To reduce render times I want to apply some noise reduction on a simple scene using Cycles.

I don't want to apply it to all scene because it blurs a bit the first plane (A), so my idea is to separate layers and apply the denoise in the background layers, where the shadows are falling (B) and composite them.

enter image description here

How can I apply denoise to only one layer?

  • 1
    $\begingroup$ I don't know enough about denoising in Blender to post an answer, but I think the denoising operation is performed on the resultant image after rendering, so it would not be possible to denoise a single layer. If anyone knows better I wouldn't mind being proven wrong. $\endgroup$
    – Paul O.
    Sep 17, 2018 at 12:55
  • $\begingroup$ One option, of course, is to simply render the background layers first and then composite them, but I want to explore the layers first. :o) $\endgroup$
    – Rafael
    Sep 17, 2018 at 12:57
  • $\begingroup$ Denoising (if you mean built in function of Blender called that way) can't work separately on different layers, but you can perform de noising operation on separate layers in old fashion way, using nodes in Compositor. $\endgroup$
    – Mzidare
    Sep 17, 2018 at 15:33

1 Answer 1


I have listed down the steps and attached the implemented blender file here.

  1. Move the red circular object to layer 2
  2. Give a material index to red object. I have given it a value of 1. We do this to have a mask for this object, which will be helpful during compositing.

enter image description here

3.Setup render layers as follows. Notice denoising is checked in render layer with shadow. Also 'material index' pass is checked for red object layer, which we will use in compositing.

enter image description here

enter image description here

  1. In the compositor, set up the nodes as shown below.Basically, the material Id mask cuts out just the red object from the second render layer. We then add this to the other render layer with shadow.

enter image description here

Done! Checkout the attached blend file, where I implemented the above steps.

  • $\begingroup$ Oh. Let me take a look to understand it, and if the case mark this as solved :o) $\endgroup$
    – Rafael
    Sep 17, 2018 at 19:51
  • $\begingroup$ Sure! Let me know if you need any more clarification. $\endgroup$
    – Teja
    Sep 17, 2018 at 20:15
  • $\begingroup$ Please mark the answer as accepted ✅. That way, it wont show up in the unanswered section. $\endgroup$
    – Teja
    Sep 19, 2018 at 3:47
  • $\begingroup$ I'm still testing this. I will not forget to mark it. Promised. $\endgroup$
    – Rafael
    Sep 19, 2018 at 5:49

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