UPLOAD
D
E
GREEN SCREEN TIPS. Fig. D: The subject has been
filmed against a greenscreen. A mistake made here
is the use of glass. As you can see, the green shows
through. Avoid mistakes like this.
For about $12 you can buy a 4-foot fixture containing
2 tubes. Depending on the size of your greenscreen
you may need 3 or 4 of these fixtures. I use sticks
and lots of duct tape to anchor them. You can then
light your subject with a couple of workshop clip
lamps using bulbs rated from 100 to 500 watts.
Remember that they must not cast shadows on
your screen.
3. KEYING
YOUR VIDEO
Now, let’s say you’ve shot your footage and you’re
ready to key out the green. On a Mac, you can use
iMovie with a plugin called Stupendous Software
Masks & Compositing, which costs $25. If you have
Windows, you can find free software such as ZS4
(
zs4.net/downloads), or economical all-purpose
editing software (with greenscreen feature included)
such as Video Edit Magic, available for free in a trial
version or for $69 fully featured, from trusted sites
such as
makezine.com/go/tucows.
3a. In iMovie, first import the video that you shot
against a green background, and place it in the
timeline. Then import the footage that will replace
the background, and place it next to your video.
Select the first clip, go to the Effects category,
and choose Green Screen, Smooth. This effect has
3 controls: Outside Fill, Inside Fill, and Choke. Play
around with these settings. The little preview window
will show a black and white sample. The 2 fill settings
determine how crisp the outline will be. You basically
want your subject to appear all white and the green
area to appear solid black; avoid shades of gray.
60 Make: Volume 12
Fig. E: Subject after the green has been keyed out
and new video inserted. The problem with the glass
is evident. Other issues show up too, such as the
green bounce light hitting the side of the chair. Color
correction can help to remove or limit the green.
The choke allows you to bite into the cutout to
remove jagged edges. Once you think you have the
settings right, click the Apply button. It will take
several minutes or longer to render your shot. Once
it’s done, you can watch your clip. You may need to
go back and change the settings a few times to get
the best results.
3b. In Video Edit Magic, place your background
video in the Video 1 timeline. Place your foreground
video (with greenscreen) in the Video 2 timeline.
Click the Video Transitions tab in the Collection
window and drag Chroma Key Color to the Transition
timeline. In the window that pops up, you can click
your green background to sample it, and drag the
Similarity slider to adjust the tolerance.
You should see the green vanishing to reveal your
new background. Once you have it the way you want
it, stretch the transition to the desired time span,
then render and save.
Other software will take you through steps very
similar to those described above. To learn more
greenscreen theory, try
philipwilliams.com/green
screen.aspx. For an instructional video dramatizing
the greenscreen process, check out
makezine.com/
go/green.
There’s really no need for dull video backgrounds
when you can key your own!
Bill Barminski is an artist, videographer, and lecturer in the
Film Department at UCLA.
