Troubleshooting Fireflies And Noise In Blender Cycles

Understanding Fireflies and Noise

Fireflies and noise are common rendering artifacts that can degrade image quality in Blender Cycles. Identifying the causes and applying targeted fixes is key to achieving clean, professional renders.

Fireflies manifest as small bright pixels that flicker on and off between frames. They occur when a ray sample receives an unusually high amount of light energy. This sporadic spike causes the bright spot.

Noise refers to graininess in the render caused by variance between samples. Parts of the image appear blotchy because some ray samples receive more light than others.

Both issues stem from an inadequate sample count in areas of high variance. The sample count defines the number of rays traced per pixel. More samples smooth out the differences to eliminate fireflies and noise.

Common Causes of Fireflies

Clamping Settings Too High

Clamping sets an upper limit on ray intensity. Any rays that exceed the clamp value are truncated. If the clamp values are too high, bright rays can still get through to cause fireflies.

Reducing clamp levels prevents excessively bright samples. But setting clamps too aggressively can flatten contrast and light ranges.

Not Enough Samples

Insufficient sampling is the foremost cause of fireflies. Areas of high variance require more samples to smooth out variation between rays.

Indirect ray depth also impacts sampling noise. At bounce depths beyond the max value, samples are more likely to vary widely in intensity.

Glossy Materials Reflecting Caustics

Caustics are concentrated patches of light created from rays focused through reflective or refractive materials. Common with glass, water, and glossy surfaces.

As rays converge and diverge from caustics, sample variance increases. This makes fireflies more likely to occur in associated reflections.

Common Causes of Noise

Not Enough Samples

Low sample counts yield high variance between ray intensity. This variance manifests as blotchy noise in the render.

Higher samples per pixel smooth out the differences for cleaner results. Though samples exhibit diminishing returns and high values slow renders.

Weak Indirect Lighting Settings

Noisy renders often stem from underpowered indirect lighting and material settings. Low glossy bounces, few diffuse bounces, and low transmission settings introduce variance.

Higher values reduce noise at a performance cost. Balancing quality and render times is key for efficiency.

Identifying the Source of Issues

Isolating and simplifying scene components is crucial for diagnosing the factors causing fireflies and noise.

Isolating Parts of Scene

Temporarily hiding objects allows you to rule out sources of issues. If fireflies disappear when removing an object, then focus fixes there.

Simplifying Materials

Replace glossy shaders with diffused matte shaders to simplify reflections and isolate influencing materials.

Convert glass, liquids, and dispersion effects to basic translucent shaders to remove complex refractive caustics.

Adjusting Render Settings

Start with all indirect lighting settings at default levels before tuning them up to meet quality and performance needs.

Reduce clamp levels to help identify excessive intensity rays then fine tune clamping for your scene.

Fixing Fireflies

Clamping Firefly Properties

Lower light path clamp values until bright pixels disappear. Clamp both ray intensity and ray depth to control fireflies.

Narrow clamp thresholds carefully to retain contrast while eliminating spikes.

Increasing Sample Count

Add samples until variance is smoothed across pixels. Use higher values for glossy bounces and caustics.

Higher sample counts greatly increase render times. Use other fixes first before pushing samples too high.

Changing Material Properties

For glossy surfaces causing issues, lower the glossiness value to make reflections more diffuse.

For refractive materials like glass, lower the IOR ratio to simplify ray bending and caustic patterns.

Fixing Noise

Increasing Sample Count

Render longer to collect more samples per pixel. Find the sweet spot between noise reduction and practical render times for your scene.

Use adaptive sampling to maximize quality for the sample budget. This concentrating samples in noisy areas.

Adjusting Indirect Lighting Settings

Push up bounce counts and quality levels for glossy and transmission rays until noise resolves while avoiding fireflies.

Higher values greatly increase render times. Make incremental changes observing the impact on noise reduction.

Denoising Render

Use OpenImageDenoise to selectively smooth noise while preserving detail. This allows faster renders with lower samples.

Denoising works best after adjusting scene to reduce base noise levels.

Example Scene Diagnosis and Fixes

Analyzing specific problem cases in example scenes helps illustrate techniques to resolve various firefly and noise issues:

Step-by-Step Changes to Settings and Materials

Methodically modify key lighting, material, and render properties while observing impact on artifacts:

• Clamp intensity settings
• Light pathway bounce counts
• Material roughness and IOR
• Sample counts

Before and After Images of Improvements

Compare renders before and after adjustments to demonstrate reduction in fireflies and noise with each step.

Annotate exact settings changed to assist in explaining the differences made by each modification.

Extra Tips for Clean Renders

Some additional techniques can help tackle stubborn firefly and noise issues:

Using Portals and Mesh Lights

Portals guide sampling between adjoining spaces to reduce noise and artifacts.

Mesh emitters provide localized lighting without intense caustics from small light sources.

Baking Lighting

Precompute lighting with baked indirect illumination to greatly reduce render times.

Use render layers and passes for fine control over quality factors.

Bakes extend GPU rendering performance by reducing sampling requirements.