Digital Light & Color

As I'm trying to fill small gaps in a mask, I can easily see how the Speck Size slider affects the mask reparation. I can't get a handle of the Threshold slider - it doesn't seem to do that much, but I'm not sure if I'm using it properly.

I believe what the threshold does is control how much lighter or darker the speck needs to be than all the pixels in its neighborhood in order to be removed. If your specks are much lighter or darker than the background, I would not expect the threshold to do much.