Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 139

7. Connect Merge10's B input to the final output of your comp (Merge9) and view
Merge10 in the Viewer.
Use this Merge node to combine the Ambient Occlusion pass (here simply called
AO) with the whole comp (the pass affects both the lemming and the floor). Be-
causetheAOpassiswhollywhite,exceptforthedarkpartsrepresentingtheshad-
ows, you'll use the Multiply operation in the Merge node.
8. InMerge10'sPropertiespanel,changetheAChannelproperty'sdrop-downmenu
from RGBA to AO.
9. Change Merge10's operation from Over to Multiply ( FIGURE 3.57 ).
Figure 3.57. This is where Merge10 should be.
Here again you saved a Shuffle operation and did the shuffling inside the Merge.
Youwillcombinethedropshadowpassinaslightlydifferentwayinthenextsec-
tion.
Using the Mask Input
AnothergreatwaytousechannelsinNukeistheMaskinput.TheMaskinputisthatextra
input some nodes—including all the Merge, Color, and Filter nodes—have on the right-
hand side. You can see the Mask input in FIGURE 3.58 .
Figure 3.58. This is the Mask input. It says so when you click and drag it.