Matrox MXO2 PCIe Host Adapter - Manual (Page 157)

133
Creating a chroma key or chroma key shadow effect
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Show Key Click this button to display the matte used to create your key
effect. This enables you to further refine your key. For example, when you
display the matte, your key color (such as green) appears as black, and
opaque areas appear as white. If you notice some white spots that you
want to key, you can adjust the key controls until the undesired white
spots disappear.
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Auto Key Click this button to automatically key on the most common
color at the current frame in your clip (except gray).
For details on selecting key colors within the graph or performing an auto
key, see
“Using the chroma key graph to modify key colors and perform an
auto key” on page 135 .
¦ Note You must expand the Graphical property in order to see the indicator
when adjusting the chroma key controls.
• Hue Use this to rotate the indicator around the perimeter of the color
spectrum so that you can select different hues (colors) on which to key.
• Aperture Use this to widen or narrow the aperture of the indicator to
increase or decrease the range of colors on which you want to key.
• Saturation Use this to select colors that have a particular saturation value.
Pale colors have a low saturation value and are located at or near the center
of the spectrum. Vivid colors have a high saturation value and are located at
or near the perimeter of the spectrum. Because pale colors have low
saturation, you’ll find them more difficult to key on than the vivid colors.
• Saturation Threshold Use this to proportionally increase or decrease the
region outside of your saturation range. This controls how closely the
Saturation value must match the key color before a region becomes
transparent.
For example, after applying a chroma key effect to a foreground image that
includes dark areas or shadows that you want to preserve in your effect, you
may find that these areas have become semi-transparent. By adjusting the
Saturation Threshold , you can eliminate the key color from these dark
areas, so that they’ll become completely opaque.
• Softness Use this to soften the edges of your key by blending parts of
your foreground image with your underlying image. This makes certain
areas of your foreground image partially transparent instead of completely
transparent or opaque.
• Spill Removal Use this to remove the contamination (spill) that your key
color may leave on or around the edges of your foreground image. Spill is
usually caused by light reflecting from your solid color backdrop (key color)
onto your foreground image.
Spill Removal replaces your key color from
the “spill areas” with the opposite color in the spectrum, which returns a
more natural look to these areas.