sampling

#Introduction# What is sampling?

In computer graphics images are precisely painted by a computer program based on numbers. To know what color to draw for each pixel the program needs to perform many calculations and then estimate the final color for that single pixel. The precision in the result is determined by the amount of samples taken.

#Sampling Settings# Properties > Render > Sampling

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.
Note Pixel Variance only applies to adaptive sampling, When pixelvariance is greater than zero, adaptive sampling is enabled. However, if you set minsamples equal to maxsamples, the sampling is fixed and is no longer adaptive.

Min Samples, used to set 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, 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, used to limit the maximum amount of bounces for reflections and refractions.
Diffuse Depth, 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 disabled the renderer will calculate all samples per pixel before moving on. While non-incremental rendering is usually 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) require incremental rendering. In these cases 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, PathTracer and VCM are most useful.

Helpful Tip: The max depths don't need to be set very high in order to capture most lighting interactions. Unless you have transparent/refractive objects (like glass) both diffuse and specular depth limits can be set as low as 2 or 3.

The sampling Depth budgets may be overridden with Trace sets or per object in Properties > Object > Ray Tracing > Override Default Ray Tracing. Integrator specific attributes may also limit their effect.