- There are two integrator modes that can be used: Path Tracing and Branched Path Tracing.
- Square the amount samples.
Seed value for integrator to get different noise patterns.
- Animate Seed (clock icon)
- This button which can be found on the right side of the Seed value can be used to give different seed values. It is a good idea to enable this when making animation because in the real world each frame has a different noise pattern.
- Clamp Direct
This option limits the maximum intensity a sample from rays which have not yet bounced can contribute to a pixel. It reduces noise at the cost of accuracy. Setting this option to 0.0 disables clamping altogether. Lower have a greater affect (dimmer samples) on the resulting image than higher values.
A common issue encountered with Path Tracing is the occurrence of "fireflies": improbable samples that contribute very high values to pixels. This option provides a way to limit that. However, note that as you clamp out such values, other bright lights/reflections will be dimmed as well.
Care must be taken when using this setting to find a balance between mitigating fireflies and losing intentionally bright parts. It is often useful to clamp indirect bounces separately, as they tend to cause more fireflies than direct bounces. See the Clamp Indirect setting.
- Clamp Indirect
- The same as Clamp Direct, but for rays which have bounced multiple times.
- Light Sampling Threshold
- Probabilistically terminates light samples when the light contribution is below this threshold (more noise but faster rendering). Zero disables the test and never ignores lights. This is useful because in large scenes with many light sources, some might only contribute a small amount to the final image, and increase render times. Using this setting can decrease the render times needed to calculate the rays which in the end have very little affect on the image.
Random sampling pattern used by the integrator.
- Uses a Sobol pattern to decide the random sampling pattern used by the integrator. See Sobol sequence on Wikipedia for more information.
- Correlated Multi-Jitter
- Uses a Correlated Multi-Jitter pattern to decide the random sampling pattern used by the integrator. See this Pixar paper for more information.
- Layer Samples
When render layers have per layer number of samples set, this option specifies how to use them.
- The render layer samples will override the set scene samples.
- Bound render layer samples by scene samples.
- Ignore render layer sample settings.
The Path Tracing integrator is a pure path tracer; at each hit it will bounce light in one direction and pick one light to receive lighting from. This makes each individual sample faster to compute, but will typically require more samples to clean up the noise.
Branched Path Tracing¶
The non-progressive Branched Path Tracing integrator offers finer control over sampling. It is similar to Path Tracing, but at the first hit it will split the path for different surface components and will take all lights into account for shading instead of just one.
This makes each sample slower, but will reduce noise, especially in scenes dominated by direct or one-bounce lighting. To get the same number of diffuse samples as in the path tracing integrator, note that e.g. 250 path tracing samples = 10 AA samples x 25 diffuse samples. The Sampling panel shows this total number of samples.
- Number of samples to take for each pixel in the final render. More samples will improve anti-aliasing.
- Volume Samples
- Number of volume scattering samples to take for each AA sample.
- Sample All Direct Lights
- When enabled, Cycles will samples all lights in the scene for direct bounces, instead of randomly picking one. Disabling this can improve performance, when using a lot of AA Samples anyway, to clear up the render.
- Sample All Indirect Lights
- Similar to direct light, but for indirects lights. This can reduce noise in scenes with many lights.
- Minimum number of light bounces for each path, after which the integrator uses Russian Roulette to terminate paths that contribute less to the image. Setting this higher gives less noise, but may also increase render time considerably. For a low number of bounces, it is strongly recommended to set this equal to the maximum number of bounces.
- Volume Bounces
- Maximum number of volume scattering bounces.
Caustics & Filter Glossy¶
- Reflective Caustics
- While in principle path tracing supports rendering of caustics with a sufficient number of samples, in practice it may be inefficient to the point that there is just too much noise. This option can be unchecked, to disable reflective caustics.
- Refractive Caustics
- The same as above, but for refractive caustics.
See Reducing Noise for examples of the clamp settings in use.