Greenscreen Troubles

Bluewave07

Bluewave07

Active member
Hey Guys,
I'm starting on a big greenscreen project in a few weeks and recently ran some tests on our DIY one...It's really nice about 14 X 12 feet, so we were able to keep the subject well lit and roughly 7-8 feet from the greenscreen. However, upon pulling the key and adding a background we noticed that the footage looked sort of fuzzy.

For foreground elements we used a pole to simulate a balcony railing and the pole seemed to be sort of "jumpy" and fuzzy. Also, the subject looked sort of fuzzy around the edges as well.

I know this is common for DV on greenscreens, but both the fabric and the subject were lit very well and placed far from each other. If you guys can take a look and maybe give me some reasons why it might be so hazy thatd be great!!! Thanks..

EDIT: We also used Andrew Kramers chroma keying tutorial, so the edges have been feathered, masks choked, shrunk, etc...

Also, the overlay is from magic bullet, its not from the green screen problems

http://youtube.com/watch?v=hxZMOInTqSg
 
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no offence, but do you really think a youtube compressed shot is suitable for judging your key?
Was your pole made out of chrome or sth similar?
and why wasn´t it fixed, it was moving around wasn´t it?
please upload sth less compressed, bigger and longer...
 
This is our basic set-up. Two high powered lights on the side, two on the top for the greenscreen. For the subject there was one really heavy light reflected off of a white posterboard onto his face.

Spartacus,
If we had a better way to make the clip available we would use it. The pole is metal..supposed to be used for a grind rail for skateboarding...My initial reaction was that it was reflecting the green light, causing the fuzziness











 
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High powered means how much in your case?
check your "member upload center" for webspace...
the lamps you used look really spoted (simple spot bulbs?) this will create a greenA to greenB gradient, resulting in a lot of differnt greens and thus hard to pull a nice key from... especially with DV... but you said you used the Kramer tutorial, that should normally do the trick...
and so far the scene seems underlit (but maybe thats only the photos), hell - what kind of lights are these?
basic question: did you use (auto)gain for the shots? where you full open?
 
Dont use a reflective surface for your rail. Even if it isnt reflecting the green from your screen, it might be refracting a color from the same part of the spectrum. Use non reflective material. I have been working on a HD feature with a good amount of green screen and compositing of CG elements, and I have had problems with chrome materials. Good luck.
 
Hey guys thatnks for all the comments,

Spartacus,
Im not sure exactly how high powered the lights were...Ill check on that and get back to you...Yup, i know that using simple spot lights will lead to hot spots...I was thinking about putting some light paper towels over the liughts to act as a DIY sort of light diffuser as I had heard that was a cheap substitute. Does that sound legit? Also, Gain was flipped to medium (didnt actually realize that till now) and the Iris was manually fully opened..

dvx,
I think that picture looks fuzzy because its a really crappy hosting mechanism (webshots)..But Ill look over the footage again to make sure

sage,
Thanks. That's sort of what I figured in a way..

Nick,
I'll try that.

Thanks to all.

-Matt
 
Bluewave07 said:
Spartacus,
Im not sure exactly how high powered the lights were...Ill check on that and get back to you...Yup, i know that using simple spot lights will lead to hot spots...I was thinking about putting some light paper towels over the liughts to act as a DIY sort of light diffuser as I had heard that was a cheap substitute. Does that sound legit? Also, Gain was flipped to medium (didnt actually realize that till now) and the Iris was manually fully opened..
Click to expand...
so if you used medium gain, where fully open (most lenses loose resolution when fully open and you also want sharp and clean edges between FG and BG...), had an unevenly lit BG and underexposed slightly ( judging from the pics of your lights) you practically did everything wrong for achieving a clean key ;o)
Just do the opposite and reshoot - your results will be much better...
You may also look at DVmatte, Ultra2 or other keyers dedicated to getting the best results out of DV footage...
Good luck!

PS some people also record the composite signal from the s-video out directly to HDD for better keying results, do a search on that...
 
"PS some people also record the composite signal from the s-video out directly to HDD for better keying results, do a search on that..."

Sorry I'm a noob, can you elaborate?
 
I have never done it, but the reason for doing so is that the analog composite from the S-Video doesn´t subsample (actually it doesn´t sample at all, cause it is analog...) the chroma signal like the digital format DV does. Hence you get the full (analog) chroma information and record it eg as an uncompressed AVI, getting full chroma.
When recording DV (especially NTSC) you only get 1/4 of the original chroma info and thats bad for keying.
I hope someone else can elaborate further here, but I really think you should concentrate more on getting clean footage than changing your recording workflow.
As said you made a lot of mistakes when taping the scene and that resulted in a bad key.
DV is problematic of course, but others (including me)here have pulled it off quite effectively so will you if you further refine your greenscreen and lighting process :o)
And please, I know it is so easy to ask here, but a simple search brought this:
http://www.film-and-video.com/broadcastvideoexamples-greenscreen.html
http://www.digitalproducer.com/2003/12_dec/tutorials/12_22/cw_ckeyphat_tips.htm

I didn´t read through, but they look like some real good starting points.
Greenscreen simply isn´t about changing the BG in scene 9 to a green cloth, rather it is a special, highly technical situation that needs extra consideration and good knowledge of the technical side of video production.
Again, good luck!
 
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Bluewave, I've done numerous shoots with greenscreen. It's all give and take, and you learn a lot by the mistakes you make.

If I was you, I'd do a few different setups regarding the lighting of the greenscreen and of your talent. What program are you using to key out the green? If it is AE, then there's a bunch of ways to get around the noise issue that I see in your footage.

For one, just mask out the pole and it won't have the noise issue on it anymore! That'll save you some time from trying to fix all the green reflection of light.

Also, your wider shots will be harder to key because your subject will be represented by less pixels. The smaller your subject, the less number of pixels representing that person, which means your key will be incredibly hard to pull. The pixels representing that person will also be spilling green onto him/her because it's a shared pixel.

I've found that close ups are much easier to key because the pixels can differentiate much between subject and greenscreen.

One of the ways to get around this is to just mask out your subject on the wide shots and then replace the background. I can go on with more suggestions, but you should try yourself.
 
Hey guys,
Thanks for all the great advice.

Justin,
We are using AE's Keylight. Also, we tried masking the pole but it's kind of a pain because when my arm goes in front of it the mask shows on the arm, so we'd have to adjust the mask alot during the shot.

We have another shot where the subject walks up to the railing and its a frontal view. For this shot we were thinking that we would leave the railing out and instead put in a Photoshoped layer as a railing in post. Is this a good idea, or will it lead to further complications?
 
I heard that if you shoot with the camera sideways for greenscreen you can squeeze more resolution out. Also, try to fill as much of the frame as possible because you can always digitaly shrink it after.
 
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