Path Tracing


The Path Tracing and PMC render kernels are the best choices for rendering photorealistic images. The increase in quality comes with the cost of increased render times. Path Tracing may have difficulty rendering scenes that use small light sources, and may not render proper caustics well. In these situations, the PMC render kernel is the better choice. Testing renders using each of the render kernels is the best way to determine what kernel is the best choice for a given scene.


Path Tracing Parameters


Max. Samples 

Sets the maximum number of samples per pixel before the rendering process stops. Higher values result in cleaner renders. There is no rule as to how many samples per pixel are required for a good render - it depends on the content and complexity of the scene being rendered.


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 numbers mean higher render times, but more color bleeding and more details in transparent materials. Low numbers introduce artifacts or turn some refractions into pure black.

Examples of various Specular Depths using the Direct Lighting kernel with GI Mode set to None are shown in Figure 1.


Figure 1: A comparison of renderings using different Specular Depth settings.


Scatter Depth

The maximum path depth that allows scattering.


Ray Epsilon

The distance between the geometry and the light ray when calculating ray intersections for lighting and shadowing. Larger values push rays away from the geometry surface. Lower values are more accurate, but cause artifacts on large or distant objects. Ray Epsilon is similar to ray tracing bias in other rendering engines. Adjust Ray Epsilon to reduce artifacts in large-scale scenes.


Filter Size

Sets the filter size in terms of pixels. This improves aliasing artifacts in the render. However, if the filter is set too high, the image can become blurry.


Alpha Shadows

This enables direct light through Opacity maps. If disabled, ray tracing is faster, but it renders incorrect shadows for alpha-mapped geometry or Specular materials with fake shadows enabled. Alpha Shadows 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

Reduces noise in caustic light patterns. High values result in soft caustic patterns (see Figure 2).


GI Clamp

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.


Irradiance Mode

This renders the first surface as a white Diffuse material. Irradiance Mode is similar to Clay Mode, but it applies to just the first bounce. It disables the Bump channel and makes samples that are blocked by back faces transparent.


Max Subdivision Level

The maximum subdivision level that should be applied on the geometry in the scene. A value of 0 disables subdivision.


Alpha ChannelA greyscale image used to determine which areas of a texture map are opaque and which areas are transparent.

Removes background images or colors created by the SunSky environment node from the rendered image while not affecting any lighting cast by the environment. This is useful if the you want to composite the render over another image without the background being present. Objects appearing in the RGB channels have a bleeding edge, which appear as noise artifacts, but these edges are not included in the Alpha Channel itself.


Keep Environment

Used in conjunction with the Alpha Channel setting. It makes the background visible in the rendered image while also keeping the Alpha Channel.


AI Light

Enables or disables the AI light functionality. Please refer to the Octane Standalone documentation for more information on AI lights.


AI Light Update

Enables dynamic AI light updating.


Light IDs Action

Enables or disables actions to be taken on selected light IDs.


Light IDs

Globally enables or disables light IDs.


Light Linking Invert

Inverts the light linking behavior for the selected light IDs.


Path Termination Power

Provides a system to tweak samples per second vs. convergence (how fast noise vanishes). Higher values cause the kernels to keep paths shorter and spend less time on dark areas, which means they stay noisy longer, but it increases the samples per second. Lower values cause kernels to trace longer paths on average and spend more time on dark areas. In short, high values increases the render speed, but lead to more noise in dark areas.


Coherent Ratio

Increasing this value increases the render speed, but it introduces low-frequency noise or blotches. Eliminating the blotchy appearance requires a few hundred or even a few thousand samples per pixel, depending on the scene's contents.


Static Noise

Keeps noise patterns static between rendered frames in a sequence. The noise is static as long as the same 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 is used for rendering. Different architectures produce different numerical errors, which manifest as small differences in the noise pattern.


Parallel Samples

Controls how many samples OctaneRender® calculates in parallel. Smaller values require less memory to store the sample's state, but causes slower renders. High values require more memory, but reduce the render time. The change in performance depends on the scene and the GPU architecture.


Maximum Tile Samples

Controls the number of samples per pixel that OctaneRender will render before storing the result in the render buffer. Higher values mean that results arrive less often in the film buffer.


Minimize Net Traffic

Distributes the same tile to the net render slaves until OctaneRender reaches the maximum number of samples per pixel for that tile, and then it distributes the next tile to slaves. This option doesn't affect work done by local GPUs. A Render Node can merge all of its results into the same cached tile until the master switches to a different tile.


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.

Enables Adaptive Sampling. Adaptive sampling disables sampling for pixels that have reached a specified noise level. This lets you increase the maximum samples quite high (more than 30,000) and then rely on the adaptive sampling to figure out what pixels need or don't need that many samples. This feature is useful in scenes that have areas that are a lot more noisy than other areas. Adaptive sampling is possible only for direct lighting and the path tracing kernels.


Noise Threshold

Specifies the smallest relative noise level. When the noise estimate of a pixel is 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.


Minimum Adaptive Samples

Specifies the minimum number of samples to calculate before adaptive sampling kicks in. A pixel's noise estimate has a large initial error. The higher you set the noise threshold, the higher you should also set this parameter to avoid artifacts.


Pixel Grouping

Specifies the number of pixels handled together. When all of the pixels in a group reach the noise level, sampling stops for all of these pixels.


Expected Exposure

This value should be close to the same value as the image's exposure, or 0 (the default value) to ignore these settings. Adaptive sampling uses this parameter to determine what pixels are bright and dark, which depends on the Octane Imager's exposure setting. If the value is not 0, adaptive sampling adjusts the noise estimate of the image's very dark areas. It also increases the Min. Adaptive Samples limit for very dark areas, because very dark areas tend to find irregular paths to light sources, resulting in over-optimistic noise estimates.


Deep ImageRenders frames with multiple depth samples in addition to typical color and opacity channels.

Enables deep pixel image rendering for deep image compositing. For more information, see the Deep Image Rendering topic in the Octane Standalone documentation.


Deep Render PassesRender passes allow a rendered frame to be further broken down beyond the capabilities of Render Layers. Render Passes vary among render engines but typically they allow an image to be separated into its fundamental visual components such as diffuse, ambient, specular, etc..

Includes render passes for deep image pixels.


Maximum Depth Samples

When Deep Image Rendering is enabled, this sets the maximum number of depth samples per pixel. It is described in more detail in the Deep Image Rendering topic of this manual.


Depth Tolerance

When Deep Image Rendering is enabled, OctaneRender merges the depth samples whose relative depth difference falls below this value.


Toon Shadow Ambient

This is the ambient modifier of Toon Shadowing.


Emulate Old Volume Behavior

This is for previous scenes with Volume geometry that are set up using the former volume rendering system in earlier versions of OctaneRender®. When enabled, older scenes built with earlier versions render using the former volume rendering system. When disabled, OctaneRender® renders volumes using the new volume rendering system, and any pre-existing volumes must be set up again in order to render correctly. This is disabled by default, assuming that there no pre-existing volumes in the scene.