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Reducing Cycles Noise for Backgrounds

Published July 30, 2013 by Moby

I have been working on a way to remove cycles noise, in particular for backgrounds and foregrounds. I find the parts of the scene which are not the focus are often much noisier than the focus. As a demonstration, in the following example I have applied this method to the ground. Watch in full screen and in HD to make the difference more obvious:



Here is a still from that video:


My method avoids the smudgy look that is often a side effect of bilateral blur:



The way this works is that it is a selective motion blur that doesn’t blur the detail in the scene (here the water). This is done by doing a separate render, in BI with no lighting and a pure white background. This is what a frame from that scene will look like:

White will denote areas to be blurred and black areas to preserve. 

The following is a simplification of my compositor setup. It will apply 1 frame of blur to your scene. To increase the level of noise reduction, you will duplicate the selected nodes (apart from the compositor output) and “mix” them together. My example video used 12 duplicates. 

You will then change the “offset” values for each duplicate by 1, so that each pair of render + black and white blender internal render has a unique offset value. The unselected node is what will provide the detail to your scene, so set it’s offset value equal to the highest one in the scene.


That should explain it. Do not hesitate to ask for clarification on anything that is unclear! 

Thanks for reading

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  • This is interesting. Unfortunately, the poor compression by Youtube really obscures the results that you are trying to show, it's hard to see the differences between the before/after properly.

    I'm unsure why this technique is better than just rendering 2 render layers, and then slightly blurring the background layer? Could you go into more detail? Thanks!

  • I hope you'll get all updates you're looking for Smile