I will use the term "greenscreening" predominantly in these rules, rather than chromakeying. Obviously, you can substitute blue if you choose to shoot with bluescreen. Or, any other color you may choose to shoot with, for that matter.
Rules to Shoot By
Make sure that your background is opaque and without wrinkles. While this can be a permanent enclosure in a permanent greenscreen studio, it can also be a temporary setup. We’ve included an article on making a great greenscreen backdrop that’s opaque and wrinkle free for about $50 in this issue, which you can read here. (Plus, it includes a good paint color choice you can pick up at Lowe’s or Home Depot.)
Keep at least 6’ between your actor and the greenscreen and 6’ between the camera and the actor. This prevents shadows from hitting the background and lowers the amount of “spill”—reflected green that washes over your actor.
Use soft boxes or some sort of diffuse light to light your greenscreen. We’ve used the twin 500W Smith Victor Economy softboxes that make up their KSB-1000 to good result. With a little creativity and some heat-proof diffusion, you can also use three 500W 3200K flood bulbs in three Home Depot clamp scoops (the ones that have porcelain fittings) for about $40 for all three. (However, you really have to pay attention to rule #4 if you do this.)
Use a light meter to test that you have even lighting across the background and make sure you have no more than a 10% variance in illumination in any part that will be filmed. While you can use a handheld light meter, my recommendation is that you plug your camera into a laptop that has some sort of lightmeter software in it. Adobe’s OnLocation CS3 (which was Serious Magic’s DVRack 2) is an excellent example of this. (Also, if you have a software package like Adobe Ultra CS3, you can actually do test keys to see how well you’ve lit things. Folks who buy the PC version of Adobe’s CS3: Production Premium will have both of these helpful packages included in the bundle.) [If you don't have a lightmeter or a laptop with the necessary software, you can make a cheap lightmeter by adjusting the two zebra levels on your camcorder and zooming in on different parts of your screen with the auto-iris turned on. If you adjust the zebra levels close enough to one another, you'll be able to make sure that you're within a 10% illumination variance throughout your screen.]
Don’t overlight your greenscreen. You want the background to be as close to pure green as possible. If you overlight the background, you will wash out the green color and you will have difficulty keying the background properly. Additionally, there is a greater chance that green light will spill on your subject if the screen is overlit.
Light your main actors dynamically and with separate lighting than your greenscreen. The lighting is designed to look like the lighting in the background you will be adding in post, and is usually three-point light—which is made of a key light, a fill light, and a kicker. (This is another great thing about having a laptop with you, as you can see the background image as you are setting up the lighting. Plus, even if you don’t have Ultra, you can record a few seconds of footage, digitize it real quickly, composite it in your favorite keyer, and make sure your lighting will blend with the background.) The most realistic keys match this perfectly. (Just make sure that you spread your key and fill lights a bit wider than normal to prevent their light getting on the greenscreen, or you could screw up #4, #5, or both.)
Turn off all the lights which are illuminating the greenscreen before white balancing. This is a very helpful fact that Tom Stern brought up in his MFM article on shooting DVX/HVX greenscreen footage. As this tip applies to all greenscreen shoots, I repeat it here. If you white balance with the greenscreen illuminated, it screws up your white balance and basically causes the green to become washed out. (Which basically leads you back to issue #5) Just don’t forget to turn back on the greenscreen lights before you shoot your sequences!
Experiment with the camera until you get the settings that yield the most difference between your actor and the green background. Each camera is different, but the more true green you can record the background in your camera, the easier it will be. (If you have the DVX100 or HVX200, check out the aforementioned article by Tom Stern on its presets for greenscreen.)
If you have a camera that shoots progressive footage, shoot progressive. Interlacing makes it harder to get a clean key, and will therefore have to be removed in post, anyway.
If you have a camera that shoots 24 fps, shoot with that. Cameras that shoot true 24 fps usually have their shutter open 20% longer per frame, which means that more light data is being recorded. As many of the keyers designed for DV/HDV/HD footage combine luma and chroma data, the more data you can record on both levels, the better the key they can produce.
If you can shoot at a higher resolution than what your project demands, do so. Obviously, the greater the resolution your camera can record, the more data for the keyer to work with afterwards. The huge benefit in shooting at a higher resolution than what you will output at is that you can key at the higher resolution and then shrink the image to fit the output resolution. This will give you much more precision and make minor keying artifacts virtually unnoticeable.
Don't shoot greenscreen with a 35mm adapter. If you've read any of the articles, critiques, or reviews in this magazine, you're probably aware that we love the film look a 35mm adapter can provide. However, for greenscreen work, you want your subject to have sharp, clean, in-focus edges. Once you've keyed your subject cleanly, then you can create the look of shallow depth of field in post with out of focus backgrounds and feathered focus edges on your subject.
While these are the main rules to shoot by, I wouldn’t be very helpful if I didn’t also leave you with some information about what to watch out for with your talent. You can do all these twelve things perfectly, and talent can cause problems if you’re not careful.
Don’t have your talent show up until you have most of the greenscreen set up. Unless you have built a greenscreen studio and will be shooting in there, then you should plan on at least two to four hours to set up a greenscreen and light it properly for the first time. You don’t want your talent hanging around getting bored, tired, and cranky. (And you don’t want them to get hot and sweaty, as we cover in #4.)
Make sure that your talent wears nothing green--or that is largely green derivative. There are lots of things like teal and aqua that are a perfect blend of blue and green which are bad choices for your talent to wear, but which many people wouldn’t realize because they get tunnel vision on avoiding just green.
Make sure you have nothing shiny on your actors or as part of the physical set. Shiny things reflect green and therefore will become transparent. Matte clothes are best for actors and matte finishes on pieces of furniture you may use. As even glossy wood furniture can reflect green, you can imagine what happens with stainless steel furniture and glass table tops. Same thing goes for props like water bottles, crystal balls, and reading glasses.
Make sure you have fresh make up on your actors at all times. While makeup is necessary for any film endeavor to get the look you want, it’s extremely important for greenscreen as it prevents your actors from becoming shiny and reflecting greenscreen light. With your actor(s) standing in front of one set of lights and right near another bank of lights, you can be sure that the makeup will melt off at a faster rate than in other types of shoots. As such, plan on having the makeup refreshed regularly.
Hopefully this has proved helpful to you and will allow you to explore the amazing world of chromakey technology! For more information on chromakey and greenscreen technology, check out the rest of the articles in this issue and watch for future issues in which we deal with more advanced applications of these topics.
The
director of two feature length films and half a dozen short films,
Jeremy Hanke
founded Microfilmmaker Magazine to help all no-budget filmmakers make
better films. His first book on low-budget special effects techniques, GreenScreen Made Easy, (which he co-wrote with Michele Yamazaki) was released by MWP to very favorable reviews. He's curently working on the sci-fi film franchise, World of Depleted through Depleted: Day 419 and the feature film, Depleted.
