Note
If the mask requires adjustment on more than a few frames, delete it and draw the
mask again.Keying out the sky with Keylight (1.2)
Now that you’ve masked the sky, you’ll key out the blue in the area that you masked. First,
you’ll duplicate the layer, and then apply mask modes to isolate the mask.
1. Go to 2:02. Then, select the Close Shot layer, and choose Edit > Duplicate.After Effects adds an identical layer, named Close Shot 2, above the Close Shot layer.
2. Select the Close Shot layer, and choose Subtract from its Mask Mode menu.
3. Select the Close Shot 2 layer, press M to display its Mask properties, and choose Add from
its Mask Mode menu.When you apply the Subtract mask mode, the influence of the mask is subtracted from the masks
above it in the stacking order. The Add mask mode adds the mask to the masks above it. In this
case, you’re ensuring that only the sky will be selected in the Close Shot 2 layer. If you zoom in
to the Composition window while no layers are selected, you can see a faint line where the two
layers intersect.
4. Select the Close Shot layer, and press the M key twice quickly to show all of the mask
properties for the layer. Reduce the Mask Expansion value to –1.0 pixel.The Mask Expansion setting determines how far, in pixels, from the mask path the influence of
the mask on the alpha channel extends. You’ve shrunk the mask on the Close Shot layer so that
the two masks don’t overlap.
5. Hide the properties for the Close Shot layer.