Reducing Noise In Cycles: Sampling And Integrator Settings

What is Noise in Cycles Renders?

Noise in Cycles renders manifests as graininess and random speckles in the final rendered image. It stems from the stochastic ray tracing process, where rays are cast randomly to simulate light behavior. As fewer rays are traced per pixel, variance in the light information leads to visible noise artifacts.

Noise occurs due to variance between pixels in the amount of rays captured. With higher samples settings, more rays are traced per pixel, converging light information and reducing variance to produce cleaner renders.

Causes of Noise in Ray Tracing

Low sample counts
Complex lighting interactions from bouncing rays
Caustics and volumetrics effects with scattered light rays
Denoising artifacts
Indirect illumination variance

Core Sampling Settings

The Render Properties panel controls the core sampling settings that affect noise.

Samples Setting and Convergence

The Samples setting determines the number of rays traced per pixel in the render. Higher samples values result in more rays traced, increasing render times but converging light information to reduce noise.

There is a correlation between less noise and higher samples values. But the convergence rate depends on scene complexity. Simpler scenes may converge fully at 128 or 256 samples, while complex scenes with lots of noise sources may need 1024 samples or more.

Using Branched Path Tracing

Branched path tracing in Cycles can optimize sampling to reduce noise faster. It traces diffuse and glossy bounce rays separately from specular and transmission rays to better handle difficult caustics.

Enabling branched path tracing helps with noise from indoor scenes with lots of bounced light. It carries a render time cost but can achieve cleaner results at equal samples compared to path tracing.

Clamping Settings

Clamping settings like Indirect Clamping provide thresholds to reduce noise from outlier rays. This can reduce noisy fireflies at a precision cost. Direct light clamping also controls outliers from direct illumination sampling.

Advanced Integrator Settings

The Cycles integrator has advanced settings to further tune sampling and noise behavior.

Light Paths and Bounces

The Max Bounces settings control how many times rays can bounce off surfaces. Higher bounce counts allow more indirect illumination, but increase noise.

Min Bounces forces more bounces to reduce noise from darkened spots. Diffuse bounces soften indirect lighting noise, while glossy bounces create brighter and noisier caustics.

Russian Roulette and Path Termination

Russian Roulette terminates ray paths randomly to reduce noise from over-bouncing. Lower values terminate more rays to prioritize reduced noise over accuracy.

Min Light Bounces sets the minimum path length for rays bouncing from light sources, for brighter and noisier single-bounce lighting.

Multiple Importance Sampling

Multiple Importance Sampling renders light and material samples separately then combines for faster convergence. MIS can reduce noise but comes at a render time cost.

Denoising Renders

Denoising is a post-process that attempts to reduce noise while preserving detail. It analyzes pixel neighborhood variance then blurs heterogeneous noise pixel clusters.

Using the Cycles Denoiser

Cycles includes the OpenImageDenoise AI denoiser. It is enabled via the Render Layers Post Processing panel. The denoiser can clean up moderate noise quickly, but loses fine texture detail.

Third-party Denoisers

There are many third-party denoisers for Blender to explore as alternatives, such as Optix, Alpaca, Synth, and B-Mesh. Each has different trade-offs for quality, retention of details, and artifacts.

Optimizing Scene and Lighting

Optimizing scenes to be simpler and more controlled also helps to reduce noise render times.

Simplifying Geometry

Reducing polygon count, subdivision, and particle systems decrease sampling required in those areas. Simplifying unnecessary geometry reduces overall samples needed.

Using Portals and Occlusion

Portals, occlusion planes, and culling limit ray samples to simplify lighting and indirect bounce effects. This concentrates samples in important areas.

Balancing Lighting and Materials

Having fewer, controlled light sources reduces noise from random intersections. Simpler glossy and diffuse materials need less sampling than glass, anisotropic, velvet, or volumetrics.

Example Scenes and Settings

Here we examine common test scenes and benchmarks for balancing noise reduction with render times when setting sample counts.

Comparing Noise in Different Test Scenes

Cornell Box: Simple direct and indirect illumination, converges quickly with 128-256 samples.
Bathroom Scene: Many materials and larger indirect illumination complexity, may need 512-1024 samples.
Archinteriors Bedroom: Lots of geometry, textures, secondary bounces. Requires high samples >1024 or denoising.

Recommended Settings for Common Use Cases

Product visualizations – Branched paths, 1024-2048 samples
Exteriors – Higher clamping, 512-1024 samples
Animation – Lower samples with heavy denoising
Architectural – Higher bounces, portals, 1024+ samples