USAGE: otsuthresh [-g graph] infile outfile
USAGE: otsuthresh [-help]

-g ..... graph .......... graph specifies whether to generate a
......................... histogram graph image displaying the
......................... location and value of the threshold;
......................... choices are: view or save;
......................... default is no graph

PURPOSE: To automatically thresholds an image to binary (b/w) format using Otsu's technique.

DESCRIPTION: OTSUTHRESH automatically thresholds an image to binary (b/w) format. It assume the histogram is bimodal, i.e. is the composite of two bell-shaped distributions representing the foreground and background classes. The Otsu appoach computes the Between Class Variance from the foreground (above threshold data) and background (at and below threshold value) for every possible threshold value. The optimal threshold is the one that maximizes the Between Class Variance. This is equivalent to finding the threshold that minimizes the overlap between the two bell-shaped class curves.

ARGUMENTS:

-g graph ... GRAPH specifies whether to generate a graph (image) of the histogram, displaying the location and value of the threshold. The choices are: view, save and none. If graph=view is selected, the graph will be created and displayed automatically, but not saved. If graph=save is selected, then the graph will be created and saved to a file using the infile name, with "_histog_otsu.gif" appended, but the graph will not be displayed automatically. If -g option is not specified, then no graph will be created.

NOTE: It is highly recommended that the output not be specified as a JPG image as that will cause compression and potentially a non-binary (i.e. a graylevel) result. GIF is the recommended output format.

REFERENCES: see the following:
http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Segmenta.html
http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/MORSE/threshold.pdf
http://www.cse.unr.edu/~bebis/CS791E/Notes/Thresholding.pdf
http://www.ifi.uio.no/in384/info/threshold.ps
http://www.supelec.fr/ecole/radio/JPPS01.pdf

Mathematics Background (256KB PDF)

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.