Blender Cryptomatte: A Guide to Creating Object and Material Masks

What you’ll learn in this guide

Cryptomatte is a masking method that lets you isolate objects or materials in a render from the rest of the image, making them easier to edit later. With the Cryptomatte node in Blender’s Compositor, you can create a grayscale mask for selected elements or apply the mask to a color render. In architectural visualization, for example, this can be used to adjust furniture, a specific surface material, or plants in a scene without affecting other elements.

The steps cover enabling the necessary pass, rendering the scene, making selections in the Compositor, and using the output for the right purpose. The sources don’t specify a particular Blender version or account requirement, so check how the options appear in the version you’re using.

Requirements and preparation

You’ll need Blender, a scene to use in the Compositor, and a render. Cryptomatte data can be generated using Blender’s own render passes; you can also use data from other software that supports the standard. When using external data, you can select the Cryptomatte image within a multilayer OpenEXR as the source.

To create an object mask in Blender, enable the Cryptomatte Object pass in the View Layer’s Passes section, then render the scene. If you need a material or Asset mask, use the corresponding Cryptomatte type. The Asset option isolates groups of objects with the same parent; it’s not the same as Blender’s asset feature.

Render passes can be used as separate image layers in the Compositor. Cryptomatte can distinguish the contributions of multiple objects in a single pixel; according to the source guide, it also works with transparency, motion blur, and depth of field when using Cycles. If these features matter in your render, check the result with your engine and scene settings.

Creating a Cryptomatte mask

1. Choose a pass type. Enable the appropriate Cryptomatte pass for your selection: objects, materials, or groups with the same parent. If you only need to isolate objects, start with Cryptomatte Object.

2. Render the scene. Render after enabling the pass. When the Cryptomatte node’s source is set to Render, it can use the Cryptomatte passes from a specific View Layer.

3. Set up the nodes in the Compositor. Add a Cryptomatte node and a Viewer node. Connect the Render Layers node’s Image output to the Viewer node’s Image input. Use the selection button on the Cryptomatte node, then click the object you want to mask in the render shown in the Compositor backdrop. Repeat to select additional elements. If the image isn’t visible in the background, check whether Backdrop is enabled in the Compositor header.

4. Use the right output. If you only need a mask, use the Cryptomatte node’s Matte output, which provides a grayscale mask for the selected elements. To get a colored render of the selected elements with the rest of the image transparent, connect the Render Layers node’s Image output to the Cryptomatte node’s Image input, then use the node’s Image output. The Image input is required for the color image output; it can be left empty if you only need the Matte output.

5. Select multiple elements. You can enter object or material names manually in the Matte ID field. However, the guide shows selecting elements directly from the render using the plus and minus buttons next to the node as an easier approach. Expand the selection this way when you need to include multiple elements in the same mask.

6. Use Cryptomatte from a different source. If you have a Cryptomatte image from a multilayer OpenEXR file, change the node’s Source setting to Image and specify the image to use. The Render source option uses the View Layer passes from a particular scene. Keeping these two source options distinct helps ensure the mask is created from the expected data.

Common issues and limitations

If you can’t get a mask, first check that the relevant pass was enabled before rendering and that you’re using the correct View Layer. If the color render isn’t visible but the grayscale mask works, remember that the Cryptomatte node’s Image input may be empty: this input is needed for the color image the mask is applied to, not for the mask itself. If the render isn’t visible in the Compositor backdrop, check the Backdrop setting.

The Cryptomatte node doesn’t support metadata files known as sidecars and can’t be used inside a node group. Volume Objects are also unsupported. So if your scene contains volume objects, don’t assume they can be selected through Cryptomatte; the sources state that these objects aren’t supported.

Also, don’t treat Cryptomatte as the same workflow as the Object Index or Material Index pass. According to the source guide, Cryptomatte differs in that it supports multiple objects in a single pixel and handles transparency, motion blur, and depth of field in Cycles. The best pass depends on the selection you need and the render conditions.

Next steps in architecture and archviz workflows

When you need to change only the upholstery color of a sofa in an interior render, adjust a facade material, or apply a separate tone to a group of plants, isolating elements with masks can be useful without rendering again. The Matte output can be used in the Compositor to combine the selected area with other images or edits. The Image output isolates the selected object or material as it appears in the color render.

The next step is to compare the results of Object and Material selections in the same scene and choose the appropriate mask for the final image. Also check how the edges behave in a Cycles render with motion blur or depth of field. Since Cryptomatte passes are render data, selecting only the passes you need instead of enabling unnecessary ones—and testing the result for your scene—can make the workflow clearer.

Sources and license

This guide is adapted into Turkish from the Cryptomatte Node and Passes sections of the Blender Manual. Both sources are licensed under CC BY-SA 4.0.