Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 112

The output pull-down menu for Merge1 was set to RGBA (the default). You can
change that if you want the output to be placed elsewhere. The result of the mul-
tiplication of the Lgt and Col passes is now the RGBA. You want to add the Inc
pass to that.
9. From the A Channels pull-down menu, choose the Inc channel set.
10. Sinceyouwanttoaddthispasstothepreviouspasses,choosePlusfromtheOper-
ation pull-down menu ( FIGURE 3.21 ) .
Figure 3.21. Merge2's Properties panel should look like this.