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



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 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 pix-
	      els whose value is zero or 255, which can	 cause	the  remaining
	      histogram data to become unreadbaly 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  particu-
       larly elegant solution to the problem.


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


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



netpbm documentation		 13 July 2009	     Pnmhistmap User Manual(0)