Blender Cryptomatte Guide: Create Object and Material Masks in Renders

What you’ll learn in this guide

Cryptomatte lets you select specific objects or materials in a render and create masks for them. In Blender, you can use these masks in the Compositor to color selected areas, isolate them from the image, or pass them to another editing step. The steps here cover preparing the render pass, selecting items in the Cryptomatte node, and using the mask output.

This workflow is particularly useful in interior visualization for handling furniture, walls, floors, or material groups independently from the rest of the image. The key point is that Cryptomatte is not a new render engine; it’s a Compositor tool that creates masks from render data.

Requirements

You’ll need Blender and a scene you can use in the Compositor. The source guides do not specify a particular Blender version or account requirements. The steps below therefore assume a Blender installation with Cryptomatte and the relevant render passes available in the interface.

• Prepare a scene containing the objects or materials you want to isolate in the render.

• You can use Cycles or EEVEE as the render engine; Cryptomatte pass types are available in relation to the engine.

• You’ll need access to View Layer properties and the Compositor to enable render passes and connect nodes.

• If you’re working with a pre-rendered image, it must be a multilayer OpenEXR. Cryptomatte metadata sidecar files are not supported.

Step-by-step: Create a Cryptomatte mask

1. Choose what you want to isolate

First, decide whether the mask should apply to an object, a material, or a group that shares the same parent. Use the Object pass to select objects individually, the Material pass to select a particular surface material, or the Asset option to target groups of objects linked to the same parent; this is unrelated to Blender’s asset feature.

This choice determines which Cryptomatte layer to use in the next Compositor step. For example, in an interior render, Material may be the better option for masking different surfaces that use the same material, while Object may be more suitable for isolating a single chair.

2. Enable the Cryptomatte render pass

In Properties, open the Passes panel under View Layer. Under the Cryptomatte heading, enable the Object, Material, or Asset type you need. Then render the scene. When the Render source is selected, the Cryptomatte node can use the relevant View Layer passes.

The Levels setting determines the maximum number of items that can be distinguished in each pixel. The number of Cryptomatte images shown in the Render Layers node is half this level; each image can reference two items in a pixel. Keep in mind that each image can carry two items when considering the number of layers you need.

3. Add a Cryptomatte node in the Compositor

Create a Cryptomatte node in the Compositor and set its source to Render. This source uses the scene and View Layer information. If you’re working from a previously rendered multilayer OpenEXR, choose Image as the source and select the image to use. Check that the Cryptomatte layer matches the target View Layer and the Object, Material, or Asset type.

Adding a Viewer node makes it easier to view the image in the Compositor backdrop. Connect the Image output of the Render Layers node to the Viewer. If the image isn’t visible in the backdrop, make sure the Backdrop option in the Compositor header is enabled.

4. Select the items to include in the mask

Use the selection button in the Cryptomatte node and click the target object in the Compositor backdrop. Repeat to select more than one item. The names of selected items appear in the Matte ID field; adding them with the selection buttons is easier than typing their names manually.

Once you’ve finished selecting, the Matte output provides a grayscale mask of the selected objects or materials. The Image output provides the image with the mask applied: selected items remain visible while the rest of the image becomes transparent. If you only need the mask, you can leave the Cryptomatte node’s Image input unconnected; this input is required for the Image output to work.

5. Use the mask in the Compositor workflow

Use the Matte output as a mask for subsequent Compositor operations. If you also want to use the color render along with the mask, connect the Render Layers Image output to the Cryptomatte node’s Image input, then pass the node’s Image output to the next operation. This lets you use the selection as a layer isolated from the rest of the image.

With Cycles, Cryptomatte supports transparency, motion blur, and depth of field in the image. In EEVEE, depth of field and motion blur are not rendered in passes other than Combined; these effects can be simulated separately in the Compositor. This difference can affect how blurred edges and focus effects appear in the mask in the final image.

Common mistakes and limitations

• Choosing the wrong layer: The Cryptomatte layer must match both the correct View Layer and the correct type. Selecting a Material layer when you want to isolate an object may not produce the expected mask.

• Mistaking the Image output for a mask: Matte is a grayscale mask; Image is a masked color image in which the selected items remain visible.

• Expecting a color output when the Image input isn’t connected: This input can be left unconnected for a grayscale mask. For a masked color Image output, connect the render image to the Image input.

• Rendering without enabling the pass: When using the Render source, you must enable the required Cryptomatte pass under View Layer Passes.

• Using unsupported data: Volume objects are not supported, and metadata sidecar files cannot be used. The Cryptomatte node also cannot be used inside a node group.

Next steps: Architecture and visualization workflows

In architectural and interior visualization, Cryptomatte can be used for targeted edits such as changing the tone of a material or handling a particular piece of furniture separately in a composition. This approach relies on extracting the relevant object or material mask from the render data; however, changes to lighting or geometry may require you to work in the source scene.

Before using this method in an office, it’s useful to test the render engine, pass settings, and intended output type. In particular, keep in mind EEVEE’s limitations for depth of field and motion blur in passes other than Combined, and that denoising passes in Cycles can increase memory use and render time. The sources do not specify hardware or licensing requirements for Cryptomatte.

Sources and license

This tutorial is adapted from the “Cryptomatte Node” and “Passes” guides in the Blender Manual. Both sources are published under the CC BY-SA 4.0 license; the content has been adapted into Turkish based on these sources.