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Pnmcrop User Manual(0) Pnmcrop User Manual(0)
NAME
pnmcrop - crop a Netpbm image
SYNOPSIS
pnmcrop
[-white|-black|-sides]
[-left]
[-right]
[-top]
[-bottom]
[-verbose]
[-margin=pixels]
[-closeness=closeness_percent]
[-borderfile=filename]
[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).
pnmcrop reads a PBM, PGM, or PPM image as input, removes borders that
are the background color, and produces the same type of image as out-
put.
If you don't specify otherwise, pnmcrop assumes the background color is
whatever color the top left and right corners of the image are and if
they are different colors, something midway between them. You can
specify that the background is white or black with the -white and
-black options or make pnmcrop base its guess on all four corners in-
stead of just two with -sides.
By default, pnmcrop chops off any stripe of background color it finds,
on all four sides. You can tell pnmcrop to remove only specific bor-
ders with the -left, -right, -top, and -bottom options.
If you want to leave some border, use the -margin option. It will not
only spare some of the border from cropping, but will fill in (with
what pnmcrop considers the background color) if necessary to get up to
that size.
If the input is a multi-image stream, pnmcrop processes each one inde-
pendently and produces a multi-image stream as output. It chooses
where to crop independently for each image. So if you start with a
stream of images of the same dimensions, you may end up with images of
differing dimensions. Before Netpbm 10.37 (December 2006), pnmcrop ig-
nored all input images but the first.
If you want to chop a specific amount off the side of an image, use
pamcut.
If you want to add different borders after removing the existing ones,
use pnmcat or pamcomp.
OPTIONS
-white Take white to be the background color. pnmcrop removes borders
which are white.
-black Take black to be the background color. pnmcrop removes borders
which are black.
-sides Determine the background color from the colors of the four cor-
ners of the input image. pnmcrop removes borders which are of
the background color.
If at least three of the four corners are the same color, pnm-
crop takes that as the background color. If not, pnmcrop looks
for two corners of the same color in the following order, taking
the first found as the background color: top, left, right, bot-
tom. If all four corners are different colors, pnmcrop assumes
an average of the four colors as the background color.
The -sides option slows pnmcrop down, as it reads the entire im-
age to determine the background color in addition to the up to
three times that it would read it without -sides.
-left Remove any left border.
-right Remove any right border.
-top Remove any top border.
-bottom
Remove any bottom border.
-margin=pixels
Leave pixels pixels of border. Expand the border to this size
if necessary.
This option was new in Netpbm 10.29 (August 2005).
-closeness=closeness_percent
Any color in the image that is at least this close to the opera-
tive background color is considered to be background.
You can use this if the image has borders that vary slightly in
color, such as would be the case in a photograph. Consider a
photograph against a white screen. The color of the screen
varies slightly with shading and dirt and such, but is still
quite distinct in color from the subject of the photograph. pn-
mcrop will choose some particular shade as the background color
and if you specify an appropriate -closeness value, it will cor-
rectly identify all of the screen as background and crop it off.
To implement more complex rules for identifying background, use
-borderfile.
The default is zero, which means a pixel's color must exactly
match the background color for the pixel to be considered part
of a background border.
This option was new in Netpbm 10.78 (March 2017). With older
Netpbm, colors must match exactly.
-borderfile=filename
Use the image in the file named filename instead of the input
image to determine where the borders of the input image are and
the background color.
Without this option, pnmcrop examines the input image and fig-
ures out what part of the image is border and what part is fore-
ground (not border), as well as the background color. With this
option, pnmcrop finds the borders in one image, then uses the
those four border sizes (left, right, top, bottom) in cropping a
different image. Furthermore, if you use -margin to add bor-
ders, the color of those borders is the background color pnmcrop
detects in the border file.
The point of this is that you may want to help pnmcrop to come
to a different conclusion as to where the borders are and what
the background color is by preprocessing the input image. For
example, consider an image that has speckles of noise in its
borders. pnmcrop isn't smart enough to recognize these as
noise; it sees them as foreground image. So pnmcrop considers
most of your borders to be foreground and does not crop them off
as you want. To fix this, run the image through a despeckler
such as pbmclean and tell pnmcrop to use the despeckled version
of the image as the -borderfile image, but the original speckled
version as the input image. That way, you crop the borders, but
retain the true foreground image, speckles and all.
This option was new in Netpbm 10.29 (August 2005).
Before Netpbm 10.46 (March 2009), the original image and not the
border file determines the background color. pnmcrop fails if
there is no apparent background color in the original image
(i.e. the corners of the image don't have a common color).
-verbose
Print on Standard Error information about the processing, in-
cluding exactly how much is being cropped off of which sides.
SEE ALSO
pamcut(1), pamfile(1), pnm(5)
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/pnmcrop.html
netpbm documentation 31 December 2016 Pnmcrop User Manual(0)
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