You can create a crop box to limit the area where the key setup is applied.

Using a crop box as you create the key speeds up interactivity, which is especially useful when working at high resolutions. You can also process the composite with a crop box. By setting the crop box to surround just the foreground subject, you can save processing time. Everything outside the crop box will be processed as black on the matte.

The crop box is applied to the Front and Matte branches, but not to the Back branch. With the exception of the GMask node, you can see the crop box as you work in different nodes. When you open the Garbage Mask module, you no longer see a defined crop box. However, once you return to the Modular Keyer, you see the crop box, and can use it as before, regardless of any defined garbage masks.

To use the crop box:

1. Press Esc to display the image window.
2. Click Setup.

   The Setup menu appears.

   
   

3. Enable Crop.
4. Click Draw.
5. Draw the crop box on the image by selecting a point on the image and dragging the cursor diagonally. Drag the crop box handles to adjust the size and aspect ratio of the box.
   NoteAs an alternative to using the Draw button, you can press Shift+Alt and draw the crop box. The advantage of using this hotkey is that you can redraw the crop box when any other menu is displayed. The Crop button must be enabled to use either of these methods.
6. You can now go into any node menu and create the key. You will only see the results of your changes within the crop box.
7. If you want to remove the crop box when you have finished creating the key, go back to the Setup menu and disable the Crop button.

   If you want to process the clip with the crop box, simply leave the Crop button enabled when you process.