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 ), 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

netpbm documentation                              13 July 2009                         Pnmhistmap User Manual(1)