pnmhistmap



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




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 dou-
       ble 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

       -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  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.


       -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 particu-
       larly 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 1993      Pnmhistmap User Manual(0)

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