How to Eliminate Sampling Noise

How to Eliminate Sampling Noise in the 3Delight RSL renderer

Under-sampling is almost always the cause of noise in your renders.

When noise is present in your image the following step-by-step guide should help you locate it and resolve it.

Let's first look at where are the samples settings in the various UIs in Maya: 

RenderPass	Light	Material	Fluids	OpenVDB
The global sampling settings are in the Render Pass, where you can find: Quality > Pixel Samples: 3x3 This means 3x3=9 samples taken within each pixel. Pixel Samples is the main quality/performance parameter in 3Delight: its total value will act as a floor for ALL sampling parameters, meaning if you use a pixel samples value of 8x8 (64), all other sampling parameters (such as the ones below) even when set to a lower value will use 64 samples.  Quality > Area Light Samples: 16  Indirect Illumination > Samples: 64 Note that unlike other renderers 3Delight offers a high quality "Sinc 4, 4" filter which is set by default and is suggested for high quality renders.	On Lights (light shaders). There are two types of Lights: 1. (geometric) Area lights, the latter are sampled globally from the RenderPass via Quality> Area Light Samples (see previous). This affects both direct illumination and shadowing.  2. Delta lights (lights with no area): they are sampled locally. In Maya there are 3 types of delta lights: directional, point and spot. Delta lights have no actual area but can produce soft shadows via increasing the Maya "Light Radius" attribute, you can control its sampling by tweaking the number of shadow rays in the Raytrace Shadow section of the Maya attribute editor.	On Materials (surface shaders). As en example in the UI screenshot above you can see the sampling settings in the 3DelightMaterial, if you are using custom materials you will have other sampling settings depending on the material design. In general consider that each indirect specular and subsurface component usually requires a sample setting.	On Volumes (volume shaders). This is for Maya Fluids containers.	On Volumes (volume shaders). This is for OpenVDB shape.

Now let's go into the steps to check and eliminate noise:

1. Always first render your image with the default 3Delight sampling settings in renderPass, lights, shaders and volumes. Ideally you should render the main shading components Image Layers / AOVs to identify which is the exact source of noises (see the 'tips' below).
   
   

2. The very first question to ask yourself: do you require 3D motion blur and/or 3D depth of field (DOF)? If so enable them and render with default settings. Then is there any noise due to motion blur and/or DOF? (tip: looking at the alpha channel will easily tell you if more pixel sampling is needed)
   
   → First make sure you turn on Motion Blur and/or Depth of Field in the quality group of attributes of the Render Settings. Note that for DOF you also need to enable DOF in the Maya camera shape node. You will most likely need to increase the pixel samples (in Quality: Sampling) from the default value (3x3) to a higher value. Typical values for motion blurred and/or DOF shots can be in the range of 6x6 to 12x12 or even more when DOF is narrow (high blur). By increasing pixel samples you will also automatically resolve any edge aliasing you might experience.
   
   

   Note that 3Delight is designed for production usage and, unlike other rendering engines, its efficient sampling allows for high pixel samples counts without exponential increase in render times. Therefore we strongly recommend to render with 3D motion blur and DOF rather than offsetting these important aspects of imagery to the compositing phase where equivalent quality cannot be achieved and where the compositing graph would result overcomplicated and time consuming. The decision whether to render with 3D motion blur and/or DOF should be clear upfront then. This guide assumes you are aware of it and optimize sampling based on an ad-hoc pixel samples count which optimally renders such effects. This guide also naturally assumes you are rendering with the default Path Tracing engine.

3. Do you still see Indirect Diffuse Illumination noise? (tip: verify in the respective Indirect Illumination image layers)
   
   → You can then increase the Samples attributes (default is 64) in the Quality: Indirect Illumination of the Render Settings. 
    
4. Do you still see noise in the direct diffuse illumination and shadowing produced by area lights? (tip: verify this, respectively, in the direct diffuse image layer and,optionally, in the auxiliary aov_shadow image layer)
   
   → You can then increase the Area Light Samples attributes (default is 16) in the Quality: Sampling of the Render Settings.
    
5. Do you still see reflection and/or refraction noise? Not that reflections of area lights counts as a reflection effect! (tip: verify this in the respective reflections/refractions image layers)
   
   → You can then increase the Samples specified locally for Reflection and/or Refraction of the material shaders of each objects exhibiting such noise (such as in the 3Delight Material). Note that in 3Delight samples are considered to be a maximum number of  samples to use, therefore higher value might be input. Indirect specular samples for 3Delight materials is 32 by default.
    
6. Do you have any ray-traced subsurface scattering and still see subsurface noise? (tip: verify this in the respective subsurface image layer)
   
   → You can then increase local subsurface samples on your materials, of the standard materials distributed with 3Delight for Maya both 3DelightMaterial  and 3DelightSkin have a local subsurface samples control.
   
   
7. Do you have any volumes (e.g fluids, volume particles, bifrost, openvdb...) and still see direct or indirect volume noise? (tip: ...)
   
   → If Maya Fluids: You can increase Maya's fluidShape > Shading Quality > Quality to a higher value.
   → If OpenVDB Volumes: You can increase 3delightVDBShape node, you will see a Quality attribute (defaults to 0.5) which should bone tweaked until your quality demands match (typically a value of 1.0 is good for finals)   
   → If Volume Particles: ...coming soon
   → If Bifrost: ...coming soon
   
   

Further considerations

It is also possible that the cause of very specific noises in your scene might be related to:

• non-energy-conserving shaders / shading-networks
• non-energy-conserving settings
• any of the above but applied to objects which are not directly visible to the rendering camera (e.g. "behind" the camera)
• lack or mis-use of color management

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