When I start a shot, one of the first things I do is shuffle the source reads RGB channels into a src_plate layer. By doing this I have created a new layer in my compositing stream that i can now get to at anytime. I can also do this with pre-renders of denoised source plates or maybe just the red channel for tracking. These can be shuffle copied into the compositing stream as well. Now when I need the source plate down the compositing stream I can use a shuffle node to bring that layer front and center.

There is a flip side to all these layers and channels. If you work with folks that do not use this method of compositing then this might cause a problem. Above all else when working with others in compositing is to have everyone on the same page. Above all else if you are working within a group keep your scripts readable and organized as you can.

Take some time and understand what your doing. There is nothing worse than not knowing why a image or matte isn't showing in the viewer.

Here is an example script to look at. And also a link to Nukepedia.com explaining more in-depth layers and channels. In this script there is SRCPLATE and SRCPLATE_CC. Both layers containing RGBA channels. There is also a roto node that is plugged into a copy. I am coping the roto nodes matte into the stream for future use.

        set cut_paste_input [stack 0]
version 6.2 v2
push $cut_paste_input
Roto {
 output alpha
 curves {AnimTree: "" {
 Version: 1.2
 Flag: 0
 RootNode: 1
 Node: {
  NodeName: "Root" {
   Flag: 512
   NodeType: 1
   Transform: 0 0 S 0 0 S 0 0 S 0 0 S 0 1 S 0 1 S 0 0 S 0 1024 S 0 778 
   NumOfAttributes: 10
   "vis" S 0 1 "opc" S 0 1 "mbo" S 0 1 "mb" S 0 1 "mbs" S 0 0.5 "fo" S 0 1 "fx" S 0 0 "fy" S 0 0 "ff" S 0 1 "ft" S 0 0 
  }
  NumOfChildren: 0
 }
}
}
 toolbox {createBezier {
  { createBezier ssx 1 ssy 1 sf 1 sb 1 tt 4 }
  { createBSpline ssx 1 ssy 1 sf 1 sb 1 }
  { createEllipse ssx 1 ssy 1 sf 1 sb 1 }
  { createRectangle ssx 1 ssy 1 sf 1 sb 1 }
  { brush ssx 1 ssy 1 sf 1 sb 1 }
  { eraser src 2 ssx 1 ssy 1 sf 1 sb 1 }
  { clone src 1 ssx 1 ssy 1 sf 1 sb 1 }
  { reveal src 3 ssx 1 ssy 1 sf 1 sb 1 }
  { dodge src 1 ssx 1 ssy 1 sf 1 sb 1 }
  { burn src 1 ssx 1 ssy 1 sf 1 sb 1 }
  { blur src 1 ssx 1 ssy 1 sf 1 sb 1 }
  { sharpen src 1 ssx 1 ssy 1 sf 1 sb 1 }
  { smear src 1 ssx 1 ssy 1 sf 1 sb 1 }
} }
 toolbar_brush_hardness 0.200000003
 toolbar_lifetime_type all
 toolbar_source_transform_scale {1 1}
 toolbar_source_transform_center {1024 778}
 view {}
 motionblur_on true
 name Roto1
 selected true
 xpos 3614
 ypos -43
}
CheckerBoard2 {
 inputs 0
 name CheckerBoard1
 selected true
 xpos 3608
 ypos -205
}
ColorBars {
 inputs 0
 name ColorBars1
 selected true
 xpos 3775
 ypos -381
}
add_layer {SRC_PLATE SRC_PLATE.red SRC_PLATE.green SRC_PLATE.blue SRC_PLATE.alpha}
Shuffle {
 alpha black
 out SRC_PLATE
 name Shuffle1
 label "\[value out]"
 selected true
 xpos 3775
 ypos -298
}
add_layer {SRC_PLATE_CC SRC_PLATE_CC.red SRC_PLATE_CC.green SRC_PLATE_CC.blue SRC_PLATE_CC.alpha}
ShuffleCopy {
 inputs 2
 red red
 green green
 blue blue
 out SRC_PLATE_CC
 name ShuffleCopy1
 label "\[value out]"
 selected true
 xpos 3775
 ypos -184
}
add_layer {roto roto.matte}
Copy {
 inputs 2
 from0 rgba.alpha
 to0 roto.matte
 name Copy1
 selected true
 xpos 3775
 ypos -43
}

Enjoy,

michaelb

Nuke gets very powerful the more you use its layer and channel system. Ask any nuke artist and many will say the same thing. It's one of those features that you wonder how you lived without for so long.

Let me explain.

In compositing you have layers and channels. Each layer can have 4 channels. R for red, G for green and B for blue. The 4th channel being the alpha channel. That comes in black or white.

In Nuke you can have more than that. You can make them on the fly as your compositing. They can also come from a outside source such as a 3d application, or even Photoshop.

Everyday i work with source plates that includes and red channel, a green channel and blue channel. The alpha is either black or white. Now things can get fancy. Say I do color correction to the source plate. I also make a clean plate so we can replace/hide an object or talent. Both the clean plate and the color corrected src plate can have its own named layer and channels to go with it.

We can also do this with mattes. We can create a new channel called door.matte. Now anywhere in the compositing tree you can use that channel to control color of anything else you might need.This gets even more cool with normals passes and other fancy images that applications can produce. This topic is for its own post.

Why is this powerful?

This makes for very clean and easily readable scripts for one. You can setup your scripts in batches or groups of nodes an not have have pipes zigzagging in the node graph. Which is nice when you are working with other artists. Rotoscoping nodes on top, tracking and other cleanup under that and so on.

Please feel free to post how you use the Layer/Channel system in nuke. and why its powerful to you in your everyday work.