Even with setting my sampling numbers pretty high (256 diffuse and glossy samples times 16 render passes with branched path tracing) I'm still getting the very hot pixels. I read that this is caused by out-of-range sample values which the render engine never really blends in with other render passes, almost like the pixel has NaN (Not a Number) as a value. Or maybe it's more like a pixel has a value of 400, and no matter how many passes you average it with, it's still going to be really hot.
It seems that an engine should be able to filter out these extreme values, (like a median filter?) but on the other hand I hate doing something like clamping my render values because I need to keep the engine non-biased. (this will eventually be for a research project and it's vital that it be good math and a non-biased render engine. So maybe I'll need to purchase a very good non-biased engine.)
Am I correct that any method for removing outliers would then make it a biased render engine? Biased or not, numeric accuracy in the final image is the goal, so maybe even if it is technically biased with outlier removal, it might still be more accurate?
I'm not looking for techniques, such as "just blur it in Photoshop" but more theory of the rendering engine. Thanks very much for your help.
=== Update: I've found that the bright blue noise (from my emitter sky dome?) comes strictly from the Subsurface Indirect channel. I'll have to read up on subsurface scattering to make sure I'm not doing something stupid, but as strongly as this noise comes through, it makes me wonder if it's a bug in Cycles.