How to keep noise around lights

I find the noise in that picture really nice, is there a way in blender to keep the noise around lights and only denoise the space between the lights?

brain5.blend (2.4 MB)

You could do it as a layered render, rendering out the volumetrics separately from the synapses.

My steps:

  1. Separate the main object from clutter and hide the clutter.
  2. Duplicate the material for the main object and give it a material ID.
  3. Zoom into ligthsource. Edit mesh and assign new material to area around lightsource.
  4. Repeat point 3 for all light sources - you don’t have that many.
  5. Activate material ID in passes. I guess you see where this is going by now.
  6. Activate denoise and render.
  7. In comp pass IndexMA through ID mask, some blur and dilate/erode nodes, possibly a color ramp.
  8. Use the above to mix between image and noisy image. Below I added additional value just to clarify what’s going on.
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Thanks for the detailed explain, i try it out.
Didnt have used passes yet, i dig in.

Thanks, it works. First i was wondering why a IndexMA is needed, but it is for masking.
I just wonder why there are layers for all kinds of light, and it seems none can be easily used as a mask for that to replace IndexMA.
There isnt a layer just for light sources with position, area and color!?

How does that work with a torus light, monkey light, or any other emission based geometry lights?
You might be able to create a mask by filtering colors in your image. I don’t like this method if I can avoid it - what if you add something blue later?

Since analytical lights can’t be seen by camera, you’d have to setup a refractive sphere around your camera, base in on incoming normal and give it some roughness - just to make it show up for the “camera”. And then render out in isolation for a mask image - I don’t know, doable, but kind of weird.