This tutorial shows how to create Z Depth, dust, and Object Position masks that can be used in a compositing package to layer shading effects such as depth of field, dirt, dust, or snow. They use a combination of Arnold shaders such as Utility, Range, and State Float. Thanks to Slava Sych for the assistance with this tutorial.

A scene file can be found here.

Depth Mask

• Create a State Float shader. Set the Variable parameter to Ray Length (Rl).

• Create a Range shader and connect the State Float shader Output to the Input of the Range shader. Change the following parameters of the Range shader:

• • Input Min: 0.6 (this value depends on the distance from the camera your object is).
• • Output Max: 1.5 (this value depends on the distance from the camera your object is).
• • Smoothstep : Enabled

Object Position (n) Dust Mask

• Create a Utility shader. Set the following parameters for the Utility shader:

• • Color Mode: Normal (n)
• • Shade Mode: Flat

• Create a Range shader and connect the Utility shaders Output G to the Input of the Range shader. Enable Smoothstep and control the mask position with the Input Min/Max parameters.

Object Position (P) Mask

• Create a Utility shader. Set the following parameters for the Utility shader:

• • Color Mode: Shading Point (P)
• • Shade Mode: Flat

• Create a Range shader and connect the Utility shaders Output G to the Input of the Range shader. Enable Smoothstep and control the mask position with the Input Min/max parameters.

If you cannot connect a single out color (Out G) to an Input in your DCC, use a RGBA to Float (mode G) shader to convert it.