Pnmhistmap User Manual(0)             Pnmhistmap User Manual(0)



Table Of Contents


NAME
       pnmhistmap - draw a histogram for a PGM or PPM file


SYNOPSIS
       pnmhistmap

       [-black]

       [-white]

       [-max N]

       [-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 fol-
       lowing histogram:

       image histogram from image

       If the input is PBM, pnmhistmap produces an  error  mes-
       sage and no output image.


OPTIONS
       -red

       -green

       -blue  Include the indicated color component in the out-
              put.  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 val-
              ues 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 max-
              pixval.

              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 plot-
              ted 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 sepa-
       rately 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 unread-
       baly 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.


       -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 pnmdepth or by  cutting  and  scaling  the
       lower-value side of the histogram.  Neither is a partic-
       ularly elegant solution to the problem.

       The program does not allow you  to  specify  the  output
       size.


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


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



netpbm documentation    25 October 199Pnmhistmap User Manual(0)
