Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 109

Working down the pipe
To start layering passes, first combine the Lgt and Col passes with a multiply operation.
Let's connect a Merge node.
1. Select Crop1 and insert a Merge node after it by pressing the M key.
Merge1 has two inputs. The B input is not connected. You want to combine two
differentchannelsetsthatliveinsidetheRead1branch,soyousimplyconnectthe
B input to the same output that the A input is connected to—the output of Crop1.
2. Move Merge1 below Crop1 and connect Merge1's B input to Crop1 ( FIGURE
3.16 ) .
Figure 3.16. Both the A and the B inputs are connected to Crop1.
So how are you going to tell Merge1 to use different channel sets for this oper-
ation? So far you have been combining the RGBA of images, which is the de-
fault state of the Merge node. However, you can change that using the pull-down
menus for each input ( FIGURE 3.17 ) .
Figure 3.17. The pull-down menus control which channel sets are combined.