hello, How can i use the labelling of regions obtained from Random Walker algorithm as input to watershed algorithm

I have been trying to segment lung tumors from CT images using Random walk & watershed algorithms.the steps included in my algorithm in brief are: 1.Read user defined seed points, to mark the tumor and non tumor regions. 2.Apply Random Walker Algorithm, given a set of user-defined (pre-labeled) pixels as labels, the probability of walking from each unlabeled pixel to each labeled pixel is calculated. 3.A vector of probabilities for each unlabeled pixel is defined. 4.Combine the vector of probabilities obtained for each unlabeled pixel, and assigned to one of the labels using the Marker controlled watershed algorithm to obtain tumor segmentation.

i dont understand the procedure to apply Watershed Algorithm.Please help.