TIP: Using a CustomAOV instead of ObjectMask with multi-instance cloning

[peter.fagerberg]

Hi there! I thought I'd share a little quicktip for those times when you have multi-instancing objects in your scene, need a quick selective matte for compositing, and don't really want to mess around with crypto mattes, etc.

Arnold's Object Mask is fast and easy to use but it doesn't seem to play well with MoGraph cloning in multi-instance mode or Arnold Scatter (which I guess is always in multi-instance mode). If you throw an Object Mask on the top level of your object hierarchy, you'll get "holes" for all multi-instancing objects. You can put separate Object Masks on your Scatter objects, and then merge them in post, but if you're using MoGraph Cloning in multi-instance mode, Arnold's Object Mask won't work at all.

👉But there's a very quick workaround to mask all your geometry: create a flat white material, add an Arnold Custom AOV to the top object, give it a name, add the material to the AOV and Bob's your uncle!

Let me know if you have an even easier way of doing it!

[peter_horvath]

Thank you very much for adding this tip, it's very useful!

Btw, I was doing some changes around the object mask tag and noticed this misbehavior with Multi-Instances. It is going to be fixed in the next release, that means adding the object mask tag to the Cloner or parent Null will properly mask out all instances.

[peter.fagerberg]

Excellent, Peter — that fix will make the Object Mask tag much more helpful! And as always, the Arnold team is way ahead of me! 😃