place the chroma key over. This source
is used for the automatic adjustment of
the chroma key.
• Press
Auto Edge Luma
to have the edge
luminance automatically adjusted, based
on the replacement background.
• Press
Auto Re-Spill Color
to have the
re-spill color automatically adjusted,
based on the replacement background.
UltraChrome Best Practices
High-quality chroma keying with a natural look
is fully-achievable with the UltraChrome 2
keying system. However, as with any chroma
key system, careful attention should be paid to
the chroma key environment.
Keep the following in mind when working with
a chroma key:
• The set should be evenly-lit, with a
reasonable level of brightness, too bright or
too dark will compromise the ability to
produce a great result. High brightness
generates high levels of reflected color
background (Spill) into the foreground
subject. When the camera output is viewed
on a waveform monitor, the background set
level should read between 50-75% of the
overall image level. The foreground subject(s)
should be separately lit.
• Adjust camera shading using appropriate
charts, ensuring that grey scale, lens flare,
gamma, and white/black balance correctly
set. If using the AC-H200-UCHR camera, it is
recommended it be set in HDR mode -
HLG1200. This mode is compatible with
standard (non-HDR) signals and the wider
dynamic range allows greater image
separation in lower-light regions. Also, the
camera should be set at its minimum gain to
ensure the lowest noise levels, and detail
levels should be kept at minimum to avoid
sharp edge transitions.
• Real elements, presenters, and props should
not contain colors similar to the background.
Clothing or props with high reflectivity
should also be avoided to minimize color spill
(colored light reflected from set onto
foreground subject).
Masking
The switcher has a mask available for every key
channel (including chroma keys), plus an
additional mask available to each chroma key
channel. Chroma keys can use static box masks
or dynamic masks from an external source.
Dynamic masks are fed from virtual set systems
(such as Ross Voyager) and follow camera moves
through camera-tracking data provided by
robotic systems.
From the Mask Setupmenu, press
Utility Bus
Mask
and select the input source that has the
mask you want to apply.
The Four Chroma Key Commandments
1.
A Great Chroma Key is Made from a Great
Original Source — Before attempting to set
up the chroma keyer, make sure lighting,
background, and talent all look great on the
camera; and that camera Gain and Detail
have been reduced to a necessary minimum.
2.
No Chroma Key is Ever the Same, Start
Fresh with Init — Every set has its own
lighting conditions, camera and lens setups,
CK wall-quality, consistency of paint,
foreground talent clothing, colors, and skin
tones. The UltraChrome automatic
initialization (
Init
) does not require color
pickers or hue controls; once the general
color vector has been selected, it will
analyze the entire frame and determine the
exact chroma vector and angle of the color
background to be removed.
3.
Init, Try, Re-Init and Try Again — The
fine-tuning required to get a great result is
often minimal and frequently hinges on the
adjustment of a single parameter. Changing
the value of the wrong parameter can make
it impossible to then make corrections with
other controls. When learning the nuances
of this chroma key, re-
Init
after making a
change that does not achieve the desired
result and then try another. Also, all chroma
key parameters are saved in the memory
system, so you can save a setup and then
start over if necessary.
4.
No Last Minute Changes — Once the
chroma set, lighting, and cameras are tuned
for best performance - don’t change
anything! On a normal set, it is common to
make last minute tweaks and changes to
lighting, iris settings, and even
talent/wardrobe. When chroma keying,
these changes will require the key to be
reset and adjusted - which is fine if you have
the time. Avoid change if you can, especially
44 • Keying — Ultrix Acuity Operation Manual (v10.1)