Help with flood filling segmentation

I am new to slicer. Working on segmentation using the SegmentEditorExtraEffects on Slicer build 4.10.2 on a Mac running 10.13.6.

I am trying to use flood filling to create a segmentation. I create a new segment, choose Flood Filling and leave default values (Int Tol 10, Neighborhood 1) and click on a pixel in the axial slice, get the spinning wheel but nothing happens (no region is selected for the segment). I change around the values and click and sometimes it processes with nothing happening and other times it gets stuck processing.

What does the “neighborhood size” parameter mean? What does increasing/decreasing it do?

Ultimately, I am trying to create a segment for a region where the intensity is above a certain value (a tumor region), but trying to avoid another region where there is also high intensity (other organs). Perhaps I should try another tool, like watershed, but I can’t figure out how to use that one.

Please use the latest stable release (Slicer-4.11.20200930), as it has greatly improved segmentation tools.

Flood filling is inherently a very fragile, unreliable operation on realistic images, and especially in 3D.

Grow from seeds, Watershed, and Local threshold effects all work much better. You can find detailed, step-by-step slide-based and video tutorials and segmentation recipes here: For example, see this recipe:

If you get stuck at any point then let us know.