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After importing a 3D scene from SweetHome3d (in .obj format), my preview window and also the F12 rendering result suddenly has very much "noise". (Please tell me if that's the correct term, I'm a blender newbie)

I never saw this when working on small scenes that I created from scratch or any tutorial files. As I added 3 point light sources to the room to rule out noise due to a too dark room, I assume it has something to do with the size of the scene? Any idea how to improve the results?

This is a screenshot, you can see the problem in the upper left window: enter image description here

And this is how the final result looks like:

enter image description here

A screenshot of light path and samples settings:

enter image description here

lathspell
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    You need more samples: read: - Render Samples set too low –  Jul 15 '16 at 20:46
  • Are you aware that you are using Cycles render engine and not Blender Internal? (I ask because you said you feel a bit blender newby) – Carlo Jul 15 '16 at 21:17
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    @Carlo: Well, I read that Cycles is better and some plugins like the "online materials library" do not work with BI. Did I get this wrong? Is BI still preferred? – lathspell Jul 15 '16 at 21:21
  • No, I didn't mean to say you should change render engine (the choiche depends on your need). Just saying that as Cycles is an unbiased render engine, a bit of noise should be expected. And I felt like you were surprised by seeing it, so I asked if you were aware of not using BI (wich is instead biased) – Carlo Jul 15 '16 at 21:28
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    BTW, giving a closer look at your images, that seems not usual "noise" but more "lots of fireflies". Do you have many mirroring surfaces/very strong light sources/glass shaders? Could you show your light path and samples panels? – Carlo Jul 15 '16 at 21:37
  • @Carlo: I've uploaded a new screenshot with those settings. Meanwhile I'll google what fireflys are :-) – lathspell Jul 15 '16 at 21:44
  • Give also a look here: https://www.blenderguru.com/articles/7-ways-get-rid-fireflies/ – Carlo Jul 15 '16 at 21:45
  • None of those tips solved the problem. Using all of them made the F12 rendering at least look "acceptable". The preview is still noisy though. Maybe the imported materials have indeed some kind of "default texture" which totally confuses the rendering engine. I'll try to replace floor, ceiling and walls with a simple white diffuse shader. – lathspell Jul 15 '16 at 21:57
  • If the problem still persist, consider the option to uplad your file (or a simplified version of it) on http://blend-exchange.giantcowfilms.com/. With a more in-depth look of the scene I'm sure someone will find out the source of the noise – Carlo Jul 15 '16 at 22:06
  • Indoor scenes cause tons of noise because the light bounces off all the walls and stuff. Have you tried using portals? See https://www.blenderguru.com/tutorials/using-portals-accelerate-render-times/ – Anson Savage Jul 15 '16 at 22:13
  • The video looked promising but I did not notice any effect on my scene. After much trial and error I found some settings I can live with, all in the Camera settings:
    1. render/device=GPU (although it sometimes crash Blender)
    2. sampling: "branched path tracing" instead of "path tracing"
    3. sampling: AA Samples increase as much as I am willing to wait (64 looks ok)
     – lathspell Jul 16 '16 at 01:01

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