Customizing Nuke with Gizmos - Nuke 101: Professional Compositing and Visual Effects - page 507

You hard work is paying off. You have two boxes—one for each safe area—and
you can manipulate them using User Knobs.
32. Switch to viewing the RGB channels in the Viewer.
A big white rectangle—that's not what you want at all. You need to move the al-
pha channel into the RGB channels as well.
33. Click Merge1 and insert a Shuffle node after it.
34. Shuffle the alpha channel into all four channels ( FIGURE 12.21 ).
Figure 12.21. Shuffle1's Properties panel.
It's also a good idea to create something that gives feedback in the Viewer about
the size of the safe areas. You can easily do that using Text nodes and some basic
scripting for automation.
Scripting with a Little TCL
TheTCLscriptinglanguagewasthemainlanguageinNukeuntilVersion5,whenPython
scripting replaced it. Nuke can still use TCL, but mostly everything has moved to Python.
A few things have remained TCL by default, mainly Text Input fields. You can practice
this here briefly:
1. Click Shuffle1 and insert a Text node from the Draw toolbox after it.