The PMC kernel is a custom-mutating, unbiased kernel written for GPUs. It lets OctaneRender® resolve complex caustics and lighting.


Figure 1: The PMC kernel parameters


PMC Kernel Parameters

Maximum Samples - Sets the maximum number of samples per pixel before the rendering process stops. Higher values generate cleaner renders. There is no rule as to how many samples per pixel are required for a good render, it is dependent on the scene.

DiffuseAmount of diffusion, or the reflection of light photons at different angles from an uneven or granular surface. Used for dull, non-reflecting materials or mesh emitters. Depth - Gives the maximum number of diffuse reflections if GI Mode is set to Diffuse.

SpecularAmount of specular reflection, or the mirror-like reflection of light photons at the same angle. Used for transparent materials such as glass and water. Depth - Controls the number of times a ray refracts before dying. Higher values mean higher render times, but more color bleeding and more details in transparent materials. Low values can introduce artifacts or turn some refractions into pure black.

Scatter Depth - The maximum path depth that allows scattering.

Maximal Overlapping Volumes - Determines how much space to allocate for overlapping volumes. Ray marching is faster with low values but it can cause artifacts where many volumes intersect.

Ray Epsilon - Determines the shadow ray offset distance.

Filter Size - The film splatting width to reduce aliasing.

Alpha Shadow - Allows any object with transparency (Specular materials, materials with Opacity settings and Alpha Channels) to cast a shadow instead of behaving as a solid object.

Caustic Blur - Increasing this value results in less caustic noise.


Figure 2: A comparison of various Caustic Blur values


GI Clamp - This clamps the contribution for each path to the specified value. By reducing the GI Clamp value, you can reduce the amount of fireflies caused by sparse but very strong contributing paths. Reducing this value reduces noise by removing energy.

Nested Dielectrics - If disabled, the surface IORs are not tracked and surface priorities are ignored.

Irradiance Mode - Displays the rendering with light energy but without material characteristics.

Max Subdivision Level - The maximum subdivision level applied on the scene geometry. A value of 0 disables this parameter.

Alpha ChannelA greyscale image used to determine which areas of a texture map are opaque and which areas are transparent. - Removes the background and renders it as transparent (zero alpha). This is useful if you want to composite the render over another image and don't want the background to be present.

Keep Environment - Use this option in conjunction with the Alpha Channel setting. The background renders with zero alpha, but is still visible in the final render. This allows more flexibility in compositing images.

AI Light - Enables AI lights. AI light functionality learns from the scene, and rendering becomes more efficient as more samples are rendered. When used with Adaptive SamplingA method of sampling that determines if areas of a rendering require more sampling than other areas instead of sampling the entire rendering equally., AI Light becomes even more effective as it learns pixel and light importance in a scene, and some pixels are no longer sampled.

AI Light Update - Enables dynamic updates to the AI lighting.

Light IDs Action - This parameter determines whether the L. IDs (Light IDs) and L. Inv (Light Inverse) buttons enable or disable lights with matching Light Pass ID numbers.

Light IDs & Light Linking Invert - See the section on Light Linking for more information.

Path Termination Power - High values increase render speed, but also creates more noise in dark areas.

Exploration Strength - This specifies how long the kernel investigates good paths before it tries to find a new path. Low values create a noisy image, while higher values create a splotchy image.

Direct Light Importance - Makes the kernel focus more on paths with indirect light. For example, imagine sunlight through a window, which creates a bright spot on the floor. If Direct Light Importance is set to 1, the kernel focuses its sampling on this area. If Direct Light Importance is reduced, the kernel reduces its efforts to sample that area, and focuses more on more tricky areas that are harder for light rays to reach.

Max Rejects - Controls the render's bias. Reducing the value creates more biased results, but the render time is shorter.

Parallel Samples - This controls how many samples OctaneRender® calculates in parallel. If you set it to a small value, OctaneRender® requires less memory to store the sample's state, but it renders a bit slower. If you set it to a high value, then OctaneRender® needs more graphics memory, making rendering faster. The change in performance depends on the scene and the GPUThe GPU is responsible for displaying graphical elements on a computer display. The GPU plays a key role in the Octane rendering process as the CUDA cores are utilized during the rendering process. architecture.

Work Chunk Size - The number of work blocks done per kernel run. Increasing this value also increases the memory requirement on the system, but it does not affect memory usage, and may increase render speed.

White Light Spectrum - Controls the appearance of colors produced by spectral emitters (daylight, environment, black body).This determines the spectrum that will produce white (before white balance) in the final image.

Toon Shadow Ambient - The ambient modifier to control Toon shadowing.