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Old August 23 2012, 10:19 PM   #215
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Re: Fan Filmmaker's Primer

New topic:

There are a few tricks about setting up a greenscreen that fan filmmakers should be aware of.

1. You want to keep the greenscreen as far away from the talent/objects in front of it because it:
  • prevents the latter from casting shadows on the green
  • helps minimize the chance of green "spill" onto them
  • allows you more latitude in positioning lights to hit only the former or latter
2. Take the time to minimize wrinkles and folds in the greenscreen. The smoother and flatter it is, the easier it is to get a clean matte.

3. Put tracking markers on the green even if you're not planning to move the camera. Two or three small X's of tape will do, placed where that the actors/props won't pass over, or done with green tape of a different shade. Easy to crop out, but handy to have if you decide you DO want to pan or tilt or dolly, as it will help keep the background aligned.

4. You want to try to light the screen so that it appears a relatively even green without hotspots or dark spots, because the amount of color information in the extremes is lower and ergo harder to key out.

5. While keying software typically lets you key out virtually any color, the reasons green is the most common keying color are:
  • on most digital video cameras the information in the green channel is typically the sharpest
  • there's very little green in most flesh tones
6. To minimize green spill on hair or other shiny parts of a costume, use a top or backlight with a MAGENTA gel on it. Magenta is the opposite color from green, and will tend to neutralize green reflections. Just make sure such lights are flagged so as not to hit the greenscreen. (You can easily eliminate any magenta tint on the actors in a color corrector, assuming you don't overdo it).

7. LOCK THE EXPOSURE. If you're using autoexposure (I recommend not), once you have the shot looking right switch the autoexposure OFF, otherwise the camera will keep adjusting the exposure because your actors are moving and this will make keying messier.

8. CHECK THE FOCUS. The mushier the focus, the harder a time you'll have getting a good matte. As with autoexposure, don't use autofocus.

9. Watch the shot on a monitor. Most small cameras screens are small enough where you might not notice if the focus is slightly soft, etc.

10. Don't worry about anything part of the greenscreen that nothing passes in front of. Cropping and garbage mattes are used to get rid of any parts of the frame where foreground objects don't cross.

11. SHOOT A CLEAN PLATE for every setup. Meaning, shoot the greenscreen without anything is front of it for a couple of seconds. Why? Some keying software has the option of allowing you to use a "clean" frame" as a reference, and it compares each frame of the shot to the clean frame to look for differences, sometimes making for sharper mattes because there's more info to work from.

* * *
Well, I've been to one world fair, a picnic, and a rodeo, and that's the stupidest thing I ever heard come over a set of earphones."
óMajor T. J. "King" Kong

Last edited by Maurice; August 24 2012 at 06:24 AM. Reason: corrected typos
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