Radio-Television-Film - Equipment Tip Sheets

SHOOTING ON A "GREEN SCREEN"

This is a very short “cheat sheet” for you guys while you are shooting scenes to color key, courtesy of Geoff Marslett . Take it as a starting point. The best way to get better at shooting for color keying is to practice. There are a lot of conflicting ideas about the best way to do this. I will give you my recommended way to do it--but please try others if you do not like your results doing it my way.

There are a lot of good resources for this, see links at bottom of page. I encourage you to do a google search or follow some of my suggestions and read more about it. Also most effects books will give you great tips too.

If you try this…good luck.

One more note. DV is not a very good format to shoot color keys with. Beta, Digi-Beta, film and HI-Def are all better choices. Having said that, it CAN be done with DV, and I am going to assume that you will have access to DV. So here we go…

This information is in no way a substitute for paying attention in class!

Regardless of the lights you use, the color of the screen, or what the replacement scene will look like, ALWAYS LIGHT THE BACKGROUND AS EVENLY AS POSSIBLE. It will be far more important that the background is evenly lit than whether it is one stop over or under the key light. *

Pick a color for your background that is not present in your foreground and will therefore be easy to key out. Generally blue or green chroma key colors are used. I prefer fabric or painted walls over paper, but use what ya' got. If you have the resources a "digital" blue or green screen or the spongy “pro” backdrops are nice. *

Though some people will say, “Why light a big area if you only need to key a small thing?” I say, “Use as big a screen as you can and get your foreground as far away from the screen as you can.” I say that because it will keep spill and reflection on your foreground down and it might give you enough distance to make the green screen be out of focus. This hides imperfections in the material and lighting and gives you a smoother background to key out. And a little side note here, if your shot is too wide and you see some of the studio around the key--it will not be a problem so long as your foreground never crosses into the backgroundless part of the shot. You can use a garbage mask to clean up the shot before you key it. *

I recommend lighting the background about ½ to 1 stops under the foreground exposure. This helps saturate the color and by being less bright it helps keep the color from reflecting onto the foreground character. I recommend this for regular, well lit scenes in which the foreground being keyed is supposed to be “well lit”. If you need the foreground to look high contrast or dimly lit, I would advise having the background over-exposed. The idea here is to keep it different from the foreground. But all things being equal, a little under-exposure is my preference.

* Light your background first. Get it really really even. No shadows! No hotspots! I recommend using the light meter to do this. You can also use the zebra pattern on your DV camera to double check this. *

Next turn off the background lighting completely and light your foreground to match the scene it will be composited into. Try not to spill this light onto the background as it could mess up your nice consistent lighting on the green/blue screen. Use black wrap or barn doors or flags to block off this spill. *

Turn all the lights back on and re-meter. If you have spill problems or reflection problems, you can sometimes clean these up by backlighting your foreground. *

Double check any reflective, sharp, or metallic elements in your foreground to make sure they are not reflecting any of the green or blue screen. *

Here I am going to just insert some filter/gel info. Take it or leave it. A lot of folks recommend some version of this. To be honest, I haven't bothered to use the gels, but hey it might make the keys look better and with DV you probably need all the help you can get. “Lighting Gels: (for the screen) If you are using "digital" blue or green screen materials from Composite Components and the specified lighting from either Kino-Flo or Flo-Co, you probably don't need to augment your lighting with gels. On the other hand, if you are using the "Chroma" blue or green spongy material and lighting with Kino-Flos or Flo-Cos, you should probably add at least a full stop CTB (Color Temp Blue) for the Blue Screen and a Full Stop of Green Gel for the Green Screen. If you are lighting the "Chroma" Blue with tungsten light, then you should add a lot of blue such as Lee (119), Roscoe Cinegel Medium BLue (661 or 83) or Dura 60/70 and, in the process, you will need a lot of lights as well. *

Lighting Gels (for the Foreground): If you are concerned about the separating ability of the foreground with the blue/green screen, you can augment the separation by adding a slight amount of opposing color to the foreground or subject lighting. If you are lighting a green screen, a 1/4 or 1/2 stop minus green might help give better separation while augmentation of a subject in front of a blue screen could use a Y-1, Pale Yellow, Straw or 85 Daylight Conversion.” *

If you are using a software like Ultimatte, shoot a take without the foreground. In other words shoot the empty back drop.

Here are a few links to some online resources. I don't endorse or agree with all of what these sites have, but I am a firm believer that multiple opinions are often helpful. The blue screen page from StudioDepot.com has a good quick overview: http://www.seanet.com/Users/bradford/bluscrn.html

A do it yourself page from film-and-video.com: http://www.film-and-video.com/broadcastvideoexamples-greenscreen.html

A check list from VCE.com: http://www.vce.com/bluescreen.html

Some Tech Specs from Kinoflow: http://www.kinoflo.com/product/b_g_screen/bluegreenscreen.html

Some back and forth discussions on DV Creators.net: http://www.dvcreators.net/discuss/showthread.php?t=7197

Some more online discussions from Cinematography.net: http://www.cinematography.net/.../greenscreens_bluescreens.htm and http://www.cinematography.net/.../CML%20Blue%20Screen%20vs%20Green%20screen.htm