Graphics Programs Reference
In-Depth Information
16. Hover your mouse pointer over the Viewer and press the A key to view the alpha
channel.
Tip
For fine-tuning, select a point and use the number pad on your key-
board to move the point around. NUM2 is down, NUM7 is diagonal
left and up, for example. Holding Ctrl/Cmd reduces the move by a
10th, and holding Shift increases by 10.
You have now created your first matte!
17. Press the A key again to view the RGB channels.
Compositing with the KeyMix node
You will use another type of layering node than the usual Merge node here, just to spice
things up. The KeyMix node has three inputs: a foreground, a background, and a matte.
Unlike the Merge node, the KeyMix node accepts a non-premultiplied (unpremultiplied)
image as its foreground image. It's very convenient to use the KeyMix node to mix two
imagesthathavenomatte.Itwouldhavebeenperfectforthesplit-screenexerciseyoudid
earlier, although I wanted you to try both options. But you would save two nodes using
a KeyMix, as you wouldn't have to use a ShuffleCopy or a Premult node. You will use
KeyMix now instead.
1. Select Blur1 and from the Merge toolbox click KeyMix.
2. ConnectKeyMix1'sBinputtoRead1,andtheMaskinputtoRotoPaint1( FIGURE
6.57 ) .
Figure 6.57. Connecting KeyMix's three inputs.
 
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