This function allows switching the color channels of an RGB or CMYK image
Source is the source channel. Destination is the destination channel.
You can select one of the color channels (Red/green/blue or Cyan/Magenta/Yellow/Black), File or Clipboard. Especially Clipboard is a fast way to make a color channel a layer or a mask of another layer.
File as source loads a channel and File as destination saves a channel. If you are loading a channel, it has to have the same size as the image.