Octane PMC Kernel
PMC is a custom mutating unbiased kernel written for GPUs. It allows for complex caustics and lighting to be resolved.
Maximum Samples: This sets the maximum number of samples per pixel before the rendering process stops. The higher the number of samples per pixel, the cleaner the render.
Maximum Diffuse and Glossy Depth: The maximum number of times a ray can bounce/reflect/refract off a surface. Higher amounts mean also higher render time but more realistic results. For outdoor renders a good setting is around 4 maxdepth. For lighting the interior with natural light (the sun and the sky) you will need higher settings such as 8 or higher. While high values are possible, in reality, rays will not usually go beyond the 16-ray depth.
Ray Epsilon: The ray epsilon is the distance to offset new rays, so they don't intersect with the originating geometry. This value should be left as the default.
Filter Size: This sets the pixel size for filter for the render. This can improve aliasing artifacts in the render. If the filter is set too high, the image can become blurry.
Alpha Shadows: If alpha maps are used in the scene, this setting controls whether the shadows will be calculated from the mesh geometry or from the alpha map.
Alpha Channel: This option removes the background and renders it as transparent (zero alpha). This can be useful if the user wants to composite the render over another image and does not want the background to be present.
Caustic Blur: This is used to approximate caustics on rough surfaces and increase or decrease the sharpness of caustic noise. A zero value provides the sharpest caustics, and increasing this value increases the blurring effect to make caustics appear softer.
GI Clamp: It clamps the contribution for each path to the specified value. By reducing the “GI clamp” value, you can reduce the number of fireflies caused by sparse but very strongly contributing paths. Reducing this value reduces noise by removing energy. On the other hand, “caustic blur” reduces noise by blurring caustics, but conserves energy.
Exploration Strength: This specifies how long the kernel investigates good paths before it tries to find a new path. L ow values can create a noisy image while larger values can create a splotchy image.
Direct Light Importance: The direct light importance makes the kernel focus more on paths with indirect light. For example, imagine sunlight through a window that creates a bright spot on the floor. If the direct light importance is 1, the kernel would sample this area a lot, although it becomes clean very quickly. If the direct light importance is reduced, the kernel reduces its efforts to sample that area and focuses more on more tricky areas that are harder to render.
Max Rejects: This can control the “bias” of the render. By reducing the value, the result will be more biased, but the render time will be shorter.
Parallelism: This is used to reduce the number of samples that are investigated in parallel to make caustics appear earlier at the expense of some performance.
Path Term(ination) Power: this is the path termination strategy. The default setting should be good in most cases. If some dark patches stay too noisy too long, you can lower the value, which will slow down rendering, but cause Octane to spend more time on those areas.