Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 115

One of the interface elements you're going to use a lot is the Dot. The Dot is a circular
icon that enables you to change the course of a pipe, making for a more organized tree.
1. Select Crop1 and press . (period) on your keyboard.
2. Select the newly created Dot, and then insert a Shuffle node from the Channel
toolbox.
3. MakesureyouareviewingShuffle1intheViewer,andthenchangetheIn1prop-
erty to Lgt.
4. From the In 2 property's drop-down menu pick RGBA instead of None.
5. Check the In 2 alpha to alpha check box to direct the alpha from input 2 to the
alpha output ( FIGURE 3.24 ).
Figure 3.24. Using Shuffle you can mix channels from multiple channel sets.
What you did here was take the R, G, B from the Lgt channel set and the alpha
from the original RGBA channel set, and output these four channels into a new
RGBA. You did this so that your Lgt pass, which doesn't come with an alpha
channel, will have the correct alpha channel.
Because you will do this a lot, it is a nice reminder if you name your Shuffle1
node according to the name of the input channel set. You can simply change the
nameofthenode,butthatislessadvised.Instead,youhavealabelforeachnode,
accessed via the Node tab in each node's Properties panel.