Watershed Segmentation
Watershed is a segmentation method where waters are flooded through the image , and make all the low lying areas of image submerge in water, so that remaining high lying areas(pixels) are edges. This way it provides clear boundary of image and this method is one of efficient method to identify the edges. Different approaches may be employed to use the watershed principle for image segmentation :- Local minima of the gradient of the image may be chosen as markers, in this case an over-segmentation is produced and a second step involves region merging. Marker based watershed transformation make use of specific marker positions which have been either explicitly defined by the user or determined automatically with morphological operators or other ways. How to obtain watershed lines :- Remove minima which are not required(irrelevant) merge the regions obtained(sub-regions