pnmhistmap - draw a histogram for a PGM or PPM file


   pnmhistmap [-black] [-white] [-max N] [-verbose] [pnmfile]


   Reads  a portable anymap as input, although bitmap (PBM) input produces
   an error message and no image.  Produces an image showing  a  histogram
   of  the  color  (or  gray)  values in the input.  A graymap (PGM) input
   produces a bitmap output.  A pixmap (PPM) input produces pixmap  output
   with  three  overlaid  histograms: a red one for the red input, a green
   one for the green input, and a blue one for the blue input.  The output
   is fixed in size: 256 pixels wide by 200 pixels high.


   -black Ignores the count of black pixels when scaling the histogram.

   -white Ignores the count of white pixels when scaling the histogram.

   The  -black  and  -white  options,  which  can  be  used  seperately or
   together, are useful for images with a large percentage of pixels whose
   value  is  zero or 255, which can cause the remaining histogram data to
   become unreadbaly small.  Note that, for pixmap inputs,  these  options
   apply  to  all colors; if, for example, the input has a large number of
   bright-red areas, you will probably want to use the -white option.

   -max N Force the scaling of the histogram to use N as the largest-count
          value.   This  is  useful  for inputs with a large percentage of
          single-color pixels which are not black or white.

          Report the progress  of  making  the  histogram,  including  the
          largest-count value used to scale the output.

   All flags can be abbreviated to their shortest unique prefix.


   Assumes  maxval  is always 255.  Images with a smaller maxval will only
   use the lower-value side of the histogram.  This can be overcome either
   by  piping  the  input through "pnmdepth 255" or by cutting and scaling
   the lower-value side of  the  histogram.   Neither  is  a  particularly
   elegant solution.

   Should allow the output size to be specified.


   pgmhist(1), ppmhist(1), pgm(5), ppm(5)


   Wilson H. Bent. Jr. (

                            25 October 1993                  pnmhistmap(1)


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.