To the moon, Brian!
WHAT YOU NEED
> Pencil and paper for sketching your screen and noting dimensions
> PVC pipe (around $20, local hardware store)
> Green fabric, preferably polyester (around $5 at a fabric or craft store)
> Permanent marker
> Hacksaw
> At least 12 inches of adhesive-backed Velcro (around $10)
> Digital video camera
> Final Cut Express ($299, www.apple.com) or Final Cut Pro (part of Final Cut Studio 2, $1,299)
If you watch television news, you’ve seen the weather person standing in front of a giant map of your city, displaying the current temperatures and conditions. Of course, there isn’t a huge map plastered behind the meteorologist - he or she is standing in front of a green screen. This solid green (or sometimes blue) surface acts as a blank canvas that can be digitally replaced with whatever a video technician wants, from weather maps to sci-fi battle scenes. Green screens are used in television and film all the time (think The Matrix and 300). With just a few lengths of PVC pipe, some green cloth, and a touch of elbow grease, you too can place a subject into a different setting.
1. Plan Your Screen Size
Decide on what size you’re going to make your green screen. Plan on a small screen (3 feet by 2 feet) if you’re going to work with small objects, and a large one (8 feet by 7 feet) to work with people. We built a medium-size screen (5 feet by 3.3 feet) to allow us to shoot the upper half of a person or two.
Keep in mind that you’re going to place the screen at least a couple of feet behind the objects or people you’re shooting, so compensate by making your screen at least 20 percent larger than your subject area. Our screen structure is 6 feet, 8 inches tall with a 60-by-40-inch green area, just enough to provide a green background behind a standing person’s torso. To bring the screen to the desired height, we planned 40-inch legs and supports to make it tall and steady. In all, we needed two 60-inch lengths of PVC, four 40-inch lengths, four 24-inch pipes for the legs, and connectors to bring them all together. Sketch out your planned screen on a sheet of paper so that you can get the exact materials you need.
Plan your screen with a rough sketch that includes dimensions and also notes pipe connector locations and types.
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PVC piping, usually used for plumbing, will act as the skeleton of your green screen. The thickness of the pipes will depend on how tall or large you want your screen to be. For our 6-foot-8-inch screen, 1-inch diameter PVC pipe was sturdy enough to keep it standing up straight. To determine the thickness of PVC you should use, test out long pieces of different diameters of piping in the store, making sure it doesn’t wobble excessively at the length you’ve chosen.
Check the measurements on your schematic drawing to determine the lengths of PVC pipe you’ll need. Hardware stores generally stock PVC piping in very long lengths. Try to get long enough pipes so you won’t have to attach two pipes together to complete your structure - this will weaken the frame. Wherever you join two pieces of PVC, you’ll need a connector. You should end up with two 90-degree elbows for the upper corners and four T-shaped connectors (with three connections): two for the space between the side of the screen, the bottom of the screen, and the legs, and two for the bottom of the legs, for the supports.
Next, you’ll need the green fabric. We recommend material with a high amount of polyester, which is less wrinkle-prone than cotton. Measure the amount you’ll need based on the size of the green area of your screen, and add at least two inches to each side - our screen is 60 by 40 inches, so our fabric is 64 by 44. (If you’ve never bought fabric, note that it’s sold by the yard in the United States, but you can often purchase amounts as small as 1/8 of a yard. Fabric width varies too. Standard width is 45 inches, but this varies, so be sure to check.)
Take it from us: Don't start building until you know you have all the right materials.
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Measure out on the pipes the lengths you need and mark where to cut with a permanent marker. With a hacksaw, cut your PVC to the lengths listed on your schematic. Connect your trimmed pipes with the connectors to create the screen and the legs (use the two L-shaped connectors on the top corners, and two T-connectors for each side of the bottom of the green area), and then attach the four leg supports to the legs with the two remaining T-connectors.
Now that your frame is complete, lay out your green cloth, which should be a bit larger than your frame’s green area, and attach one side of six 2-inch strips of Velcro to it - three on the top and three on the bottom. If your fabric is wrinkled or creased, toss it in the dryer for a bit, or iron it on a low enough setting so as to not burn it. Then take the other side of the Velcro strips and attach them directly to the PVC, equally spaced on the top and bottom of the green area of your frame. Attach the fabric to the frame, and tighten by rotating the top and bottom pipes away from the middle.
Saw away from yourself, and use a clamp to steady the pipe, if possible. (Your body weight works too.) Safety goggles might be nice too.
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The set construction portion of this project is complete. Now to put it to good use: filming with it. Before you start shooting, some notes on lighting your screen correctly. Try to light your green screen as evenly as possible - consistency in the green color will make for a better end result. Also make sure your actors aren’t wearing any green, as those areas will disappear after you’ve removed all of the green when you edit the footage.
Before you shoot, consider what you’ll be replacing the green background with and do your best to match those lighting conditions. For example, light your subject from the right if you plan to add in a background from a late summer’s day with the sun shining from the right. Place your subject a couple of feet in front of the screen and begin filming. Because motion tracking with a green screen is extremely involved (and explaining how to do it requires a separate article), start with stationary shots in front of the screen. Don’t pan or zoom while you shoot, or your subjects will appear to float around and shrink and grow. But if that’s the effect you’re trying to accomplish, don’t let us stop you!
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5. It's Not Easy Being Green
After capturing and importing your footage into Final Cut Express or Final Cut Pro, trim and place your clips in the correct order in the Timeline - but instead of placing them in the V1/A1A2 layer, drag them a bit higher and place them in the V2/A3A4 layer. You need that first layer for your added background.
Find the clips you captured using your green screen, select them, go to the Effects window, and open up Video Filters. Find the Blue And Green Screen effect in the Key folder, and drag it onto the video clips that you shot in front of the screen. Most likely, the default settings won’t be exact enough and will require tweaking. In the Timeline, double-click the clips you dragged the effect onto, and in the Viewer window, set your Key Mode to Green. Now adjust the Color Level and Tolerance to better match the color green you used. Adjust the Feather option accordingly to make sure green lines don’t appear on the edges of your subjects.
Once all of your green screen clips show your subjects perfectly isolated over a black background, you can move on to the next step.
Removing your background can be tricky, but with a bit of tweaking and elbow grease, you can perfect it.
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Now comes the fun part: placing your subject in a different locale. Having picked your source image or footage to use in the backdrop, drag it into Final Cut to import it into the Browser window. From there, drag the background clip or image into the Timeline in the first layer (the V1/A1A2 layer) and drag the edges of the footage to fit the size of your green-screened clip.
To tweak the size and location of your background to make sure it fills the screen, double-click the background in the Timeline and set the Scale and Origin accordingly. With your background in place, try playing back your footage to see how the subject looks on the background. If you’re using Final Cut Pro, you can drag the 3-Way Color Corrector from the Video Filters onto either your source footage or the background, and adjust accordingly to match the footage, making them blend more smoothly.
With a different background, it's easy to create an action scene.
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After all this work, you probably want to share the video with friends. To put your video on a DVD, select all of your footage, go to File > Export > QuickTime Movie, and use the default settings for exporting. Once that has completed, launch iDVD (or DVD Studio Pro for users of Final Cut Studio), and import the QuickTime file by selecting File > Import > Video. In iDVD, choose a menu template, insert your footage, and burn.
If you want to share your creation over the Internet, in Final Cut, go to File > Export > Using QuickTime Conversion. From there, we recommend using the QuickTime Movie format; set the Use option to whatever medium you’re planning to stream your video over. If your destination is YouTube, for example, you’re going to want to use the DivX format, which can only be used after downloading the free DivX drivers.
Share your creation the old-fashioned way, on DVD, or the new-fashioned way, on YouTube.
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Links:
[1] http://www.divx.com/divx/mac
[2] http://www.maclife.com/article/apple_final_cut_studio_2
[3] http://www.maclife.com/article/final_cut_express_hd_3_5
[4] http://www.maclife.com/article/adobe_premiere_pro_cs3
[5] http://www.maclife.com/greenscreen
[6] http://www.maclife.com/article/advanced_green_screen_editing