I'm using a renderer developed by other people, and I found there are fireflies. It is strange that in a completely diffuse scene, there are still fireflies presented.
To my understanding, I think it is possible to have fireflies in diffuse scene depending on what sampling strategy I use. For example, if I use a very small area light, and the probability of hitting the light by sampling the BRDF will be very small, resulting in an extremely large radiance value. (I'm not sure because I also heard that fireflies will not appear in complete diffuse scene, so correct me if I'm wrong!)
I'm trying to locate the bug, if there are any, or improve the program, if the fireflies come with some reason. But after googling for a while, most things I found was how to fight fireflies, other than clearly analyzing where they come from.
I was wondering if anyone knows any good materials, or if you could kindly summarize a bit.
I'm particularly interested in the sources of the fireflies related to the sampling strategies, BRDF sampling, light sampling or MIS.
I also think fireflies should be considered separately with noise, since they also seem to be caused by numerical stability (from Wiki).