How to Use Cryptomatte Passes in Blender

This guide provides a comprehensive overview of Cryptomatte passes in 3D computer graphics and delivers a step-by-step walkthrough for generating and using them in Blender. You will learn what makes Cryptomatte superior to traditional masking techniques, how to configure render passes in the Cycles engine, and how to isolate specific objects or materials in Blender's Compositor.

What Is a Cryptomatte Pass?

Cryptomatte is an open-source standard created by Psyop that automatically generates ID mattes during rendering. Unlike traditional RGB masks or ID passes ("clown passes"), Cryptomatte natively supports:

  • Motion blur
  • Depth of field
  • Transparency and glass
  • Hair and soft particle edges

Traditional ID passes often suffer from edge fringing because anti-aliasing mixes pixel colors, making it impossible to pull clean keys. Cryptomatte solves this by encoding object names, material names, and coverage percentages directly into a multi-channel OpenEXR file without sacrificing edge quality.

How to Enable Cryptomatte in Blender

Blender supports Cryptomatte natively in the Cycles render engine. Follow these steps to enable it:

  1. Set Render Engine to Cycles:
    • Go to the Render Properties tab (camera icon) in the Properties panel.
    • Ensure your render engine is set to Cycles.
  2. Enable Cryptomatte Passes:
    • Navigate to the View Layer Properties tab.
    • Scroll down to the Passes panel and expand the Cryptomatte sub-panel.
    • Check the boxes for the types of mattes you require:
      • Object: Generates mattes based on individual mesh objects.
      • Material: Generates mattes based on assigned materials.
      • Asset: Generates mattes based on grouped asset hierarchies or parent-child groupings.
  3. Adjust Cryptomatte Levels:
    • In the same panel, set the Levels value (default is 6). This defines the maximum number of overlapping objects a single pixel can store. A value of 6 is generally sufficient for most production scenes.
  4. Set Up Export Format (For External Compositing):
    • If compositing in software like Nuke, After Effects, or DaVinci Resolve, switch to the Output Properties tab.
    • Set File Format to OpenEXR MultiLayer.
    • Set Color Depth to Float (Full) or Float (Half) to ensure the ID hashes are preserved accurately.

How to Composite Cryptomatte in Blender

Once rendered, you can isolate scene elements directly inside Blender's built-in Compositor:

  1. Switch to the Compositing workspace and check the Use Nodes box.
  2. Press Shift + A and search for the Cryptomatte node.
  3. Connect the Image output from the Render Layers node to the Image input of the Cryptomatte node.
  4. Add a Viewer node (Shift + A > Output > Viewer) and connect the Image output of the Cryptomatte node to it.
  5. In the Cryptomatte node:
    • Select the layer type (CryptoObject, CryptoMaterial, or CryptoAsset) using the dropdown menu.
    • Click the Add (+) eyedropper tool.
    • Click on any object or material in the backdrop or Image Editor to add it to the matte selection.
  6. Use the Matte output of the Cryptomatte node as a factor input for color grading nodes, such as Color Balance, Hue Saturation Value, or Mix Color.