Cryptomatte

 

Arnold supports Cryptomatte, an ID matte creation tool created by Jonah Friedman. It creates ID mattes automatically with support for motion blur, transparency, and depth of field. Names, object namespaces, and material names can be used to organize ID mattes in the scene.

The following Cryptomatte AOVs are available under AOVs.

• crypto_asset creates the same matte for all assets.
• crypto_material creates a matte based on the assigned shader.
• crypto_object creates a matte based on the object name.

 

The steps are:

1. Create the Cryptomatte material and assign it to an arnoldAov shader slot.
2. Set the Cryptomatte material on an ArnoldGlobalSettings node, in Channel Definitions -> aov_shaders (add an entry and assign your Cryptomatte material).
3. Create ArnoldOutputChannelDefine and RenderOutputDefine nodes for each of the Cryptomatte channels you care about: probably some of crypto_object, crypto_material and crypto_asset.
   1. Make sure to leave the type set to RGBA.
   2. Don't forget to set the channel on RenderOutputDefine to your channel created in ArnoldOutputChannelDefine.