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 light, an object emitting light, or the world background. To find lights 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.
There are two sample methods that can be used: Path Tracing and Branched Path Tracing.
- Path Tracing
- 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 paths to trace for each pixel in the final render. As more samples are taken, the solution becomes less noisy and more accurate.
When using Branched Path Tracing, this changes the AA Samples which are multiplied by the Sub Samples and improve anti-aliasing.
- Number of samples for viewport rendering.
The panel is visible only when using Branched Path Tracing.
- Number of diffuse bounce samples to take for each AA sample.
- Number of glossy bounce samples to take for each AA sample.
- Number of transmission bounce samples to take for each AA sample.
- Number of ambient occlusion samples to take for each AA sample.
- Mesh Light
- Number of mesh light samples to take for each AA sample.
- Number of subsurface scattering samples to take for each AA sample.
- Number of volume scattering samples to take for each AA sample.
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.
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.
- Square Samples
- Square the amount of samples.
- Min Light 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.
- Min Transparent Bounces
- Minimum number of transparent bounces. Setting this higher reduces noise in the first bounces, but can also be less efficient for more complex geometry like hair and volumes.
- Light 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.
- Sample All Direct Lights
When enabled, Cycles will sample all lights in the scene for direct bounces, instead of randomly picking one. Disabling this can improve the performance, but will need a lot of Samples, to clear up the render.
Visible only when using Branched Path Tracing.
- Sample All Indirect Lights
Similar to direct light, but for indirect lights. This can reduce noise in scenes with many lights.
Visible only when using Branched Path Tracing.
- 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.