User Manual

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Before (top) and after setting up a sky replacement by connecting an HSL
qualifier of the blue in the sky to the Alpha Output to create transparency
This procedure works equally well with still images or movie clips. Also, depending on
the range of motion you’re going to be matching, you’ll probably need to use a
background image that’s somewhat larger than the region you’re keying, to make sure
you have full coverage as the layer moves to match the foreground motion. If
necessary, you can zoom into the image using the Zoom parameter in the Transform
section of the Edit page Inspector.
3 In this example, the foreground clip happens to have a camera pan, which gives the
composite away as the sky doesn’t move along with it. To move the compound clip of
the sky image to match this pan, open the Tracker pallet.
4 Choose its Stabilizer mode, and then click the Analyze Forward button to analyze the
motion of the entire clip. Then, click the Tracker palette’s Option menu, and choose
Copy Track Data.
5 Select the clip that you want to match (in this case the sky image), then open the
Tracker Palette’s Option menu and choose Paste Track Data.
6 Now, for this to work correctly, you need to set the Strong parameter to –100, and click
the Stabilize button. Setting a negative value inverts the tracking data you copied in
step 3, which enables it to become a match move. If you’re feeling extra tricky, you can
set the Strong parameter to a little less than –100, say –94, which introduces a disparity
of foreground and background motion that simulates parallax.
Inverting the Strong parameter with a negative number to create matched motion
At this point, playing through the clip should result in a nicely matched correspondence
between the movement of the foreground and background layers.
Chapter – 133 Sizing and Image Stabilization 2987