For Maya software and mental ray for Maya.

To increase or decrease the mask value for an object

1. In the Matte Opacity section of an object’s material Attribute Editor, set Matte OpacityMode to Opacity Gain and adjust the Matte Opacity value.

   During rendering, Maya first generates the mask channel, then multiplies the mask values for the object by the Matte Opacity value. For example, if Matte Opacity is 1, the mask values for the object remains unchanged; if Matte Opacity is 0.5, the mask values for the object are half their original values.

To set the mask value for an object to a constant value

1. In the Matte Opacity section of an object’s material Attribute Editor, set Matte OpacityMode to Solid Matte and adjust the Matte Opacity value.

   If the object is transparent, any objects behind it appear in the mask channel.

   During rendering, Maya first generates the mask channel, then sets the mask values for the object to the Matte Opacity value. For example, if Matte Opacity is 1, the mask values for the object are 1; if Matte Opacity is 0.5, the mask values for the object are 0.5.

To set the mask value for an object to zero

1. In the Matte Opacity section of an object’s materials Attribute Editor, set Matte Opacity Mode to Black Hole.

   During rendering, Maya first generates the mask channel, then sets the mask values for the object to 0. If the object is transparent, any objects behind it will not appear in the mask channel.