Sometimes you may have a scene which is adequately sampled by the adaptive sampler except for one or two problematic objects that still require more sampling. Adaptive sampling is on by default and is the recommended mode. If the pixel variance is zero, or if the min samples is set equal to max samples then fixed sampling is enabled. When the pixel variance is greater than zero, adaptive sampling is enabled. Of these three settings, only the maximum number of samples is required to be given if unspecified the minimum samples and the variance will have reasonable defaults based on the maximum sample count. The variance setting controls the threshold for how little subsequent samples change the pixel (i.e., lower values cause more samples and longer renders), while the minimum sample count helps to control the confidence that this threshold has been achieved (i.e., higher values cause more samples). If enough samples are added without changing the pixel much, the renderer stops sampling it. As each sample is added to a pixel the renderer looks to see how much the sample changes the pixel. Each pixel will be sampled any number of times between these two bounds. For this method, the render is given a maximum number of samples per pixel, as with fixed sampling, and also a minimum number of samples and variance threshold. The other choice, adaptive sampling, is slightly trickier but may be able to speed up renders significantly. Sample numbers that are powers of two may give less image variance than other numbers - for example, 256 is usually better than 257 or even 280. For incremental mode, this means it's the number of passes that it will take over the image to refine it. Of these, fixed sampling is the simpler approach the renderer is given a maximum number of samples per pixel and it renders until it has computed that many. With respect to the samples within each pixel, the other major choice is fixed vs. Adaptive SamplingĪdaptive sampling (2048 max samples, 1248 actual avg) Please note that frames with many AOVs and large resolution may require significantly more memory in incremental mode because RenderMan must keep the entire framebuffer in memory. Also, some renderer settings (e.g., PxrVCM and PxrUnified) may require this mode. However, the total render time may be longer. This allows one to get a quick sense of how the final image will look and to cancel it if it becomes clear that adjustments are needed. When displayed to a framebuffer the entire image appears swiftly in a rough and noisy form which then refines bit by bit over time. This goes until it has visited each pixel a sufficient number of times. Then it visits each pixel again and computes a second sample, etc. Here, the renderer goes round-robin and visits every pixel in the image, computing a single sample for each. Incremental mode is the other alternative. This is the traditional rendering mode if rendered to a framebuffer the image starts out all black and then appears to fill in tile-by-tile until the render is done. Nonetheless, when a given pixel is finally displayed it is showing the finished result. Small batches of pixels are worked on together and several of these batches may be done in parallel on multi-core machines. In non-incremental mode, the renderer essentially visits each pixel once and computes all of the samples for it in one go. One of the biggest choices for sampling is whether to use incremental or non-incremental mode.
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