The Dilate function dilates the bright areas of the image over the less bright areas. If you wish to dilate the darker areas then convert the image to a negative of itself, apply the Dilate function, then convert the image back again by applying the negative conversion again.

 

Before:

 

After Dilating by a radius of 5:

 

Before:

 

After Dilating by a radius of 5:

 

Before:

 

After Dilating by a radius of 5:

 

Before:

 

After Dilating by a radius of 5:

 

Before:

 

After Dilating by a radius of 5: