When you key an image or an image sequence, you can use a keyer or a collection of keying tools to generate a matte or remove color spill from a shot. You may also need to generate more than one key to achieve the desired result.

To access the Keying tools:

1. Press the tilde key (~) or middle-click to display the Gate UI.
2. Swipe through the east gate to display the Tools tab.
   
3. Expand the Keying tool folder to access the Keying tools.

   The Keying tools include Color Curves, Diamond Keyer, the Difference tool, and Luma Keyer.

To add a keying tool to the process tree:

1. From the Tools tab, drag a keying tool to the process tree in Schematic.
2. Drag the Keying tool over the output of a node that you wish to key. When the connection is highlighted, release the mouse.

   The keyer tool is added to the process tree.