Sampling 21
The sampling panel controls the appearance and quality of the final render. It is where you select the rendering integrator and set it’s behavior.
Pixel Variance, a tolerance value used to determine when to automatically calculate additional samples. A lower value can reduce noise at the cost of more samples and rendering time.
*Pixel Variance and Adaptive Sampling* When the Pixel Variance is set to a number higher than 0, a feature called Adaptive Sampling is enabled. What this means is that after Renderman finishes sampling a pixel it will look at how much the pixel has changed from the previous sample. If that change is less that the threshold set by the pixel variance, Renderman will stop sampling that pixel. This leads to faster renders.
Min Samples sets a required minimal level of samples for each pixel. After this limit is reached, adaptive sampling is enabled and the pixel will stop rendering when either the pixel variance value is reached or the max sample count is hit. Entering '0' will automatically set the min samples to the square root of the max sample parameter.
Max Samples is used to limit the maximum amount of samples any pixel may receive. Rendering will stop at this point even if the pixel variance value is not reached. If the pixel variance is set to 0 then every pixel will render for this many samples.
Specular Depth is used to limit the maximum amount of bounces for reflections and refractions. If your scene has multiple shiny or glass objects, this limit may need to be raised to avoid image artifacts.
Diffuse Depth is used to limit the maximum allowed bounces for diffuse (dull) light-rays.
Incremental determines how the image is rendered. When enabled, the renderer will calculate one sample per pixel across the entire image and continue this round robin sampling until reaching the sample limits. When it is disabled, the renderer will calculate all samples per pixel before moving on. While non-incremental rendering is often faster, incremental allows you to see a low quality preview of the image much sooner. In addition, some features (such as checkpointing) and render integrators (such as PxrVCM or PxrUBP) require incremental rendering. If these features are used, this checkbox is ignored and incremental rendering is automatically enabled.
Integrator, used to select the rendering algorithm for sampling the 3D scene and produce an image. For more details refer to the Integrator page. In general, PxrPathTracer and PxrVCM are the most useful.
There is a separate panel of sampling controls that are used for the material preview image and Interactive Rendering. There are no integrator options in this panel as PxrPathTracer is automatically selected for preview rendering and IPR sessions.
Sampling parameters can be overridden on a per object basis using the Raytrace Overrides section of the object parameters. This allows you to have an object render to a different pixel variance, or even a different ray bounce count.