By default, Final Gather is used in baking to calculate the first indirect bounce. This produces higher output quality than the upscaled Enlighten irradiance used for subsequent bounces. The Final Gather process casts rays from each pixel in the high resolution baked output texture, looking up the colour value of the hit location using high resolution ray-traced direct light and low resolution irradiance textures. These colour values are combined to produce the lighting at that point.The available Final Gather control parameters are:

EnableFinalGather: Enable final gather. When disabled baking instead uses upsampled Enlighten irradiance directly.
FinalGatherQuality: The number of rays to cast for each output pixel during final gather.
FinalGatherNumSamples: The number of samples to cast rays from for each output pixel during final gather.
FinalGatherTransparency: Enable the evaluation of transparency during final gather. Results might be inconsistent with real-time output.
FinalGatherPostFiltering: Enable running of a de-noising filter after final gather for smoother output.This allows using much lower values for FinalGatherQuality, but can result in undesired smoothing out of sharp lighting features for some scenes.

This feature is enabled by default.

Set it using SetEnableFinalGather(), SetFinalGatherQuality(), SetFinalGatherNumSamples(), SetFinalGatherTransparency(), SetFinalGatherPostFiltering methods in IBakeInputProperties. Or set enableFinalGather, finalGatherQuality, finalGatherNumSamples, finalGatherTransparency and finalGatherPostFiltering in the indirect bake parameters when using the HLBS.

HLBS Example:

<bakeParams enableFinalGather="true">
<indirect finalGatherQuality="4096" finalGatherNumSamples="16" finalGatherTransparency="true" finalGatherPostFiltering="true"/>
</bakeParams>