The Path Tracing kernel is best used for realistic results. The render times are higher than the Direct Lighting kernel, but the results are more photorealistic. It can have difficulties with small light sources and proper caustics, for which PMC is better suited.
Figure 1: The Path Tracing kernel parameters
Maximum Samples - This sets the maximum number of samples per pixel before the rendering process stops. The higher the value, the cleaner the render. 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 this 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 and without material characteristics.
Max Subdivision Level - The maximum subdivision level applied on a scene's 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 it also creates higher noise in dark areas.
Coherent Ratio - Increasing this value increases the render speed, but introduces low-frequency noise (blotches), which may require a few hundred or even a few thousand samples per pixel to go away, depending on the scene.
Static Noise - If enabled, the noise patterns are kept stable between frames.
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.
Maximum Tile Samples - This controls the number of samples per pixel that OctaneRender® will render until it takes the result and stores it in the film buffer. A higher value means that results arrive less often in the film buffer.
Minimize Net Traffic - If enabled, OctaneRender® distributes the same tile to the net render nodes until it reaches the max samples-per-pixel for that tile, and then it distributes the next tile to render nodes. Work done by local GPUs is not affected by this option. This way, a render node can merge all of its results into the same cached tile until the Primary Render Node switches to a different tile.
Adaptive Sampling - Stops sampling pixels that reach a specified noise threshold, which allows the kernel to focus its processing on areas that still need refinement.
Noise Threshold - When Adaptive Sampling is enabled, Noise Threshold specifies the smallest relative noise level. When the noise estimate of a pixel becomes less than this value, sampling switches off for this pixel. Good values are in the range of 0.01 - 0.03. The default is 0.02, which is pretty clean.
Min. Adaptive Samples - Specifies the minimum number of samples to calculate before adaptive sampling kicks in. The reason for this option is the fact that the noise estimate of a pixel is just an estimate with a fairly large initial error. The higher you set the noise threshold, the higher you should also set this value in order to avoid artifacts.
Pixel Grouping - When Adaptive Sampling is enabled, Pixel Grouping specifies the number of pixels that are handled together. When all pixels of a group reach the noise level, sampling stops for all of these pixels.
Expected Exposure - This value should be about the same value as the image exposure, or 0 (the default value) to ignore these settings. This parameter is used by Adaptive Sampling to determine the pixels that are bright and those that are dark, which depends on the exposure setting in the Octane Imager. If the value is not 0, Adaptive Sampling reduces the noise estimate of very dark areas in the image. It also increases the Min. Adaptive Samples limit for very dark areas, because very dark areas tend to find paths to light sources irregularly, resulting to an otherwise over-optimistic noise estimate.
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.
Deep ImageRenders frames with multiple depth samples in addition to typical color and opacity channels. - Enables rendering deep pixel images used for deep image compositing.
Deep Render AOVs - Includes AOVs in deep pixel rendering.
Max. Depth Samples - Used when Deep Image rendering is enabled. This sets the maximum number of depth samples per pixel. This is covered in the Deep Image Rendering topic of this manual.
Depth Tolerance - Used when Deep Image rendering is enabled. The depth samples whose relative depth difference falls below this tolerance value are merged together. This is covered in the Deep Image Rendering topic of this manual.
Toon Shadow Ambient - The ambient modifier to control Toon shadowing.