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Viewing the key
The first step in fine-tuning the keyer settings is to see what the key looks like. Two measures
that will help you see the key better are zooming in on a trouble spots and switching to a
neutral background. For information on panning and zooming the view in the monitor, see
"Magnifying and repositioning the view in the monitors" on page
Switching backgrounds
Switching temporarily to a pure white, pure black, or checkerboard background can help you
detect and eliminate imperfections in the key. For your convenience, these useful backgrounds
are built into the Background layer thumbnail. Right-click the Background layer thumbnail,
and try the different options to see which one best reveals various problems. In general, black
and white work help you check the key along the edges and isolate imperfections in the input
clip's background, and the checkerboard backdrop helps you detect an unwanted
transparency.
To change back to the desired background when you're finished changing the keyer settings,
right-click the Background thumbnail, and choose Reassign Last Source to retrieve the
original image.
For most keyed scenes, a pure white or black test background represents the most
challenging possible keying situation. You can use these backgrounds to tune the key
more precisely than you can with an actual background. However, trying to eliminate all
of the shading or noise in the video can be a frustrating and impossible challenge and
can actually yield less appealing results than leaving the key a bit less than perfect. This
is because achieving a perfect key can require extreme settings that reduce the quality of
the overall appearance. For example, removing the last hint of green in the subject's hair
can result in a loss of definition along the edges.
When viewed against a real-world background, minor flaws in the key are usually not
visible. Therefore, Adobe recommends that you use the white and black test
backgrounds only for broad changes, and then use the actual background over which
the clip will be composited to fine-tune the settings. If you later change the background,
you may need to readjust the key.
Basic keying workflows
This section suggests a sequence of steps to fine-tune a key. The order of the steps is important
because various settings on the Keyer tab interact with one another. Proceeding in a different
order may result in taking one step forward in one regard, only to find that you've moved back
two steps in another regard.
33.
Setting the key
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