Ross SYNERGY 4000DR-003, Operation Manual, Page: 205 / 332

Synergy Series Operation Guide (v18) Keying • 7–31
• If spill does occur between the background and the foreground, a blue “halo” or “matte
line” is displayed around the talent’s shoulders and hair. This can be reduced or
eliminated by using a yellow, straw, or amber colored light for the talent’s back light. It
will wash out or neutralize the blue reflection from the background on the back of the
talent. (Note: this technique is not applicable to Ultimatte, as Ultimatte has circuitry
designed to remove blue spill.)
• As a general rule, it is good practice to light the foreground and the background to
approximately the same IRE levels but this is often varied when dramatic lighting effects
are required for the talent.
• And finally, be careful not to mix lights with different color temperatures on the same set
(either foreground or background). The human eye and brain are able to deal with the
subtle differences in color temperatures but cameras aren’t nearly that smart. If you must
use lights with different color temperatures, make sure you use colored gels to
compensate for the differences. Otherwise, you may experience holes in your chroma
key that will be very difficult to remove.
Additional Chroma Key Tips and Considerations
Along with lighting, there are a number of other studio elements that should be taken into account
when setting up your chroma keys. They include, the background material itself, the camera and its
setup, keying from a prerecorded signal on VTR, and using compressed video sources.
• Green and blue are the two most common colors used for chroma keying backgrounds
and are equally effective. Blue was initially chosen because it is the complimentary
color to flesh tone and, therefore, the easiest to key out (we don’t want to key out the
faces, do we …). Given today’s technology, almost any color can be used but blue and
green are still the most widely used.
• There are a number of different materials commonly used as chroma key backgrounds
and each has its benefits. The most common are paper, fabric, and paint. Paper is not as
durable but can be more cost effective and more easily set up than the other two. Paint
takes time and must be applied in several coats to ensure a deep, complete covering,
while fabric also takes time and must be mounted and hung properly. Contact your
lighting distributor for details on the material that best meets your budget and
application.
• If you are creating your chroma key on a studio set, it is generally accepted that the
quality of your chroma key is directly related to the quality of the camera shooting the
scene. The background video can come from any number of sources and may be quite
acceptable but the foreground video is what is being keyed and where your attention is
most focused. Therefore, the camera must be as high a resolution and low in noise as
your budget will allow. In the end, low cost cameras may never produce “acceptable”
chroma key results no matter how well the lighting has been configured.
• Always use the SDI and not the composite output of your camera as your chroma key
source. Composite outputs are considered lower quality, not broadcast, outputs and lack
sufficient luminance and separation to achieve an acceptable chroma key.
• As well, never shoot a chroma key with the detail turned on in your camera. Detail adds
noise to the video signal and makes it much more difficult for the chroma key circuits to
process the video. Turning on the camera detail is not the solution to a low light level –
more lights are!
• And finally, a few other points for your consideration. Avoid using foreground chroma
key sources from 4:1:1 formats, highly compressed material (more than 4 to 1), or