update readme

README.md

@@ -8,19 +8,29 @@ greyscale images.
 ## Installation ##
 Copy the jar file into the /plugins directory of your ImageJ installation.
 
-The plugin relies on the MorpholLibJ library, so the latest version of MorphoLibJ is requried as well.
+The plugin relies on the [MorphoLibJ library](https://github.com/ijpb/MorphoLibJ),
+so the latest version of MorphoLibJ is required as well.
 
 ## Usage ##
 
 After installation, a new "Granulometry" menu appears within the plugins menu. It allows:
 * running granulometry on a single image
 * running granulometry on a collection of images.
 
-Several structuring element shapes may be chosen: square, disk, diamond, octagon, line segments with various orientations.
+
+Several structuring element shapes may be chosen: square, disk, diamond, octagon, 
+or line segments with various orientations.
 
 Several operation may be applied: erosion, dilation, closing or opening.
 
+The difference between the radius-based and the diameter-based granulometries rely on the 
+way the structuring element is computed. Structuring elements defined from a diameter can
+have a larger variety of sizes, but the symmetry of the structuring element is not 
+warranted. Moreover, if can not be used for some structuring elements (eg "diamond").
+
+
 ## known bugs and limitations ##
 
 The "diamond" structuring element can not be defined with even diameters.
-Also, the resulting granulometric curves may be more or less "spiky" due to discretization effects of the structuring element.
+Also, the resulting granulometric curves may be more or less "spiky" due to 
+discretization effects of the structuring element.