Hi Lee (?),
to comment on the picture, it would be good to know
- the “not so high” values that you picked, in particular for -ad,
- what the BSDF represents,
- under what conditions this is rendered (sunny, clear sky?), and
- if the ambient cache was disabled (-aa 0).
My assumption is that the ambient cache was disabled. An indicator for this is the fine-grained “pixel-noise”, that would have been smeared out by the cache’s interpolation. The noise is then an expected artefact when you sample the BSDF at inadequately low resolution. Please try to increase -ad and see if this solves the issue.
Further interpretation requires more information about the model and rendering parameters.
Best, Lars.