To view this page ensure that Adobe Flash Player version 11.1.0 or greater is installed.
An editor’s perspective:
Chroma-key by Larry Jordan
W hen it comes
“green-screen key”) the
phrase “Don’t worry, we’ll
fix it in post.” is a recipe for disaster,
because if you don’t shot your key right
during production, it will be painful, time-
consuming and expensive to fix it later
I know, because I’m an editor. Bad
chroma-keys are a train wreck and it isn’t
even the editor’s fault!
Pulling (“creating”) a high-quality key
starts with a bit of planning before
the shooting even starts. Since this
is a “Studio Issue,” let’s talk keys and
What a chroma-key does is select a
specifi c color, generally green but it could
be any color, and make it transparent.
When shot and lit properly, this allows
us to replace a green background
behind an actor with an entirely different
background. Piece of cake, right? Sigh... Nope.
The key phrase is “select a specifi c color.”
The problem is that many production
crews think close enough is good
enough. And it isn’t.
Planning your production
The best thing you can do to improve the
quality of your keys is to improve how you
shoot and light them. Here are nine rules
for green-screen production:
1. The green screen background
should be as smooth as possible;
ideally, painted on a smooth surface.
Never paint green on a textured
background. If you are using fabric,
iron out folds or ripples and stretch it
tight. 3. Light the green screen evenly from
top to bottom and from left to
right. Ideally, the green should land
between 40-50% on a Waveform
Monitor. 4. There is NO relationship between
how the background is lit and
how your actors are lit. Light your
background for smoothness. Light
your actors for drama. Never light
actors with the same lights you are
using to light the background.
5. Actors should be at least 10 feet in
front of the green screen. This avoids
light from the background “spilling”
around their body or shoulders,
creating a blurry edge.
6. In general, don’t have actors cast
shadows on the green screen. Be
very careful shooting feet. If you
need to deal with shadows and
feet, expect to pay MUCH more for
software to key them cleanly.
7. The green background does not
need to fi ll the frame, but it DOES
need to completely surround the
edges of your actors. Editors use
garbage mattes to get rid of the junk.
8. NEVER shoot interlaced video for
your green-screen (foreground) shot.
Always shoot progressive. Interlaced
edges are very, very hard to key.
(And, don’t worry. It is easy to convert
a progressive clip to interlaced after
your effects work is complete.)
9. It is often better, but not required, to
shoot a higher-resolution image as
the green-screen foreground shot,
then reduce the image size during
editing. For example, shoot 1080p,
then edit in a 720p sequence. This
can often improve edge detail,
chroma saturation, and the ability to
create a cleaner key.
Catastrophe in practice
Let’s compare two chroma-
key shoots: one where it
was more important to “get
it done” than to get it done
right, and the second where
a bit more time was taken to
make the key look as good
as it could on set.
The image below is our fi rst
example. (Sorry, but I don’t
have permission to show the
Look at how many of our
“Key Rules of Production”
• There are multiple
shades of green.
• The green is
very unevenly lit;
ESPECIALLY around the
There is almost no color
in the frame; it is very
There is motion blur on
the performer, making
edges hard to determine
• The performer is casting
shadows on the green
• There is all kinds of junk
in the frame
• The actor is lit using
the same lights that are
attempting to light the
background The only good news is that
the green screen behind the
performer doesn’t have any
folds or ripples. Um, yay.
2. The exact shade of green does not
matter. What DOES matter is that all
the green be the same color. (And it
goes without saying that your actor
should not wear any colors even
close to that shade of green.)
40 | TV-BAY MAGAZINE: ISSUE 92 AUGUST 2014