Watershed - operates differently to description

Posted by Jeremy Adler on May 19, 2015; 2:01pm
URL: http://imagej.273.s1.nabble.com/Watershed-operates-differently-to-description-tp5012869.html


I have been playing the with watershed binary operation - it seems to work differently from the description provided.
       The description says watershed makes an erode to ultimate points, then dilates the points without allowing merging while keeping within the bounds of original binary object.
        see attached stack
The attached stack of images suggests it operated differently - based on the description of the watershed the object should be split midway between the two ultimate points - but it actually divides at a more sensible place.

my guess is that the software is examining the line of pixels between the two ultimate points, using the distance transform, and making the divide at the minima along this line.

In its current form the watershed is much better than described, but exactly how  is the watershed in ImageJ operating ?
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