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. disables sampling for pixels that reach a specified noise threshold, which allows the Kernel to focus its processing on areas that still need refinement. You can find the Adaptive Sampling options in the attributes for the Direct Light and Path Tracing kernels.
Figure 1: The Adaptive Sampling parameter of the Direct Light kernel
Figure 2: The Adaptive Sampling parameter of the Path Tracing kernel
Adaptive Sampling - Stops sampling pixels that reach a specified noise threshold, allowing 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 a pixel's noise estimate is less than this value, OctaneRender® switches off sampling for this pixel. Good values to use are in the range of 0.01 - 0.03. The default is 0.02, which is pretty clean.
Group Pixels - When Adaptive Sampling is enabled, Group Pixels specifies the number of pixels that are handled together. If all pixels of a group reach the noise level, sampling stops for all of these pixels.
Expected Exposure - You should set Expected Exposure to be about the same value as the image exposure, otherwise set it to 0 (the default value) to ignore these settings. Adaptive Sampling uses this parameter to determine what pixels are bright and dark - this depends on the exposure setting in the Octane Imager. If the value is not 0, Adaptive Sampling adjusts the noise estimate of very dark areas. It also increases the minimum adaptive samples limit for very dark areas, because very dark areas tend to find paths to light sources irregularly, resulting in an otherwise over-optimistic noise estimate.
Min. Adaptive Samples - Specifies the minimum samples to calculate before Adaptive Sampling kicks in. The noise estimate of a pixel is just an estimate with a large initial error. If you set Noise Threshold to a high value, you should also set Min. Samples to a high value to avoid artifacts.