A very simple keyer with a big variety of different operations inspired by Nukes most simple Keyer-node.
img = Connect the image you want to key from
Connect an image and choose the operation you want to use to create your key. You can adjust white- and black-point as needed to key the you want. You can also enable range-controls for added functionality.
Simply put, this tool copies channels (from different colourspaces or other operations) into the alpha channel, a following Grade-node helps with adjusting the levels. The red-, green- and bluescreen operations are the most simple colour-difference setups. The range-control is build with a 2nd yet inverted Grade-node, the difference between the two is the resulting range.