Ppmhist User Manual(1) General Commands Manual Ppmhist User Manual(1)
NAME
ppmhist - print a histogram of the colors in a PPM image
SYNOPSIS
ppmhist [-hexcolor | -float | -colorname | -map] [-nomap] [-noheader]
[-sort={frequency,rgb}] [-forensic] [ppmfile]
DESCRIPTION
This program is part of Netpbm(1).
ppmhist reads a PPM image as input and generates a histogram of the
colors 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 and a summary at the
top. Use the -noheader option to suppress those lines.
The summary tells you whether black or white are present and how many
shades of gray and color are present. The summary was new in Netpbm
10.82 (March 2018).
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 ex-
act 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 re-
port 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.
The function of PPM output is essentially the same as the output of pn-
mcolormap all. ppmhist is much older than pnmcolormap.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), ppmhist recognizes the
following command line options:
-sort={frequency,rgb}
The -sort option determines the order in which the colors are
listed in the output. rgb means to sort them first by the in-
tensity of the red component of the color, then of the green,
then of the blue, with the least intense first. frequency means
to list them in order of how many pixels in the input image have
the color, with the most represented colors first. Among colors
with the same frequency, the order is the same as with rgb.
The default is frequency.
Before Netpbm 10.88 (September 2019), with -sort=frequency, the
order of colors that have the same frequency is arbitrary.
-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#dictionary⟩ . 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.
-forensic
With this option, ppmhist works on images that contain invalid
sample values. Normally, like most Netpbm programs, ppmhist
fails if it encounters a sample value greater than the maxval
that the image declares. The presence of such a value means the
image is invalid, so the pixels have no meaning. But with
-forensic, ppmhist produces a histogram of the actual sample
values without regard to maxval. It issues messages summarizing
the invalid pixels if there are any.
One use for this is to diagnose the problem that caused the in-
valid Netpbm image to exist.
There is a small exception to the ability of ppmhist to process
invalid pixels even with -forensic: it can never process a sam-
ple value greater than 65535. Note that in the rarely used
Plain PPM format, it is possible for a number greater than that
to appear where a sample value belongs.
This option was new in Netpbm 10.66 (March 2014). But Netpbm
older than 10.66 does not properly reject invalid sample values,
so the effect is very similar to -forensic.
SEE ALSO
ppm(1), pgmhist(1), pnmcolormap(1), pnmhistmap(1), ppmchange(1)
AUTHOR
Copyright (C) 1989 by Jef Poskanzer.
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/ppmhist.html
netpbm documentation 24 August 2019 Ppmhist User Manual(1)
Generated by dwww version 1.15 on Sat Jun 29 02:01:22 CEST 2024.