The primary rays that Karma XPU sends from the camera into the scene are called path traced samples. Path traced samples resolve anti-aliasing artifacts from small geometry detail (such as curves or displacement), depth of field, and motion blur. With Karma XPU the primary sampling control is Path Traced Samples. This sets the number of primary samples the XPU engine will project for each pixel.

Karma XPU supports pixel oracles, so it will cut off the number of path traced samples once the variance between pixels reaches the Variance Threshold. This should improve render times by reducing the amount of unnecessary work needed to converge renders to a clean result.

When a primary ray in Karma XPU hits an object, Karma will send two secondary samples by default: one direct sample toward a light, and one indirect sample into the scene. This simplicity can make Path Traced convergence very fast and interactive initially, but offers very few controls for resolving noise from specific secondary ray types in the scene. Light Sampling Quality will determine the number of times each light is sampled, but Karma decides how many lights to sample, based on the Light Sampling Mode. Karma XPU also randomly chooses the indirect sample lobe.

With an understanding of how sampling works in Karma XPU, next we’ll look at some practical tips to reduce noise in your renders.