---
title: "V-Ray Cryptomatte"
canonical: "https://documentation.chaos.com/space/VRAYHOUDINI/113281126/V-Ray%20Cryptomatte"
format: markdown
---
This page gives information on the Cryptomatte Render Element.


## **Overview**

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## **Parameters**

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> ℹ️ When in **Per Attribute Value** mode, the Cryptomatte element supports **Packed Primitives** or **Packed Alembic Primitives** only. Attributes placed on the individual face of a live polygon geometry are **not** supported. The attribute should be of type **string**, and placed on the **primitives** of the rendered **packed** geometry.
> ℹ️ 
> ℹ️ E.g. you could specify **path** under **Attribute Name** for a **Delayed Load Alembic** file to generate matte IDs based on the **partitioning** of the Alembic file.

> ℹ️ When in **Proxy Sub-Object** mode, **instanced** V-Ray Proxies share the **same internal matte ID**, producing the same mask for the same sub-object of every instance. The recommended workflow in this case is to use a separate Cryptomatte render element set in **Per Attribute Value **mode, with a custom **primitive, string attribute** placed on the instanced V-Ray Proxies to generate a unique per-instance matte ID, then mask the instances in compositing.



## **Common Use**

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After producing a multichannel exr image with the Cryptomatte layer, we can use it in a compositing application, such as Nuke, to color correct the image. This example shows the before and after color correcting.




## **Notes**

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- When the Save Deep Data to Separate Files option is enabled from V-Ray Renderer ROP > Images tab > Advanced settings rollout and the output is OpenEXR, you can choose to save the Cryptomatte channels as a separate EXR file. The option is available for both V-Ray CPU and V-Ray GPU rendering. Read more at [Images Tab](https://docs-chaos.atlassian.net/wiki/spaces/VRAYHOUDINI/pages/113279153).


## **References**

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- [Cryptomatte GitHub](https://github.com/Psyop/Cryptomatte)