.. _bpy.types.CompositorNodeChannelMatte:

****************
Channel Key Node
****************

.. figure:: /images/compositing_node-types_CompositorNodeChannelMatte.png
   :align: right

   Channel Key Node.

The *Channel Key* node determines background objects from foreground objects by
the difference in the selected channel's levels.

For example in YUV color space,
this is useful when compositing stock footage of explosions (very bright)
which are normally shot against a solid, dark background.


Inputs
======

Image
   Standard image input.


Properties
==========

Color Space
   This button selects what color space the channels will represent.

   RGB, HSV, YUV, YCbCr
Channel
   This button selects the channel, defined by the Color Space, to use to determine the matte.
Algorithm
   Max., Single
Limit
   It is possible to have a separation between the two values to allow for a gradient of
   transparency between foreground and background objects.

   High
      Determines the lowest values that are considered foreground.
      (Which is supposed to be -- relatively -- height values: from this value to 1.0.)
   Low
      Determines the highest values that are considered to be background objects.
      (Which is supposed to be -- relatively -- low values: from 0.0 to this value.)


Outputs
=======

Image
   Image with an alpha channel adjusted for the keyed selection.
Matte
   A black-and-white alpha mask of the key.