The Keyer super tool has three image inputs and three outputs.

Double-click the Keyer super tool node, or right-click the node and select Edit Group to expand the Keyer.

The Front input image is despilled by the Spill & Blend tool node (an instance of the Spill & Blend tool). The result is sent to the Result node (an instance of the Set Alpha tool) to become the RGB channels of the RGBA Output Image output.

The Front input image is processed first by the Screen Degrain tool node (an instance of the Screen Degrain tool), then by the Master Keyer matte generator (an instance of the Master Keyer tool). The resulting matte is then sent to the Cleanup Alpha node (an instance of the Cleanup Alpha tool), then to the Edge node (an instance of the Edge tool), and that result to the Garbage Mask node (an instance of the Garbage Mask tool). The output of the Garbage Mask node is sent to the input of the Result node to become the alpha channel of the RGBA Output Image output, to the Comp tool as the matte input, and is also outputted directly as the A Output Image.

The Back input image is sent to the Back input of the Comp tool node (an instance of the Blend & Comp tool). The Comp tool node provides a composite of the spill-suppressed front over the back, through the processed matte, both as a user convenience, and also as output on the Comp Output Image output.