The 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. attribute is a rendering option that disables sampling for pixels that reach a specified noise threshold, which allows the Kernel to focus its processing on areas that still need refinement. Adaptive sampling is available with the Direct Light, Path Tracing, and Photon Tracing KernelsBy definition, this is the central or most important part of something. In Octane, the Kernels are the heart of the render engine. (figure 1).
Figure 1: The Adaptive Sampling rollout in the Kernel's Attribute Editor window
Enable Adaptive Sampling - Enables this feature.
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.
Min. 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 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.