ID Matte

Description
Many 3D programs tag each element in a scene with a unique Object ID. The ID Matte effect uses this information to create a matte that excludes everything in the scene except the element you want.

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

parameters
Aux. Channel Isolate elements based on Object ID or Material ID.


 * ID Selection :The ID value for an object.
 * To determine the ID of an object, select the ID type from the Aux. Channel menu in the Effect Controls panel, and click the object in the Composition panel or Layer panel using the Selection tool while the effect is selected. If Object ID is selected for Aux. Channel, ID Selection automatically updates to the Object ID for the object you click. 


 * Feather :The amount of feather along the edges of the matte.


 * Invert :Inverts the selection. Select to matte out the object specified by ID Selection. Deselect to matte out everything but the object (default).


 * Use Coverage :Creates a cleaner matte by removing the colors stored behind the object from the pixels along the edge of the matte. This option works only if the 3D image contains a coverage channel that stores information about the colors behind objects.

Reference

 * http://help.adobe.com/en_US/AfterEffects/9.0/WS3878526689cb91655866c1103a9d3c597-7bd3a.html