[Class Assembling] Hi! John Hess from FilmmakerIQ.com. In the
greenscreen history lesson I talked about the processes filmmakers have used to make
traveling mattes - in this lesson I'll dive into the necessary elements you need to pull
off a great chromakey. The first element in pulling off a key is
the type of space you have to work with. Your space will determine what kind of chromakey
shot is possible. When shooting against a greenscreen or a blue screen, you'll want
to pull you subject away from the background far enough so that shadows don't fall on
the screen and you'll want to minimize the reflection of the screen on your subject. With smaller spaces you should be able to
pull off a reasonable talking head shot - that's where the shot is just the head and shoulders
of the subject speaking. For a full body shot, you're not only going to need a larger space
for a screen, but some distance to place the camera so that your subject looks natural
and isn't distorted by a wide angle lens. Shooting outdoors is also a possibility especially
for certain shots, just keep in mind you'll have to deal with all the issues that come
shooting outdoors including wind, noise, and shadows. The first question you're going to ask is
green or blue? Blue screen was a traditional color in the film days and is still used today
for many productions, but green is the preferred color for digital keying. Why? Because many
digital cameras use a Bayer pattern of Red Green Blue photosites where there are twice
as many green photosites as there are red and blue. This makes digital cameras much
more sensitive to green coloring. Green screen also requires a lot less light than blue screen
and is less likely to match the clothing of your actors. Still you may want to use blue screen in certain
cases - say you're shooting a green monster. In fact on the Sam Raimi's Spiderman, The
Green Goblin had to be photographed on a bluescreen because the suit would have been lost on a
greenscreen. Spiderman on the other hand had to be shot on a Greenscreen, because his suit
was red and blue.. When it comes to the material of your screen
you have several options. The first is to paint your background using a chroma key paint.
This is the most permanent although labor intensive way to create a chromakey background
though certainly necessary if you are planning on installing a cyclorama. The other option is to hang your screen You'll
need background stands and clamps to hang your screen on. The screen itself can be made
out of paper, or muslin background clothe, but I prefer foam backed cloth because it
scatters the light more evenly so you can avoid hotspots and the foam keeps the screen
from wrinkling when not in use. For small setups, foldable chorma key screens
are available. These kits are really handy for quick portable setups or outdoor use and
built in frame keeps the screen from getting too wrinkled. When lighting for chroma key you have to think
of lighting first for the screen itself and then for the subject. In tight situations
you can combine the lighting but you could end up with shadows on your screen and that
will make for a much more difficult task of pulling a good key. Start by focusing on getting a clean and even
light on your screen without your subject. Here I'm using 2 ikan IDMX1500B dual color
fixtures - part of the ikan 5 piece dual color chroma key kit. These are hung in front of
the screen using a truss system. These are awesome LED lights that put out a lot of soft
even light which is an absolute must properly lighting a greenscreen. Now if you're an avid DIYer you may try
to use long fluorescent tubes to light the screen. Another DIY option, is the Hollywood
strip lighting fixture - this one I found on a street curb being thrown out - and it
made a nice shadowless screen light. To check to see the quality of our lighting
on the greenscreen, I'm using the ikan MD7's built-in waveform monitor. Notice the tight
band.. This means that are screen is evenly lit and there's not much variation on the
screen itself. You want to get this band as tight as possible, not slanted or have spikes
which are hotspots.. If you can't get your hands on a waveform
monitor, you can use your camera's zebras settings. Zebras tell you what part of your
image is overexposed, if you lit your screen properly you should see the entire screen
turning into zebra stripes at once as you open your iris to over expose the screen. Once we have a well lit screen it's time
to put our subject in place and work on the subject's lighting. Keep in mind the final
composition and try to light your subject that will match the scene you're attempting
to composit.. Here I'm using the ikan IB1000 LED lights
- part of their chroma key kit. These lights can be set to 3200k which will match great
with the tungsten lights I already own. Just take care when lighting your subject to avoid
casting shadows on your screen. When I first started experimenting with greenscreen,
I was working with DV in standard definition. You had to be exact in order to get an acceptable
key, and even then there were some funky artifacts. But I'm happy to say that with HD, getting
a reasonably acceptable key is much easier because the pixels are so much smaller. But
the type of compression can be a detriment to quality greenscreen. Most consumer cameras use a 4:2:0 compression
for handling color - I talk more what color compression is in the lesson on Non-Linear
editing if you want a refresher. 4:2:0 throws away a lot of color data that can be very
useful for achieving a quality key. In this demonstration, I'm using the Blackmagic
Cinema Camera decked out with ikan's DSLR Rig. The Blackmagic Cinema Camera is capable
of recording in 4:2:2 compression using ProRes or DNxHD formats or even recording 4:4:4 uncompressed
12 bit raw. My tests have shown that the compressed 4:2:2
is pretty good for pulling a good chroma key but the RAW is simply unbeatable in terms
of ease and quality. If you want the best chroma key, by all means shoot RAW - just
know that it is expensive in terms of the amount of memory it eats up. I'm not saying
you can't pull a decent key using anything less than 4:2:2 color compression or RAW as
in the Blackmagic Cinema Camera, but a camera like this with it's compression or lack
thereof sure makes a the key a heck of a lot easier. Most of the basic keyers you find inside NLEs
behave like hardware chroma keyers in that you'll most likely be let down by the results.
But there are a lot of professional keying software solutions available out there that
can help you pull pretty good keys even out of so-so footage. My favorite. happens to
be one that comes bundled inside of Adobe After Effects called "Keylight" made by
The Foundry. This plugin is incredibly robust with all kinds of features like matte choking,
spill removal, de-spotting- and even masks that you can apply to fix little chroma key
mistakes here and there. Plus After Effects is just a good platform to be working doing
your compositing in the first place. Keylight is also available for purchase for other editing
platforms. Now if you can't pull a perfect key off
the entire frame - don't worry as there is a technique called garbage matting. Using
After Effects, you can create a rough mask around your subject and throw away all the
other junk in your frame thats unimportant. This is a great way to work in smaller spaces
- just make sure you subject does cross into the garbage matte Once you have a good clean key, it's a matter
of compositing the subject into your background plate adjusting the color to match, and compositing
foreground elements to really sell the effect. By considering your working space, using a
quality screen, lighting it evenly, using a camera with as little compression as you
can get, and finally using a good software keyer, you should be able to pull off a great
key. Good chroma keying is a skill, and it will take a little practice, but the reward
for your patience and experimentation can be quite liberating. - Another tool for you
use in your quest to make something great. I'm John Hess, I'll see you at Filmmaker
IQ.com
