Ppmhist User Manual(0)					Ppmhist User Manual(0)



NAME
       ppmhist - print a histogram of the colors in a PPM image


SYNOPSIS
       ppmhist	[-hexcolor  | -float | -colorname | -map] [-nomap] [-noheader]
       [-sort={frequency,rgb}] [ppmfile]


DESCRIPTION
       This program is part of Netpbm(1).

       ppmhistreads a PPM image as input and generates a histogram of the col-
       ors  in the image, i.e. a list of all the colors and how many pixels of
       each color are in the image.


   Output Format
       The output is in one of two basic formats:  a report for humans	and  a
       PPM  image  for use by programs.	 The PPM image is actually quite read-
       able by humans too.

       Human Report

       You get this format by specifying (or defaulting to) the -nomap option.

       The format is one line for each color in the input image.

       By default, there are two lines of column header at the top.   Use  the
       -noheader option to suppress those lines.

       In each line, ppmhist identifies the color by red, green, and blue com-
       ponents.	 By default, it lists each of  these  in  decimal,  using  the
       exact  values  that are in the PPM input.  So if the image has a maxval
       of 255, the numbers in the listing range from 0 to 255.	With the -hex-
       color  option,  you  can change these numbers to hexadecimal.  With the
       -float option, the numbers are fractional, adjusted to a maxval of 1.

       Each line lists the luminosity of the color.  It is in decimal  on  the
       same scale as the rgb values (see above).

       Each  line lists the number of pixels in the image that have the color.
       This is in decimal.


       PPM Output

       You get this format with the -map option.

       The output file is a genuine PPM image, but it is PPM Plain format  and
       contains	 comments  so  that  it	 is not a lot different from the human
       report described above.

       As a PPM image, it can be useful as input to other programs  that  need
       some  kind  of  palette.	 The image is a single row with one column for
       each distinct color in the image.



OPTIONS
       -sort={frequency,rgb}
	      The -sort option determines the order in which  the  colors  are
	      listed  in the output.  frequency means to list them in order of
	      how pixels in the input image have the color, with the most rep-
	      resented	colors	first.	 rgb  means  to sort them first by the
	      intensity of the red component of the color, then of the	green,
	      then of the blue, with the least intense first.

	      The default is frequency.


       -hexcolor
	      Print  the  color	 components in hexadecimal.  See output format
	      <#output> .

	      You may not specify this option along with -float or map.


       -float Print the color components and the luminosity as floating	 point
	      numbers in the range [0,1].  See output format <#output> .

	      You may not specify this option along with -hexcolor or map.

	      This option was added in Netpbm 10.19 (November 2003).


       -map   Generates	 a  PPM	 file  of the colormap for the image, with the
	      color histogram as comments.  See output format <#output> .

	      You may not specify this option along with -float or hexcolor.


       -nomap Generates the histogram for human reading.  This is the default.


       -colorname
	      Add the color name to the output.	 This is  the  name  from  the
	      system  color  dictionary	 <libppm.html#rgb.txt> .  If the exact
	      color is not in the color dictionary, it is  the	closest	 color
	      that  is	in  the	 dictionary  and is preceded by a '*'.	If you
	      don't have a system color dictionary, the program fails.

	      This option was added in Netpbm 10.10 (October 2002).


       -noheader
	      Do not print the column headings.




SEE ALSO
       ppm(1), pgmhist(1), pnmcolormmap(1), pnmhistmap(1), ppmchange(1)

AUTHOR
       Copyright (C) 1989 by Jef Poskanzer.



netpbm documentation		 24 June 2005		Ppmhist User Manual(0)