Posted by Gabriel Landini on Oct 31, 2013; 3:59pm URL: http://imagej.273.s1.nabble.com/automatically-filling-8bit-objects-tp5005404p5005406.html
If you have a set of "rings" drawn with different greyscale values in an 8 bit
image and on a black background, you can fill them in the border colour using
the "Fill_Greyscale_Holes" macro in the Morphology collection here
http://www.dentistry.bham.ac.uk/landinig/software/software.html