RegionBinarize
RegionBinarize[image,marker,d] gives a binary version of image that includes the foreground pixels of marker and also connected regions whose pixel values are within a distance d.
RegionBinarize[image,marker,d,{t1,t2}] grows regions in marker by adding pixels whose average intensity is also constrained within an interval {t1,t2}.
Please visit the official Wolfram Language Reference for more details and examples on core symbols.