NewTek TriCaster 855 - Manual (Page 208)

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TOLERANCE 11.2.2
No physical greenscreen is perfectly comprised of one color. Wrinkles, folds and shadows along
with the seemingly inevitable uneven lighting result in difference. For this reason, TriCaster
provides a numeric slider labeled Tolerance just beneath the Color picker.
The Tolerance setting allows you to broaden the range considered as the key color, including
more ‘near-neighbor’ colors to be included in the matte. A low tolerance removes only color
values close to the primary or key color. As you raise the tolerance, you extend the range of
values on either side of the primary color that will be treated as transparent. This allows you to
deal with those imperfections we mentioned.
On the other hand, it may be that there is (usually unplanned for) detail in the foreground that is
somewhat similar to the key color. Reducing Tolerance may allow you to prevent unwanted
holes appearing when the subject opts to wear his St. Patrick’s Day tie.
SMOOTHNESS 11.2.3
Smoothness defines a further tolerance factor, and a very useful one. We want our keyed
foreground to blend smoothly into the background – rather than to stand out in hard relief like a
postage stamp or decal. Smoothness serves this purpose. Don’t overdo it though, as aggressive
settings can cause the foreground to become unnecessarily ‘muddy’.
LUMA LIMIT 11.2.4
When working with poorly-lit backgrounds (or poor quality footage), the color Tolerance range
separating the foreground (talent) from the background can be extremely narrow. This problem
can be aggravated if the subject wears dark clothing, or when there are harsh shadows; there is
often a strong chroma component (and associated chroma noise) in dark foreground areas. The
‘noise’ may be partially or completely transparent when tolerances are critical. Because the
noise varies over time, ‘holes’ in the foreground can result, and even worse these may flicker on
and off from one frame to another.
LiveMatte’s Luma Limit control makes it possible to overcome this issue. In essence, it restricts
the chromakey operation based on luminance (brightness) values. Dark foreground areas which
typically cause the problems just described normally have quite different luminance values from