Pnmhistmap User Manual(1) General Commands Manual Pnmhistmap User Manual(1)
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 re-
sults 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 ]8;;index.html#commonoptions\ Common Options]8;;\ ), 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 in-
tensity 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 his-
togram data to become unreadably small. Note that, for color in-
puts, these options apply to all colors; if, for example, the in-
put 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 sin-
gle-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 scal-
ing 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)
Generated by dwww version 1.16 on Tue Dec 16 04:47:34 CET 2025.