Greenscreening Windows

David Jimerson

David Jimerson

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Staff member
Thinking about this for my upcoming shoot . . .

I'm going to shooting in daytime in a house with some pretty large windows. I expect the light spill to be very bright.

I was thinking of blocking the light and going entirely artificial by greenscreening the windows.

I've thought about making it somewhat translucent so that the outside light makes it bright for keying purposes (and would theoretically be fairly even), but I'm worried about green spill.

I've thought about making the greenscreening opaque, blocking out all outside light, but then there's the problem of lighting the green.

Maybe it isn't such a good idea, but if I could make it work, it would solve a few problems . . . like setting the house in a completely different neighborhood.
 
Re: Greenscreening Windows

Simplest thing would be just to ND (and color balance as needed) the windows if you don't need to replace the exterior. This is standard practice for video and film.

If you're not moving the camera all over or having a lot of action in front of the window then you could consider rotoscoping the window. Especially easy if you're locked off.

If you are going to greenscreen you have to consider your background images you will be using. Ideally shoot these first with same angle for your windows. If your camera is moving or the lighting is different (e.g front lit bg versus backlit fg) you're going to have a heck of a time.

You could go with translucent material and let the sky backlight but then you have very little control of the actual brightness to balance the fg.
You're going to have to cheat light as if it is coming from the window or go with translucent backing. Unfortunately you may find a lot more greenspill with translucent greenscreen windows.

My suggestion would be to avoid the greenscreen unless you _really_ need to replace the background. Rigging and lighting the green is going to take more time than filtering the windows to begin with and will more likely look better than trying to key and replace the Bg.
 
Re: Greenscreening Windows

Rotoscoping won't solve the light problem . . . and I've come to all the same conclusions . . .

Thanks for the input . . .

But I'm still trying to come up with a way to make it work! 8)
 
Re: Greenscreening Windows

[quote author=David Jimerson link=board=news;num=1089931270;start=0#2 date=07/15/04 at 16:50:41]Rotoscoping won't solve the light problem . . . and I've come to all the same conclusions . . .

Thanks for the input . . .

But I'm still trying to come up with a way to make it work!  8)[/quote]

Try out Combustion, it allows difference keying that is very high quality.
 
Re: Greenscreening Windows

[quote author=Slapdragon link=board=news;num=1089931270;start=0#3 date=07/15/04 at 17:07:09]

Try out Combustion, it allows difference keying that is very high quality.[/quote]

Tell me more about this Combustion! :o
 
Re: Greenscreening Windows

[quote author=NoMaD link=board=news;num=1089931270;start=0#4 date=07/15/04 at 18:06:04]

Tell me more about this Combustion!  :o[/quote]

Combustion brings Discreet's high end but expensive compositing, paint box, morphing, and animation tools to standard computers for the same price as a copy of Final Cut Pro, and with a program bu Automatic Duck, it allows round trip movement to and from editors. Basically, Combustion is a very powerful software based render engine for special effects. It can take, for example, Maya composites in 3D and run them into a video time line. It can composite video sources with very high accuracy (think star wars quality) and it has excellent paint tools for frame by frame painting. And if you come from Flame or Smoke, it is not too different in UI from those worthies. I love After Effects, but consider Combustion easier to learn.
 
Re: Greenscreening Windows

Rotoscoping- the point of rotoscoping is not to darken the windows but to make a simpler process of setup on the location (just ND down windows to match bg plate) and a simpler matting process. I do this for a living and I still suggest keeping it simple if possible.

Yes you can setup a greenscreen in the windows and key it but is it going to look real when completed and does it accomplish what you need? You can use any number of keying software packages.

In any case you still have to tone down the windows so it doesn't blow out. You could actually do a lumikey just by placing sheets over the window if you light your fg correctly.
 
Re: Greenscreening Windows

I think green spill is the least of your worries. Decent compositing software has such nice spill cleanup utilities that you could whisk it away in a matter of seconds.

The biggest problem seems to be (aside from pulling a clean matte w/o DV-jaggies) getting a good background plate that will match. And then match-moving that to the foreground (assuming the camera isn't locked down).. They make translucent greenscreen fabric such as....

http://www.bhphotovideo.com/bnh/controller/home?O=WishList.jsp&A=details&Q=&sku=302984&is=REG

...that sort of thing MIGHT give what you want. As far as the natural outdoor light pleasantly backlighting the window greenscreens for even lighting that will be easy to pull a key on. But then you have all the headache associated with natural lighting... i.e. a cloud passes by and all-of-a-sudden your greenscreens are all lit wrong. Then you could get really ridiculous and actually set-up lights, outside, pointed at the windows to provide a constant light on the greenscreens no matter what the sun may bring.But that, combined with a tricky match-moved key on DV footage.... and *whew*.

You'd be better NDing the windows and then printing one of those HUGE fake cityscapes to hang outside the window. What do they call those? :P
 
Re: Greenscreening Windows

Hey David. You want to change the world outside the house? is it ugly? not fitting for the film? this sounds like a pain in the ass to do with greenscreen and dv. how many shots do you have? are they moving much? if you have a small number of shots, with not too much going on with the camera, i say block the windows out with black, or whatever. light your house interior the way you like. then do some roto work to cut the windows out and put your new bg's in. or just go au natural and let light be light and not block out the windows at all. you can still roto out the windows, and replace the bg this way too.

how close were you going to have the greenscreen to the house? if you put the GS right up to the window, your going to get some hideous spill. and will make a difficult job of keying gs dv even harder, that combined with the changing sun and clouds. generly, you want to keep gs around 15-20 feet away from your set or subject, for the least amount of spill, that makes for a giant gs, and alot of lights.

Scottdvx100, are saying to shoot the background images first? the images he will put behind the windows?

hemophilia, the cityscape backgrounds they print out are called backdrops, backings, or translights.
 
Re: Greenscreening Windows

If you are going to key out the windows and replace them with another background you have the choice of shooting bg plates before or after your foreground (fg).
Before advantages: You now have lighting to match the fg to and may be able to check your comp on the set depending on setup. This is usually done if most of the frame is the BG.

After advantages: Freedom of angles when shooting the actors.
Measure the tilt on the camera (which you'd have to do above as well) and match it when shooting the bg. Unfortunately you'll have to check sun angles to get somethign similar to how you lit your fg. (Very dependent on how much of a role the window light is)

If you're moving the camera it makes it much tougher. If it's on a tripod at least try to mount the lens close to nodal. (pan/tilt center) You might be able to get away with 2D motion trackign if it's not too big of move.
 
Re: Greenscreening Windows

i think the norm is to shoot the foreground plates first then match the angles on another location for your backgrounds. i think your action plates should dictate where your camera goes, not the other way around.
 
Re: Greenscreening Windows

Man, I really shouldn't have tossed in that throwaway line about changing the scenery outside the windows . . . that's the least of my concerns, really; just an afterthought. Was never seriously going to attempt it . . . ::)

I do appreciate the great discussion, though!

I'm prob'ly just going to gel the lights and ND grad the cam.
 
Re: Greenscreening Windows

FG vs BG plate order is all based on the shot. If you have to matte someone into a scene then you need the scene to tell you where to place him in perspective (i.e. person walking down steps of a building)
If the BG is outside then you also have the issue of matching lighting, hard to do if you've shot a stage shot and now need the outdoors to match.
If you can control the bg (miniatures or CG) placement and lighting then you can do it second or if the BG will only occupy a small area then you you can last.
 
Re: Greenscreening Windows

yeah i understand "FG vs BG plate order is all based on the shot". i was refering to davids particular setup, i wasnt making a blanket statement for all shots all the time.

shoot a lighting reference rather then shoot bg plates if your worried about not having light match. there still is no a need to lock your self up because of the bg plates you shot. you shouldnt have a hard time lighting a scene say anytime of the day, then after the shoot go off and do your bg's. you can still color correct in the composite should the lighting be off, which happins alot anyway. just because you arent doing miniatures or cg doesnt mean you have no control over natural lighting. all you have to do is wait for the right time of day and point the camera in whatever direction it needs to be to get the shadows right and your good.

anyway, just my personal preference.

peace
 
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