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Video Mix/Effects
Extra Chroma Key Controls
key. If the foreground subject is stationary, consider using a force mask instead of
increasing selectivity.
• Chroma suppression can be set accurately with Auto Setup. To adjust, increase Chroma
suppression and observe the backing color dot on the vector scope move toward the
center. You want to center it exactly, so no chroma exists in the backing area. 100%
chroma suppression is the correct setting for all chroma keys. At this point, you will
probably see a line through the center of the vector scope. With increased selectivity,
this line will become an arc.
• Luma suppression adjustments may be necessary if shading is visible in the backing
area with FG Only selected, or if the shading adversely affects the background image.
Primary Luma suppression is hardly ever desired when Reshape is on. To adjust,
increase Luma suppression and observe the backing color move toward black. You
want to make the backing color just black. Increasing this control too much will make
the chroma key hard and noisy. When not enough, highlights will be added to the
background. Note that incomplete luminance suppression is not necessarily bad. The
highlights added to the background will match the shading on the backing wall,
adding natural shadows and perhaps eliminating the need to add artificial shadows.
• All the above adjustments may need to be revisited later.
Another potential artifact of chroma keying is a tinting of the overall foreground subject
due to lighting splash from the backing color or lens flare.
Flare Suppression adds a small
amount of color to the entire foreground image to cancel the splash or flare. Typically less
than 2% of the backing color is needed to neutralize the flare.
Extra Chroma Key Controls
Additional chroma key controls are available by selecting the stage 4 Extra Controls data
pad. Coring, fringe, and shadow controls can be individually activated by selecting the
labeled buttons.
Six Keyer System Example
Coring replaces any pixels in the luminance signal after primary suppression that are below
the adjustable threshold with black. This eliminates noise resulting from incomplete
suppression. While coring can improve some keys, it can easily be over done. Coring