Fred's ImageMagick Scripts



    Licensing:

    Copyright © Fred Weinhaus

    My scripts are available free of charge for non-commercial use, ONLY.

    For use of my scripts in commercial (for-profit) environments or non-free applications, please contact me (Fred Weinhaus) for licensing arrangements. My email address is fmw at alink dot net.

    If you: 1) redistribute, 2) incorporate any of these scripts into other free applications or 3) reprogram them in another scripting language, then you must contact me for permission, especially if the result might be used in a commercial or for-profit environment.

    Usage, whether stated or not in the script, is restricted to the above licensing arrangements. It is also subject, in a subordinate manner, to the ImageMagick license, which can be found at: http://www.imagemagick.org/script/license.php

PTILETHRESH


Automatically thresholds an image to binary (b/w) format at a specified percentile on the cumulative histogram.

Download Script

last modified: November 03, 2015



USAGE: ptilethresh [-p percentile ] infile outfile
USAGE: ptilethresh [-h or -help]

-p .... percentile .... percentile on cumulative histogram for
....................... desired threshold; 0<=float<=100; default=50

PURPOSE: To automatically thresholds an image to binary (b/w) format at a specified percentile on the cumulative histogram.

DESCRIPTION: PTILETHRESH automatically thresholds an image to binary (b/w) format at a specified percentile on the cumulative histogram. When the percentile is 50%, this technique is also known as balanced thresholding.

ARGUMENTS:

-p percentile ... PERCENTILE is the desired threshold point on the cumulative histogram. Values are floats between 0 and 100. The default=50.

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:
http://en.wikipedia.org/wiki/Balanced_histogram_thresholding
http://www.pvv.org/~perchrh/papers/datasyn/paper2/report.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.


EXAMPLES


PTILE Thresholding Of Various Images

Pictures Were Obtained from:
blood.jpg from http://www.istanbul.edu.tr/eng/ee/jeee/main/pages/issues/is62/62008.pdf
fingerprint.jpg from http://www.istanbul.edu.tr/eng/ee/jeee/main/pages/issues/is62/62008.pdf
flower.jpg from http://www.jhlabs.com/ip/blurring.html
house.jpg from http://en.wikipedia.org/wiki/Otsu's_method
kanji.jpg from http://www.measurement.sk/2004/S1/Yong.pdf
parts.gif from http://www.ph.tn.tudelft.nl/Courses/FIP/noframes/fip-Segmenta.html
rice.jpg from http://www.istanbul.edu.tr/eng/ee/jeee/main/pages/issues/is62/62008.pdf
tank.jpg from http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=ADA464347&Location=U2&doc=GetTRDoc.pdf
textsample.jpg from http://signal.ece.utexas.edu/seminars/dsp_seminars/01fall/211_seeger_mf.pdf
lena2g_edge1.jpg was created using the IM function -edge 1

Original Image

Thresholded Image



See A Comparison Of Each Image Against Each Thresholding Technique



What the script does is as follows:

  • Computes the complement of the percentile
  • Converts to grayscale
  • Linearly stretches the images so that the percentile value goes to black
    and the complement value goes to white

This is equivalent to the following IM commands

  • bpt=$percentile
  • wpt=`convert xc: -format "%[fx:100-$bpt]" info:`
  • convert $infile -colorspace gray -linear-stretch $bpt%,$wpt% $outfile