Basic and Meyer's Watershed Transform

This example demonstrates the difference of basic watershed transform and Meyer's watershed transform.  Suppose that the brightness represents the altitude of the location, intensity surface can be regarded as a simple topographical surface. 
 

Left: Test image.  The surface has two minima (dark gray) where can be flooded early.  An object marker (dark circle) has been imposed on the right minima and a background marker has been placed at the boundary of the image (dark band).

Center: Basic watershed transform.  The water from the minima and the background marker is merged at the highest-crest line (bright band) and the water from two minima meets at pixels located at the equal distance from each minimum.

Right: Meyer's watershed transform.  The water floods from two markers so that the final watershed line is located at the highest-crest line only.  The result is a more meaningful or a more visually sensible segmentation.