How to use Blender Cryptomatte: Object and material masks in renders

What you’ll learn in this guide

In Blender, Cryptomatte lets you isolate specific objects or materials in a render and use them as masks during compositing. This means you can work on the area containing a selected element instead of adjusting the entire image. Blender’s official manual describes Cryptomatte as an image standard used to create object and material masks; it also supports multiple objects within a single pixel.

These steps show you how to enable the required render pass, select an object with the Cryptomatte node in the Compositor, and use the mask. The same method can also be used to select materials. This guide is based on information in the current official Blender manuals.

Requirements

• You need Blender and a scene to render. The source manuals do not specify a particular Blender version number or account requirement.

• You must be able to enable the Cryptomatte pass in the View Layer settings.

• The Render Layers and Cryptomatte nodes are used to view the render and make a selection in the Compositor. The manual’s typical setup also includes a Viewer node.

• The objects or materials you want to select must be visible in the scene render; a Cryptomatte mask isolates elements in the rendered image.

Step by step: Create an object mask

1. Enable the Cryptomatte pass. In the Properties editor, go to the View Layer tab, then to the Passes section. Enable the Object pass from the Cryptomatte options and render the scene. The manual describes Object for isolating objects, Material for isolating materials, and Asset for isolating groups of objects that share the same parent. The Asset option is unrelated to Blender’s asset feature.

2. Set up the nodes in the Compositor. Add a Cryptomatte node and a Viewer node. Connect the Image output of the Render Layers node to the Image input of the Viewer node. This lets you see the render in the Compositor backdrop and helps you identify the element to select. If the image is not visible, check whether Backdrop is enabled in the Compositor header, as the manual recommends.

3. Select the object to mask. Use the picker button on the Cryptomatte node and click the object you want to include in the image. Repeat the selection if you need multiple objects. You can also type object names into the Matte ID field; the manual notes that using the plus and minus buttons next to it is easier.

4. Get and use the mask. The Matte output of the Cryptomatte node provides a grayscale mask of the selected objects. You can use this output as a mask in subsequent compositing operations. The node’s Image output provides the color render connected to the Image input, with areas outside the selected elements made transparent. The Image input does not need to be connected if you only need the grayscale mask; to use the Image output, however, an image must be connected to that input.

5. Change the image source if needed. When the Cryptomatte node’s source is set to Render, it uses the Cryptomatte passes from a specific View Layer. The Image option can use Cryptomatte data from a multilayer OpenEXR file. When you select Image as the source, choose the relevant image and layer. Select the source and layer based on where your render data is stored.

6. Check the result. The Pick output on the node provides Cryptomatte’s color-coded display, which you can use to select elements. Check the mask in the Matte output to confirm that the correct area is selected. It’s important to review the rendered result if you also need to isolate overlapping elements or transparent edges. The manual states that Cryptomatte supports motion blur and depth of field when using Cycles.

Common mistakes and limitations

Adding the node without enabling the pass: The Cryptomatte node generates a mask from Cryptomatte data. When working with a Blender render, you must first enable the relevant pass under View Layer > Passes and render the scene. The node’s Render source uses Cryptomatte passes from a specific View Layer.

Not checking Backdrop: If the render is not visible in the Compositor backdrop, making a selection can be difficult. Check the Viewer connection and the Backdrop option. This step is for viewing the image in the node backdrop; you can use the Cryptomatte node’s Matte output for the mask itself.

Using the wrong output: Matte provides a standalone grayscale mask. The Image output applies the mask to the render connected to the Image input and makes areas outside the selection transparent. If you are not getting the expected result, check that you are using the right output and that an image is connected to the Image input when using the Image output.

Expecting unsupported content to work: According to the official manual, Cryptomatte sidecar files are not supported; the Cryptomatte node cannot be used inside a node group, and Volume Objects are not supported. Keep these limitations in mind when planning your compositing setup.

Impact on architecture and visualization workflows

In architectural interior and exterior visualization, Cryptomatte can help visualization teams isolate a specific piece of furniture, surface, or scene element with a mask after rendering. For example, you can make a compositing adjustment to a selected material or object; using a mask lets you focus on the target element instead of working on the entire render. This is a workflow application of the masking function described in the source materials.

First, confirm that the pass is included in the render and that the required element can be selected in the scene. How Cryptomatte data and the render are stored together is especially important when using a multilayer OpenEXR source. The source materials do not specify hardware requirements, licensing terms, or version compatibility, so you should also check the Blender version used in your project and your organization’s file-delivery workflow. Cryptomatte passes add data; the source warns about memory and render time for denoising data, but does not specify a separate performance cost for Cryptomatte.

Next steps

Once you are comfortable with the object-mask workflow, try the same approach with the Material pass to isolate materials. If you need to isolate a group of objects, remember that the Asset option is described as covering objects with the same parent. Check the results with different scene and material setups; in areas with transparency or overlap in particular, verify that the mask works as expected alongside the image.

Sources and license

This tutorial is adapted into English from the “Passes” and “Cryptomatte Node” guides in the Blender Manual. Both sources are licensed under CC BY-SA 4.0.