Initial lookup radius [px] – Number of pixels specifying the radius of the initial photon merging. Increasing the radius leads to faster resolution of caustics, however the individual photons can be visible on the final image.
Motion blur radius – Controls the correct resolution of motion blur in caustics. Increasing the parameter leads to faster resolution, while lowering it leads to more correct, albeit slower resolution.
Photons per pixel – The caustic solver will attempt to deliver at least this number of photons to each image pixel that contains caustics. Increasing this number will lead to faster resolution of caustics, but it will also increase memory cost and lead to slower convergence of non-caustics part of the scene.
Dispersion – Controls the correct resolution of dispersion in caustics. Increasing the parameter leads to faster resolution, while lowering it leads to more correct, albeit slower resolution.
Max photon repeat – Limits – Limits how many times the same photon gets repeated during photon emission. This is the tradeoff between rendering performance and physical accuracy. Lower values suppress noise and fireflies, but produce inaccurate caustics. Higher values produce accurate caustics, but also more noise in the image.
Enable caustics adaptivity – If enabled, caustic solver won't compute caustics that are very weak in order to save computational resources. This option is on by default and should be disabled only if caustic-related issues appear (such as disappearing of caustics or black spots visible in caustics render element).
Internal/Debugging
Usefulness ratio – Controls the preference of photon merging technique over path tracing when estimating image. Increasing this value will lead to preferable usage of photons, while decreasing it will lead to more utilization of path tracing.
Alpha (radius reduction) – Controls the speed of radius reduction. Setting this parameter to 1 disables radius reduction, which leads to faster convergence, however the caustics may remain blurry. Lowering this parameter leads to slower convergence, but less blurry caustics.
