USAGE: trianglethresh [-g graph] infile outfile
USAGE: trianglethresh [-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 the triangle technique.

# DESCRIPTION: TRIANGLETHRESH automatically thresholds an image to binary # (b/w) format. It does not assume the histogram is bimodal. It finds the # bin with the highest value (the peak in the histogram) and also the end # of the histogram furthest from the peak. It then draws a line between # the two. It exhaustively searches along the line drawing a perpendicular # from the line to the top of each histogram bin and picks the threshold # value at that bin for which the perpendicular is the longest.

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_triangle.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

Mathematics Background (120KB 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.