Octave, 37 31 3126 bytes
This function performs a morphological dilationmorphological erosion on the Astan (1-b) part of the "image" using conv2imdilateimerode, and then uses some arithmetic to make all three areas different symbols. Thanks @LuisMendo for -5 bytes!
@(b)imdilate(12*b-imerode(b,ones(3))-1+2*b