NewTek TriCaster Advanced Edition User Guide - Manual (Page 147)

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13.2.2 TOLERANCE
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.
13.2.3 SMOOTHNESS
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’.
13.2.4 LUMA LIMIT
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 by the subject’s choice of 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 the background color. In
simplest terms, problem areas of this type can be decisively ‘pulled’ back into the foreground by pre-filtering
the chromakey effect around a luminance threshold.
Generally, try to set up the best key you can before raising the Luma Limit from its default value of zero (no
effect). Then gradually raise the limit until you are pleased with the result.
SECTION 13.3 SPILL SUPPRESSION
The term ‘Spill’ refers to key color unintentionally reflected or ‘spilled’ onto the foreground subject. For
example, a little green spill often appears on the shoulders of someone in a greenscreen shot.