NAME

       pnmhistmap - draw a histogram for a PGM or PPM file

SYNOPSIS

       pnmhistmap

       [-red] [-green] [-blue]

       [-black] [-white]

       [-max N]

       [-lval] [-rval]

       [-height] [-width]

       [-dots]

       [-verbose]

       [pnmfile]

       Minimum  unique  abbreviation of option is acceptable.  You may use double hyphens instead
       of single hyphen to denote options.  You may use white space in place of the  equals  sign
       to separate an option name from its value.

DESCRIPTION

       This program is part of Netpbm(1).

       pnmhistmap  reads  a  PNM  image as input and produces an image showing a histogram of the
       color (or gray) values in the input.  A PGM input results in a PBM output.   A  PPM  input
       results  in  a  PPM  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.

       For example, from the following image produces the following histogram:

       image histogram from image

       If the input is PBM, pnmhistmap produces an error message and no output image.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common  Options ⟨index.html#commonoptions⟩ ), pnmhistmap recognizes the following command
       line options:

       -red

       -green

       -blue  Include the indicated color component in the output.  If you specify none of these,
              pnmhistmap include all three.

              These options are meaningless if the input is PGM.

              These  options  were  new  in Netpbm 10.26 (January 2005).  Before that, pnmhistmap
              always included all three color components.

       -dots  Plot the histogram as dots.  By default, pnmhistmap plots bars.

              Example of dots:.B -dots example

              This option was new in Netpbm 10.26 (January 2005).  Before that, pnmhistmap always
              plotted bars.

       -lval minpixval

       -rval maxpixval
              These options specify the range of intensity values to include.  pnmhistmap ignores
              intensities less than minpixval and greater than maxpixval.  So the  left  side  of
              the histogram corresponds to minpixval and the right side corresponds to maxpixval.

              By default, pnmhistmap plots the entire possible range: zero to the maxval.

              These  options  were  new  in Netpbm 10.26 (January 2005).  Before that, pnmhistmap
              always plotted from zero to the maxval.

       -height

       -width These options specify the dimensions, in pixels of the histogram image.

              The default height is 200 pixels.

              The default width is one pixel for each plotted intensity value (so it's controlled
              by  the  maxval of the image and the -lval and -rval options).  The "count buckets"
              in the histogram are always one pixel wide.  If you specify a width less  than  the
              number  of  plotted  intensity  values, a bucket represents more than one intensity
              value.  If you specify a width greater that the number of plotted intensity values,
              some buckets represent no color (the count is zero).

              This  option  was  new in Netpbm 10.26 (January 2005).  Before that, the dimensions
              were always what the default is today.

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

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

              The -black and -white options, which can be used separately 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  unreadably  small.   Note  that,  for
              color  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.

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

LIMITATIONS

       pnmhistmap  assumes  maxval is always 255.  Images with a smaller maxval will only use the
       lower-value side of the histogram.  You can overcome  this  either  by  piping  the  input
       through pamdepth or by cutting and scaling the lower-value side of the histogram.  Neither
       is a particularly elegant solution to the problem.

SEE ALSO

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

AUTHOR

       Wilson H. Bent. Jr. (whb@usc.edu).

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master
       documentation is at

              http://netpbm.sourceforge.net/doc/pnmhistmap.html