Channel Nodes
Channel nodes deal with the use of channels and layers within your composite. Typical channels are red, green, blue, and alpha - however, there are many other pieces of useful data that can be stored in unique channels. A layer is simply a collection of channels, for example rgba.
Adds channels to the input image.
Merges one channel from each input and saves the result in an output channel.
Replaces channels in the B input with channels from the A input.
Removes channels from the input clip.
Rearranges up to 8 channels from a single input or between two inputs.
Rearranges up to 8 channels between two inputs.