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Old May 3rd, 2008, 07:06 AM   #1
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Green Screen Advice

Hi,

I took a phone call yesterday from a client enquiring about the possibility of me doing some green screen/chroma-key work. As usual I have to get the ball rolling pretty quickly (although I prefer it this way - it's the only way to learn!) and will set up a meeting some time next week.
I suggested I'd look into over the weekend and have set aside time to investigate the realms of this technique (having not promised anything but keen to give it a go).
I have a couple of browsers open from the Ken Stone website with a great deal of helpful tips and techniques, but would love to hear from you folks on here (where to be fair I've amassed most of my related knowledge from :) ).

There were a couple of posts on the JVC boards relating to this subject (which I've read through) but they are a couple of years old (and may have referred to older versions of FCP).
I'm running FCS1 (FCP5, motion et al) alongside the HD100.
I think the key here is budget (possibly on their part as well as my own)....which is as constricted as ever. The footage may end up as clips on websites (it's for a design company) rather than DVD, but until I meet I can't be sure.
I could probably extend to purchasing the cheapest possible muslin (a poster on here has used a roll of graphic paper with apparently decent effects); I'd thought of popping in to either a large, local camera store, ebay, or perhaps a fabric shop. There are a great deal of solutions out there (plug ins; AE etc) but I simply cannot go that route at the moment.

The DVcreators site has a few good tips about lighting (which again is on a budget...might be a case of hiring for a day and using the living room as the 'studio') with advice on a uniform zebra and lighting the subject from above producing a white rim around the subject. Ultimately it will come down to trial and error, but it might be a good opportunity if all goes ok.

Any suggestions would be greatly received.
Thanks.

ps: is there chromakey work on Tim's (soon to be PAL? :) ) tutorial DVD?
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Old May 3rd, 2008, 12:10 PM   #2
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I'm afraid I didn't get into green screen in the volume 1 ProHD DVD. The rules of lighting for green screen apply to all cameras, HD, SD or film, so we might do something for another 'Cinematography Tips DVD' idea we've been batting about.

Here is my #1 tip for green screen work: counteract spill with 'minus green' gels (magenta.) Spill suppression will work to a certain extent in post, but try to get rid of it all on set and you'll be a happy camper. The basic concept is that the opposite colour to green is magenta, so magenta will cancel it out.
To do this turn off your key and fill lights, leave the green screen illuminated, and then rim light/back light your subject with 'minus green' until you see no spill. This is especially important on subjects with blond hair or a bald head.

Here's an example I shot for a client last year. http://www.intervent.ca/programs/ Click on the "90 second educational video" to see the end result. This was shot at 720p30 with an HD100 and the 13x3.5mm lens. I easily composited and keyed everything within Apple Motion 3.

EDIT: Added a behind the scenes photo from that shoot so you can see how it was lit. The BG was lit flat mostly with a motorized Broncolor Cumulite on fill mode and the lower shadow areas filled in with a Rifa softbox. The subject was filled with a Diva Kino, a 150W tungsten Fresnel used for an eye light, keyed with another Rifa (which also spilled onto the green screen) and 150W Fresnels with minus green were used for rimming his head. I would have normally only used one, but the client wanted a second hotspot on the other side of his head for "symmetry." I wasn't totally happy with this but you have to do what the client wants sometimes.
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Green Screen Advice-intervent-green-screen-cropped.jpg  
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Old May 3rd, 2008, 12:56 PM   #3
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Tim's sugestion on magenta will work in most situations. I would presume thought that (in this case) a design company would be very particular about the light colors being used. Lighting a greenscreen is very subjective but there are a few "rules."

You probably already know this but the key (no pun intended) is to make sure that you don't light your greenscreen too much and that you light it evenly! We used to use cheap halogen worklights at a very high angle to the camera and that worked very well, most of the green spill hit the floor then. Also, keep your subject about 3 to 4 feet away (or more if necessary) from the greenscreen, that will also reduce the spill. Doing this made it so we didn't have to do very much (if any) color correction in post.

For a fill I usually used a bounce or kept the key very high and the fill low to eliminate shadows on the greenscreen.
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Old May 3rd, 2008, 01:24 PM   #4
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One more tip:

If there is any motion shoot above 1/48th of a second shutter. 1/100th will help minimize motion blur that will just cause you headaches later. You can artificially add motion blur back in after the key is cut.
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Old May 3rd, 2008, 08:41 PM   #5
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WOW, I agree with you that the double hot spot looks really strange. Even if it is "symmetric"
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Old May 4th, 2008, 04:10 AM   #6
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Thanks everyone - I feel much better about this now (almost to the point where I may perhaps pull this off!).

Quote:
Here's an example I shot for a client last year. http://www.intervent.ca/programs/ Click on the "90 second educational video" to see the end result. This was shot at 720p30 with an HD100 and the 13x3.5mm lens. I easily composited and keyed everything within Apple Motion 3.
This would be perfect and probably what they're after (it won't at all be corporate...maybe even a vanity project/s for some of the key staff - simply people talking in front of the camera, nothing too acrobatic). I couldn't hope to get it spot (again no pun intended!) on like that but I'll try my best with the kit I currently have. Good tip re the Magenta gel and luckily I know of a local firm who supply a range of gels.

Quote:
You probably already know this but the key (no pun intended) is to make sure that you don't light your greenscreen too much and that you light it evenly! We used to use cheap halogen worklights at a very high angle to the camera and that worked very well, most of the green spill hit the floor then.
I knew hardly anything about green screening before these posts (and a few reads on the internet) Doug, so again thanks for all of the advice.
Interesting to read you used halogens - because here's my [current] plan:

The client mentioned he wanted a quick test to show the team (he's the head of design and they are the folks requesting this project) but suggested I could merely test against my hand (as an example) over a bit of green/blue cloth - now I can imagine this would look 'bobbins', so I'd like to step this up a few gears as much as my budget allows.
Unfortunately I do not currently own any lights (believe me they're up there on my priority list) but would be willing to hire some in. I'll use my living room as a 'studio' and the use of halogens is interesting because directly above the backdrop are halogens - if I could use these to some effect then that would be extremely handy.
Again due to lack of budget, rather than purchasing a ready made frame for the green material I'll nip to the local hardware store and grab some ply in order to construct a (dismountable) frame. I have a ringlet device I can use to hold material taut if need be. Is there any type of suitable material I might be able to use which is pretty much 'green screenable'?
Tempting to look at some of the more costly solutions (the chromatte system with the led rings and glass embedded screen!) but absolutely not an option.

I can position the subject 3/4 feet in front of the screen but the due to the small size of the room the camera lens would have to be fully zoomed out (the camera will be also backed up against the back wall).
I'll shoot in 720p25 (over interlaced) as I'm fairly certain they'll be impressed with the progressive look of this camera.
I've read that you should have the zebra eliminated (a uniform zebra from a 'non hotspot' lit background) via one or two steps down (set zebra at 100%?) then when the subject is positioned then drop the aperture down a further couple of steps (drop from 2 to 4 as an example?).
Might there be any preferred scene files for this type of shoot?

Aside from not using transparent objects in the shot, green (or blue) clothing and over excessive movement, I'm good to go - the lighting is the most worrying part for me.

Quote:
One more tip:

If there is any motion shoot above 1/48th of a second shutter. 1/100th will help minimize motion blur that will just cause you headaches later. You can artificially add motion blur back in after the key is cut.
I was aiming to shoot 1/50 (as I usually do with 720p25) - interesting mention of artificially adding motion blur - would this be for technical reasons or aesthetic (more filmic look?).

I'm sure I'll have a few questions come post production - I was intending to use FCP (5) rather than motion (v2) - I presumed FCP was the only way to go (if you only had the FCP suite at your disposal)?

Huge thanks for your time answering my questions.
Cheers all.

EDIT:
*This attachment shows where I intend to build the backdrop (directly in front of the brick fireplace/tv panel).*
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Green Screen Advice-tv-front-view.jpg  
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Old May 4th, 2008, 05:11 AM   #7
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Though I was never the guy responsible for lighting, I've been on a lot of greenscreen shoots--always in a controlled studio environment. #1 problem was always spill. We had a cyclorama and full body shots presented even more problems with spill.

The other thing is know your background before lighting the subject. Indoors? Outdoors? Which side it the key light?

Another useful tip would be to avoid using your fireplace for burning wood!
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Old May 4th, 2008, 05:32 AM   #8
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Quote:
Originally Posted by Brian Luce View Post
Though I was never the guy responsible for lighting, I've been on a lot of greenscreen shoots--always in a controlled studio environment. #1 problem was always spill. We had a cyclorama and full body shots presented even more problems with spill.

The other thing is know your background before lighting the subject. Indoors? Outdoors? Which side it the key light?

Another useful tip would be to avoid using your fireplace for burning wood!
I presumed most of the shots will be indoors but outdoors would be handy (using the sun as a good lighting source). Trouble is, in the UK the indoors environment is your friend :)
Has anybody shot green screen outdoors?
I think I'm most worried about green spill - if it's not done well it end's up looking like a dogs dinner.

Yup - there's enough electrics within the fireplace to heat the room off it's own back!

Just spotted this material on ebay (seems like a good price too):

http://cgi.ebay.co.uk/TUFF-PHOTOGRAP...2em118Q2el1247

Cheers.
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Old May 4th, 2008, 07:18 AM   #9
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An excellent chromakey solution...

Hi David

I am recently in a similar situation. My client wanted 17 interviews shot against a greenscreen, all to be shot within one day in Birmingham (while I am based in Brighton!). Time and distance meant I wouldn't have much time to set up an elaborate lighting system in their board room. Here was my solution.

I hired the Datavideo Chromakey, which is a dual colour LED ring with a retro-reflective backdrop cloth -this system does not require you to light the backdrop, you only need to light the subject, plus it gives up a perfect key in either blue or green depending on what the subject is wearing. You can see the system I hired here: http://www.hireacamera.com/camcorders/clk100.asp

Some considerations: you need a 82mm-72mm stepdown ring for use with JVC HD cameras. Also, I am presently exploring the use of the After Effects plugin 'Keylight', apparantly used on Harry Potter and other big budget films -you can download a 'rented' version of it that lasts for one day, for only
1.75 (!) at http://www.thefoundry.co.uk as I have found most of the standard chromakey presets in NLEs are not good enough.

I have a May 10 deadline so will let you know how I get on.

Regards
Dan
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Old May 4th, 2008, 09:01 AM   #10
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Cheers Dan - aye, I've seen that set up (Chromatte I think - developed by an ex BBC guy). I think there are a few dissenters mind but I couldn't tell you what their niggle with them was. Definitely a consideration however (I'll look into the step down rings, might need these for other lenses also) and perfect for you cross county trip :)
Unfortunately I don't have AE (add that to my wish list!) so I'll have to see how I get on with either FCP or motion.
Let us know how you get on with it Dan.
Cheers.
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Old May 4th, 2008, 11:17 AM   #11
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Quote:
Originally Posted by Dan Parkes View Post
I hired the Datavideo Chromakey, which is a dual colour LED ring with a retro-reflective backdrop cloth -this system does not require you to light the backdrop, you only need to light the subject, plus it gives up a perfect key in either blue or green depending on what the subject is wearing.
This is totally alien to me; lighting the talent and backdrop from the camera. I can't see that being a good idea. Also I doubt you get an evenly lit bg. But I'd be interested to know how this works out.

My 'rules' for ck-ing are:
- Light backdrop evenly with soft light, don't overexpose
- Get some distance between talent and backdrop, >> 3 ft.
- Light the talent as required (usually 3 point system)
- Flag lights to prevent spils

You can use green filters on the lights lighting the greenscreen; I've used Lee 138's for this with good results. The Lee 738 is supposed to be even better, but haven't tried it myself.

Depending on how you're shooting the talent, it can get more difficult. Wide shots or dancing is (much) more challenging than talking heads or fairly static medium shots.

Best go somewhere you have some room to work with. Your living room may not be the best choice. Having more room will enable you to control spill by moving the talent further from the backdrop and to choose the best camera position.

Having a good CK-pluging or app. make the work that much easier. I use Primatte Keyer (Red Giant Software) but I've also heard good things about dvMatte (dvgarage.com). Both of these are much better in spill removal then the standard keyer in FCP.

George/
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Old May 4th, 2008, 11:25 AM   #12
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Quote:
Best go somewhere you have some room to work with. Your living room may not be the best choice. Having more room will enable you to control spill by moving the talent further from the backdrop and to choose the best camera position.
Thanks George: I'll discuss this with the client next week - perhaps I could use their offices. The initial phase is for me to show some test green screen footage hence the living room. If that comes off *ok* then I guess there's room for me to develop this further.
Is spill really that obvious when you're filming (bearing in mind I've never been on any type of chromakey shoot)?

I think I might initially purchase the muslin green screen cloth I saw on ebay earlier (linkie posted) - for 28 (and apparently pantone colour matched) it's a start for test footage at least - but really it's the lighting I'm more concerned about.
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Old May 5th, 2008, 06:15 AM   #13
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Originally Posted by George Kroonder View Post
This is totally alien to me; lighting the talent and backdrop from the camera. I can't see that being a good idea. Also I doubt you get an evenly lit bg. But I'd be interested to know how this works out.
George/
Sorry George, I think you misunderstand the process. The LED ring does not light the subject at all. It only creates either a solid blue or green background behind the subject, allowing you to focus entirely on lighting just the subject using the usual 3-point system or whatever is required. The clear advantages here of using reflective media as a BG is that even if the BG has creases or crinkles it will not affect it and you can instantly change the BG from green/blue depending on the subject's clothing, plus it saves a lot on setup time.

This technology has been used by many broadcast TV stations for the weather segments for years but is now just becoming available for others. As soon as the system was advertised here in the UK it was instantly sold out and is presently on back order, so I have only been able to hire it.
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Old May 5th, 2008, 10:45 AM   #14
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Quote:
Originally Posted by Dan Parkes View Post
This technology has been used by many broadcast TV stations for the weather segments for years but is now just becoming available for others. As soon as the system was advertised here in the UK it was instantly sold out and is presently on back order, so I have only been able to hire it.
I've read reviews of these pricey rigs and was left with the impression they solve many issues with chromakeying but also create new a lot new problems.
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Old May 5th, 2008, 11:58 AM   #15
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Originally Posted by Dan Parkes View Post
Sorry George, I think you misunderstand the process. The LED ring does not light the subject at all. It only creates either a solid blue or green background behind the subject
Hi Dan,

First I heard of this so forgive my ignorance, but how do you prevent the LED ringlight from lighting the subject as well? It's right there on the lens (as seen on the link you provided).

Sure, the keylight will be much brighter than the LED's, but doesn't this create problems in the shadows?

Quote:
This technology has been used by many broadcast TV stations for the weather segments for years but is now just becoming available for others. As soon as the system was advertised here in the UK it was instantly sold out and is presently on back order, so I have only been able to hire it.
So good results? What kinds of shots/setups? Can you post screengrabs (LED on/LED off if possible)?

George/

P.S. I'm veering off topic a bit, maybe this calls for a new "Experiences with Datavideo CLK100 Chromakey solution" in Open DV or Photon Management forums?
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