This ImageJ plugin segments the image in classes by thresholding. It uses the same algorithm found in Otsu Thresholding, but was adapted to output more than 2 classes out of the process.
The method to use for thresholding. Currently only OTSU is available.
Bundled with Fiji. "Do all" is the great feature...
Extract image features based on one or more intensity thresholds, and output the result as a labeled image or as a region of interest.