The integrator is the rendering algorithm used to compute the lighting. Cycles currently supports a path tracing integrator with direct light sampling. It works well for various lighting setups, but is not as suitable for caustics and some other complex lighting situations.
Rays are traced from the camera into the scene, bouncing around until they find a light source such as a lamp, an object emitting light, or the world background. To find lamps and surfaces emitting light, both indirect light sampling (letting the ray follow the surface BSDF) and direct light sampling (picking a light source and tracing a ray towards it) are used.
- Sample Method
- There are two integrator modes that can be used: Path Tracing and Branched Path Tracing.
- Square Samples
- 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.
- Render Samples
- Number of paths to trace for each pixel in the final render. As more samples are taken, the solution becomes less noisy and more accurate.
- Preview Samples
- Number of samples for viewport rendering.
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.
- AA Render Samples
- Number of samples to take for each pixel in the final render. More samples will improve anti-aliasing.
- AA Preview Samples
- Number of samples for viewport rendering.
- Diffuse Samples
- Number of diffuse bounce samples to take for each AA sample.
- Glossy Samples
- Number of glossy bounce samples to take for each AA sample.
- Transmission Samples
- Number of transmission bounce samples to take for each AA sample.
- AO Samples
- Number of ambient occlusion samples to take for each AA sample.
- Mesh Light Samples
- Number of mesh light samples to take for each AA sample.
- Subsurface Samples
- Number of subsurface scattering samples to take for each AA sample.
- 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.
- Max Bounces
- Maximum number of light bounces. For best quality, this should be set to the maximum. However, in practice, it may be good to set it to lower values for faster rendering. Setting it to maximum 0 bounces results in direct lighting only.
- Min Bounces
- 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.
- Diffuse Bounces
- Maximum number of diffuse bounces.
- Glossy Bounces
- Maximum number of glossy bounces.
- Transmission Bounces
- Maximum number of transmission bounces.
- Volume Bounces
- Maximum number of volume scattering bounces.
- Transparency Max
- Maximum number of transparency bounces.
- Transparency Min
- Minimum number of transparency bounces, after which Russian Roulette termination is used.
- Transparent Shadows
- For direct light sampling, use transparency of surfaces in between to produce shadows affected by transparency of those surfaces.
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.
- Filter Glossy
When using a value higher than 0.0, this will blur glossy reflections after blurry bounces, to reduce noise at the cost of accuracy. 1.0 is a good starting value to tweak.
Some light paths have a low probability of being found while contributing much light to the pixel. As a result these light paths will be found in some pixels and not in others, causing fireflies. An example of such a difficult path might be a small light that is causing a small specular highlight on a sharp glossy material, which we are seeing through a rough glossy material. In fact in such a case we practically have a caustic.
With path tracing it is difficult to find the specular highlight, but if we increase the roughness on the material, the highlight gets bigger and softer, and so easier to find. Often this blurring will hardly be noticeable, because we are seeing it through a blurry material anyway, but there are also cases where this will lead to a loss of detail in lighting.
See Reducing Noise for examples of the clamp settings in use.