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I have a cryptomatte pass that refuses to work in Nuke. I'd like to use the Blender compositor to render out a series of mattes from the crypto matte layer of my .exr sequence. The crypto matte works in the blender compositor. Here's the thing. (Forgive me if this is something stupidly simple) I have the cryptomatte image sequence in a new composite tree in a new blender scene. I have it all set up to make the mattes I need. All I need to do is render out the results of the composite tree out of blender. How do I do that?

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You can use File Output nodes in the compositor to output whatever you want from Compositor nodes.

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If you render everything to Multilayer EXR format, Cryptomatte layers are saved. They obviously need to be enabled in the View Layer properties:

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Some software might recognise them, like for example there is this addon for Photoshop, although Photoshop is probably a bad example for compositing as it's very limited for this purpose.

Keep in mind, you should do compositing in linear color space, preferably 32bit float format.

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  • $\begingroup$ There's no render button on the file output node that I can see. How do I start the rendering process for the compositor? $\endgroup$
    – MattL
    Jan 25, 2023 at 18:28
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    $\begingroup$ Compositor does not have separate way of rendering. It is processed during normal render. If you do not need your 3d scene rendered, you need to disable or delete Render Layers node - this way you can render only compositing if you work with loaded image sequences. $\endgroup$ Jan 25, 2023 at 18:35
  • $\begingroup$ So do I need to render the 3d scene to get the compositor to write out it's image sequence? I already have the cryptomattes rendered. I really don't want to render the 3D scene again ( very long render) $\endgroup$
    – MattL
    Jan 25, 2023 at 18:36
  • $\begingroup$ Ok thanks. This is what I needed. $\endgroup$
    – MattL
    Jan 25, 2023 at 18:40
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    $\begingroup$ You can make a new file with empty scene and delete the Render Layers node from the compositor. Load the Multilayer EXR image sequence as regular image(there is Detect Sequences option in the n panel of open file dialog), process them as you want, setup File Output nodes and simply render. $\endgroup$ Jan 25, 2023 at 18:40

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