD screen, blue might work better than green just because leftover blue spill is not as obvious or obnoxious as green spill is.


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