The Euclidean Distance Map (EDM) is important as the basis for a technique called watershed segmentation that can separate features which touch each other. The EDM has values that rise to a maximum in the center of each feature. Plotting these values as a surface represents each separate feature as a mountain peak. If you imagine rain falling onto this terrain, the drops run down each mountain and the lines at which drops from two different mountains meet are the watershed lines. Removing those lines separates the features so that they can be measured individually. This interactive tutorial illustrates the result of watershed separation of touching objects.

The tutorial initializes with a randomly selected specimen imaged in the microscope appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of images, in addition to the initial randomly chosen one. The Original button shows the original grayscale image, the Thresholded Binary button shows the result of thresholding this to produce a binary image, and the Watershed button shows the result of applying watershed segmentation.

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