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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 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 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 unreadably 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 particularly elegant solution to the problem.
SEE ALSO
pgmhist(1), ppmhist(1), pgm(1), ppm(1)
AUTHOR
Wilson H. Bent. Jr. (whb AT 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(0)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
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