The Split color map node splits the red, green, and blue channels of an input color mask and outputs a mask from each of these channels. Each channel with values between 0 and 255 is normalized to be stored in a mask.
The inverse operation is provided by the Color map from masks node.
To add a Split color map node, right-click in the Graph Editor and select Create Node > Color > Split color map.
This node has no parameters.
Use the Fast-creation menu by clicking and dragging the input connector to find compatible color map nodes.