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Because decoding DV in real time requires a lot of processing power, Adobe recommends
that you use a fast computer. On slower computers, you may need to lower the Resolution
value, which controls the preview resolution.
Some video cameras output thin black bars in the overscan areas on the right and left
edges. You can change the Underscan value in Ultra to delete these bars. Ultra stretches
the image by the specified amount, preserving the frame aspect ratio of the live input. This
setting applies only in Live Preview mode.
Setting up the camera
You should always disable automatic color settings on the camera when shooting for color
keying. Otherwise, the background's brightness or hue may change when on-camera subjects
move across the frame. Adjusting the camera manually, try to match the intended virtual
background as closely as possible by adjusting the iris, white balance, shutter speed, and other
camera-specific parameters.
Ultra works best when the camera is locked down on a tripod. In most modes, Ultra uses a
static model of the background. If the camera moves, then the model will not remain aligned
with the variations in the background. If a clip involves any camera movements, then the only
way that you can key it in Ultra is with the single key point method, which works entirely by
color without a model. For more information, see
Pickup)" on page
79.
Controlling the lighting
Controlling the lighting of the foreground scene helps you to achieve realistic results. The goal
is to adjust the foreground to match the intended virtual background. Analyze the intended
background—either a virtual set or your own still image or video clip—to determine the
direction of the primary light source for the background scene. Position the lights at the same
relative positions so that the subject receives the same general lighting as elements in the
background. For example, if the background is strongly lit and leaves hard shadows and shiny
highlights, then you want comparable lighting on the subject in front of the color screen.
Getting the subject's shadow right can significantly enhance the realism of the final
composited shot.
Although you can tune the key to preserve shadows from the input clip, you can also generate
shadows digitally by using Ultra. This approach has several advantages over working with
actual shadows. Most notably, you can easily control the shadow's position, scale, and opacity
as well as several other attributes. For more information, see
on page
111.
58
How to
"Single Key Point Method (One Color
"Adding shadows and reflections"
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