Customizing Nuke with Gizmos - Nuke 101: Professional Compositing and Visual Effects - page 514

6. Connect Rectangle1's and Rectangle2's inputs to the output of ColorBars1.
OK, so now the resolution will be correct since the Rectangle nodes will draw
around the input resolution. But you don't want to actually use the color bars im-
age as part of the Safe Area tree. If you select the Replace check box, only the
resolution of the input image will be outputted but the actual image won't be (it
will be replaced by the image generated in the node—in this case a rectangle).
7. In Rectangle1's and Rectangle2's respective Properties panels, select the check
box called Replace.
The problem is now fixed. Whatever resolution you bring into this tree will
change the size of the Safe Area boxes.
Noticethatyourtestimagehasthreeoutputs.Sincethisimageissomethingyou'll
need to replace constantly, it would be a good idea to have only one output.
8. Click ColorBars1 and press . (period) on the keyboard to create a dot.
And there you have it. The next stage will be to wrap this tree up in what's called
a Group.
Wrapping in Groups
A Group in Nuke is a node that holds another tree inside of it. You can still access what's
insideofitandmanipulateit,butyoucanalsotreatitasoneentity.It'susefultowraplittle