Use the 2D histogram node to display the luminance of the matte. You can add this node to any part of the pipeline except the Front pipe of the CBlend node.

To display the matte with the 2D histogram:

1. Select Move from the Edit Mode box.

   
   

2. Select the 2D histogram node.

   The histogram appears.

3. Press Esc to view the image.

   The histogram is identical to the histogram in the traditional Keyer. See Adjusting the Luminance of the Key.