Lighting for Blue/Green Screen

[Ed Frazier]

I have been asked to record a singer in a lounge/tavern setting. I want to use a blue or green screen background for chroma keying in post and will need to purchase suitable lighting for this. I was considering two quartz lights on the background and one or two on the talent. Can anyone comment on this and/or suggest alternatives.

Thanks
Ed

I saw an unbelievably good article on blue screening for DV at www.2-pop.com I'm not sure exactly where it is but I've got the URL on my "favorites" list at home. When I get to my PC i'll check it out and post it here for you. Or if you have the patience, try to search through their archives. The article will really help you out.
BTW it comes in two parts so look for that too.

[Ed Frazier]

Thanks for the reply. I poked around on 2-pop.com and found the article you mentioned. It will be very helpful I'm sure. The links for the two-part article are:
http://www.2-pop.com/tools/DVGuerillaKeyP1lc.pdf
and
http://www.2-pop.com/tools/DVGuerillaKeyP2lc.pdf
if anyone else is interested in the subject.

[Ed Frazier]

Videomaker Magazine (Nov 2001) has an article by Scott Anderson on unique problems when keying in the DV format due to compression. Can anyone comment on this and recommend work-arounds. Mr Anderson sugggested some, but I would like to hear from others who have experience with this.

Thanks,
Ed

Hi there!

I am planning to buy the new Canon GL 2 (XM 2 in Europe) cam. Now I am looking for every bit of information I can get. I am very interested in the 2 articles mentioned, which should be available at www.2-pop.com. Unfortunately I can not find them on their site. Could someone please give me a correct link where I can find the articles or mail me the two pdf files mentioned above to christoph.seemann@chello.at?

thx
Chris

[Henrik Bengtsson]

well.. some pointers to lighting blue / green screens.

The goal is to get as even green / blue shade as possible and to avoid coloured light to spill onto the subject. So make sure the greenscreen is well behind the subject, and pref. use a shorter DOF so the background green is blurred out . Now. having said that, i must add that this ONLY applies when the entire background is to be keyed. If you have other appliances blurred in the background together with the green you may have keying hell later on.

As for lighting, any diffused light that gives an even smooth light is good. Like i mentioned before, the goal is to get an even smooth green /blue shade without any highlights or such. This also means you should by all possible means use non-reflective materials. Even cloth can be highly reflective.

Place the subject as far from the greenscreen as possible since you will want to avoid any spillovers on the sides. And make very sure the subject is not wearing anything in the same colour range as the green screen. You may think that one is obvious but i've seen people miss that one to many times for me not to bring it up :)

If ever possible, shoot on as low compression as possible, digibeta if possible. You can do a good key even on DV materials, but digibeta is more forgiving.

Oh .. one final tip. Check the smoothness of the green/blue screen area in B/W or by just checking the green channel. It will show up any creases/irreguralities MUCH better than in a colour environment. Your eye tends to blend things together. Especially when we're talking about small changes in shades.

Ok. thats about it in regards to the lighting and shooting of a blue/green screen set. If you have questions regarding the actual keying, just ask away =)

/Henrik

[Adrian van der Park]

Definitely use diffused lighting. I've been on a number of sets and they used banks of 5500 Kelvin fluorescents.

I use the GE Daylights (rated 5500K) in cheap housings, but use the best ballasts I can get my hands on (to stop that 60Hz hum and flicker). Work great for indoor shoots. If outside, try to pick an overcast day around noon.

Again as someone else mentioned, DV has the crappy compression. To get around it, you have to really whack everything with light so that you get good contrast ratio. The amount of cleanup and garbage matting will be higher than if you used film or dBeta, but use what you have to. (I wouldn't want to have to do 70 shots of green cleanup from dv footage). If possible make sure that the edges of your actors have good rim lighting so that you have a nice forgiving edge to eat into slightly if you must. Generally, the more contrast against the blue or green you have, the easier it will be to key. Long flowing or short spikey hair and see through materials should be minimized.

Also with more light, use ND filters and keep your iris open to get heavier DoF, and try to use longer zoom lengths. And yes, keep subjects as far away from screens to min the spill light. But most professional keying packages have excellent spill supressors.

Adrian van der Park
VFX technical director
Rainmaker Digital Pictures
Vancouver, BC

[Jacques Mersereau]

A lot of good advice on this forum.
IMO, you are going to have a hard time trying
to get a good key with a few quartz lights
(I'm assuming 500 watt work type lights).

Someone said:
"The goal is to get as even green / blue shade as possible and to avoid coloured light to spill onto the subject."

This depends. Some software programs like
Primatte in Commotion can actually use that
spilled (blue or green) light on the subject
to replace it with sampled light from the
background you are compositing onto, thereby
helping to blend the two together.

Now, if you aren't using Primatte, then you want
to back light your subject with another color that
will over come the spill (reflected green or blue).
One of the most commonly used gels is straw
(Lee-103).

What is really crazy is that each different kind of keyer has its own personality. Some work better
on DV than others. Gurus at this stuff use Primatte, Ultimatte, Keylight, and zMATTE.
I'm sure there are others. I know the first three
are good.

But, an evenly lit background is
the most important and hardest thing to achieve.
I have had best success with:
2 1000W softboxes for small stuff.
2 5K fresnels for large stuff.
This doesn't include lighting the subject, screen only.

It's not as easy as those demos you see at the
trade shows ;)

[Charles Papert]

In addition to the good tips represented here, it is pretty standard to add green gel to your lights that are illuminating the green screen (or blue gel if a blue screen is in use), to maximize the saturation of the key color.

[Dylan Couper]

Another tip would be to throw a back light/kicker light on your subject to highlight his/her form. This will reduce any glare from the blue/green screen that might be picked up on clothing. This is more important if you subject is very close to the screen. No a big deal if you can move further away from it.

[Rob Lohman]

Ed, could you e-mail me those two PDF's at visuar@iname.com
please? Those url's don't seem to work and I cannot find them
at 2-pop myself. Thanks.

[Adrian van der Park]

I don't know what you would find in those pdf's that isn't covered here.

Between all the tips posted here, this is pretty much what you need to know for shooting green/blue screen material with the intent to get a good key.

Adrian

[Ed Frazier]

Hi Rob, This thread was started just about a year ago and I guess that might explain why those links are no longer valid. I'm not sure, but I think these are the same two articles:

http://www.videouniversity.com/chroma1.htm

and

http://www.videouniversity.com/chroma2.htm

[Andre De Clercq]

Besides all optical precautions and some processing tricks, try to use (if you start from DV footage) an NLE system (Canopus Storm?) using interpolation. This gives you a 4:2:2 equivalent keying resolution.

[Rob Lohman]

Ed,

I just noticed that indeed. Heh. Not always too obvious. Thanks
for all the tips and such!

Cheers!