One of the most often asked questions is, “How do I get all of these little jaggies off of the edges of my Chroma-keyed subject?”
And the popular cure-all seems to be the proper lighting of your Chroma-key blue wall (or back-drop). Not just a wimpy little 100 watt
light aimed somewhere in the general direction of the background, but a host of lights that literally flood the background.
We’re talking a minimum of two 250 watt quartz halogens aimed at the backdrop from high and off to each side so that they will not
inadvertently cast any shadows from your key subject (who should be standing at least three feet out from the backdrop).
The key subject should be illuminated with it’s own key light (another 250 watt plus) that is preferably diffused with either an umbrella or a diffusion filter.
If your camera and Panasonic MX-50 video mixer will not recognize your background as a solid, evenly lit blue, then the Chroma Keying will go
crazy trying to determine where the background ends and the key subject begins.
Hence, the “jaggies.”
Every now and then, the background color of blue will reflect back onto the key subject. And this, of course, will cause background video to be keyed in onto the key subject, which you don’t want to do.
This reflected blue can be mostly eliminated by placing light colored amber gels over your background lights (the two lights that flood your
backdrop). More specifically, ask for “bastard amber” at your local photo shop when purchasing these gels. They’ll know what you’re talking about.
As for the key subject light, place it about three or four feet off to one side or the other of the camera so as not to cast any direct shadows onto the background.
Once you have adjusted your “hue” and “slice” control on the Panasonic WJ-MX50 for optimum Chroma-key effect that you view on your monitor,
slight adjustments of the angle and location of all of your lights will make the effect that much better.
Chroma Key Lighting Techniques Revisited
In an earlier issue of MX (above) we discussed the lack of lighting on your blue background which often resulted in “the jaggies”. Be aware
that too much lighting (i.e. two or three 1200 watt lights) could cause problems as well.
Over-lighting the background could turn perceived blue into an almost white color, which of course won’t work properly with the Chroma Key section of the Panasonic MX-50 or the Videonics MX-1.
Obviously, lighting distances and other factors like ambient light will vary from one person’s studio to another. So, experiment with various
lights, gels, diffusers, and distances until you obtain the perfect combination.
Remember, Chroma Key is much more than just a “turn it on - turn it off” feature on a digital mixer. It is an art form and a science in itself
that requires a lot of work on your part to perform effectively. And don’t forget to white balance the Chroma key camera. If it doesn’t see
true Chroma key blue, neither will your digital video mixer.
Learn more about the Panasonic MX-50, MX-30 and AVE-7. Check out our instructional videos in our Online Catalog.
Chroma Key Tricks
What if you want to key yourself in front of a very large background, such as a skyscraper or mountain, and your blue or green backdrop is only about 8 feet by 6 feet?
Well, you could get a larger backdrop that would dwarf you in comparison. Or you could just miniaturize yourself electronically.
Begin by creating a Picture-In-Picture (about 1/9th size) with you and your blue backdrop inside of the P-I-P. On the outside of the P-I-P,
select Background Color as the image that surrounds the P-I-P. Referring to the instruction manual, create a “custom” background color that
identically matches the color of the backdrop in your P-I-P. What you’ll see on the screen is a little tiny you in front of a very large backdrop.
Now record this image onto a video tape and take that tape out and put it into your playback (source) VCR. With that tape now playing as the
incoming source, set up your Chroma Key and let that gigantic backdrop be filled in with Mount Everest or the Empire State Building.
Since most video mixers can lock onto virtually any background color as a backdrop, try setting up a multitude of colors on your studio wall and
set up the Chroma Key to reveal the keyed image through all of the color (by moving the cursor about the screen and pressing “OK”).
Now, with someone in front of the multi-colored wall, begin panning your camera from left to right and back again. What you will see is portions
of the background image revealing and un-revealing itself (even though it will not appear to be moving). What you’re doing is deliberately
confusing the video mixer setup so that it will only reveal a background when it’s right on axis with the pre-registered color. Truly a bizarre effect.
Kill the “Jaggies”
If you’re picking up jagged edges off of your keyed in subject, it’s usually because the backdrop color is somehow bleeding onto your subject.
The first thing to do is move your subject away from the backdrop. Then make sure that your diffused lights illuminating the backdrop are not
creating shadows out of your foreground subject. And then make sure that you are not trying to key in a shinny object, such as a silver-colored
model airplane (which will allow your backdrop to “bleed” all over it causing jaggies). For shinny things, such as metallic objects or bald
heads, try some of the matting sprays available from art supply stores (i.e. Glare-Away) which should take out most of the shinny objects reflective qualities.
Another “color bleeding” problem solver for Chroma Key is the use of amber-colored gels over your backdrop illumination lights. These gels
will have a tendency to absorb the bleeding characteristics of the color blue (which is the color most people use for Chroma Key backdrops).
Play around with the Chroma Key section. See if you can come up with a few effects and tricks of your own.
At The Movies - Chroma Keying.
I believe Forrest Gump, said, “Digital mixers are like a box of chocolates. You never know what you’re going to get.”
I’m often asked, “Where can I pick up some ideas for using my digital video mixer?” I tell them (after they buy my instructional video tapes, of course) to go to the movies.
When you think of special effects on the silver screen, you recall artists like Steven Spielberg or George Lucas because their effects are
great and very obvious. However, when the special effects are so brilliantly performed that you don’t even realize that you’ve been
fooled, then you’ve experienced fantastic special effects. Such as the case with the hit Forrest Gump.
How did Tom Hanks shake hands with JFK, Lyndon Johnson and Richard Nixon?
How did the floating feather in the opening title sequence float right down to Hanks’ feet?
And how did Gary Senise (“Lt. Dan”) become a double amputee for the remainder of the movie?
Simple: Chroma Key. Or “blue screen” as they refer to in the movie industry.
If you haven’t tried it already, get some old film or new footage, which can easily be black and white. Use this footage as your background
footage while you stand in front of your Chroma key blue (or green) wall or backdrop. And on the foreground, or key channel of your Panasonic
MX-50, MX-20, AVE-55, Videonics MX-1, MX-PRO or Sony FXE-100, use your digital effects section to turn the video signal of yourself into monochrome (black & white).
Now join Humphrey Bogart for a drink in Casablanca. Or climb on the Stagecoach with John Wayne. Or even sit on the loveseat with Marilyn Monroe in Gentlemen Prefer Blondes.
If you want a feather to float right down to your feet, videotape yourself sitting on the bus bench like Forrest Gump and use that footage
as your background video. And for your foreground video, attach a feather to a blue thread and dangle it in front of your blue backdrop.
Now just watch your video monitor as you lower the threaded feather to your pre-recorded feet.
Body parts can be removed by merely wearing, let’s say, a blue glove while you’re standing in front of your blue backdrop. Blue tights worn
on your legs will make them vanish as well. Or, how about attaching a round piece of blue cloth to your chest to give the illusion of a rocket just passing through you.
Just give in to the fact that if you see an effect at the movies that appears too far-fetched to be true, first of all, it is. And second of
all, it’s probably Chroma key. Imagination is the key here. So go to the movies. Have some popcorn and get lost and escape from reality created
by the movie masters. Then go home and perform the same effects yourself.
Tip: If you’re shooting video that will later will be used as background footage, try shooting slightly out of focus to give a more realistic
depth of field look. Remember, if your foreground subject is in focus, the background theoretically cannot also be in focus.
And also watch your shadows. If the sunshine on your outdoor background footage casts a shadow to the right, it sure would look funny if your
foreground key subject is casting a shadow to the left.
And once again, a Chroma key lighting reminder: It’s more important to fully illuminate your blue backdrop than it is to illuminate your key
subject standing in front of it. Generally, two quartz halogen lights mounted high on both sides of the backdrop placed about three feet out
from the backdrop do an excellent job of preventing any shadows from being cast by your key subject onto the backdrop. If you haven’t noticed
already, shadows can literally ruin any Chroma key effect.