Pnmcrop User Manual(1) General Commands Manual Pnmcrop User Manual(1)
NAME
pnmcrop - crop a Netpbm image
SYNOPSIS
pnmcrop
[-white |-black |-sides |-bg-color=color |-bg-corner={
topleft|topright|bottomleft|bottomright} ]
[-left]
[-right]
[-top]
[-bottom]
[-margin=pixels]
[-closeness=closeness_percent]
[-borderfile=filename]
[-blank-image={abort|pass|minimize|maxcrop}]
{[-reportfull]|[-reportsize]}
[-verbose]
[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.
But note that pnmcrop's determination of the background color is inde-
pendent of which edges you crop, which may not be intuitive. For exam-
ple, imagine an image with a blue border at the top and a black border
at the bottom and you say to crop the bottom (-bottom). You may have
expected to crop the black border, but you actually won't crop any-
thing, because pnmcrop considers the background color to be whatever
color the top two corners are, which is blue, and there is no blue at
the bottom of the image. If you do want pnmcrop to take the background
color from the edges being cropped, use -bg-corner.
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
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see
Common Options ⟨index.html#commonoptions⟩ ), pnmcrop recognizes the
following command line options:
-white Take white to be the background color. pnmcrop removes borders
which are white.
You may specify at most one of -black, -white, -sides, -bg-
color, and -bg-corner.
-black Take black to be the background color. pnmcrop removes borders
which are black.
You may specify at most one of -black, -white, -sides, -bg-
color, and -bg-corner.
-bg-color=color
This tells pnmcrop what color is the background - it will crop
areas of this color. color is a value that would be used as the
argument of the pnm_parsecolor() library routine
⟨libnetpbm_image.html#colorname⟩ .
You may specify at most one of -black, -white, -sides, -bg-
color, and -bg-corner.
This option was new in Netpbm 10.86 (March 2019).
-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.
You may specify at most one of -black, -white, -sides, -bg-
color, and -bg-corner.
-bg-corner={topleft|topright|bottomleft|bottomright
This option indicates a corner which is background. pnmcrop
will use the color of this corner as the background color and
crop edges of that color.
You may specify at most one of -black, -white, -sides, -bg-
color, and -bg-corner.
This option was new in Netpbm 10.86 (March 2019).
-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.
The border file must have the same number of images in it as the
input file; the background color determination for image N of
the input is based on the image N of the border file.
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).
-blank-image={abort|pass|minimize|maxcrop}
This determines how pnmcrop handles an image which is entirely
background (blank), a case where cropping doesn't make much
sense.
abort
program fails, with explanatory message (default)
pass
Output image is the same as the input image.
-margin has no effect.
minimize
output is a single row, column, or pixel (of the background
color).
If you crop both vertically and horizontally (the de-
fault), it is a
single pixel. If you crop only vertically, a single row,
of the
original width. If you crop only horizontally, it is a
single column,
of the original height.
This is a somewhat incongruous result; the mathematically con-
sistent
result of cropping the background from an image that is
entirely
background would be an image with no pixels at all. But
such a thing
does not exist in the Netpbm formats (and you probably
wouldn't want
it anyway, because whoever processes this output may not
tolerate
that).
The background can be more than one color when you specify
-closeness, so it matters which row, column, or pixel re-
mains.
If you crop on the top and not bottom, it is the last row
that remains.
If you crop on both the top and bottom, it is the middle
row that
remains. The other cases follow similarly.
If you specify a margin (-margin), the output image consists
entirely of the margins; there is no single row, column,
or pixel
between the margins. So with -margin, the incongruity
mentioned above does not exist. But before Netpbm 10.92
(September
2020), -margin was ignored with -blank-image=minimize.
maxcrop
This odd function selects a hypothetical cropping which is not
even
possible, and therefore is valid only with -reportfull or
-reportsize. The cropping that this selects is a crop of
the
entire image on every side on which you request cropping.
So if you
request cropping only on the left, of a 600 pixel wide im-
age, this
selects a cropping of 600 pixels from the left and none
from the other
three sides. Note that were this cropping actually ap-
plied, this would
produce an image with no pixels, which is not a valid
Netpbm image. But
it gets stranger still if you request cropping on both the
right and the
left. In that case, the cropping selected is a cropping
of 600 pixels
from both the right and left sides, which would leave a
negative-width
image.
This is actually useful if you are trying to find a single
set of
cropping parameters to crop a stream of images. To do
this, you could
do a pass with -reportsize and -blank-image=maxcrop to
compute the maximum crop for each edge, and then use those
numbers in
-cropxxx options on a pamcut pass to do the crop.
In this scenario, any all-background (blank) images would
have no effect
on the cropping parameters you compute. If you do this,
you must give
special consideration to a stream with nothing but blank
images.
-margin is always ignored when the image is all background.
This option was new in Netpbm 10.86 (March 2019).
-reportfull
With this option, pnmcrop does not actually crop anything. In-
stead, it just prints to Standard Output parameters of the crop-
ping it would have done. The output is a single line per image,
like in this example:
0 +7 -20 -10 200 300 rgb-255:10/0/255 0.0
The line is composed of the following blank-delimited tokens:
• how many pixels would be cropped or padded on the left. This is
a signed decimal number, where + means pad and - means crop.
If there
would be no change, this is unsigned zero.
• same, but for the right side.
• same, but for the top.
• same, but for the bottom.
• the resulting image width in pixels, in decimal.
• the resulting image height in pixels, in decimal.
• The color pnmcrop took to be the background color, like
'rgb-255:10/0/255' (This is a format recognized by
the pnm_parsecolor() ⟨libnetpbm_image.html#colorname⟩
library routine). The maxval in the color specification is
the maxval of
the image.
• The closeness value (see -closeness option) pnmcrop
used, in floating point decimal.
You cannot use -borderfile together with this option.
This option was new in Netpbm 10.86 (March 2019).
-reportsize
This is like -reportfull, but reports only the left, right, top,
bottom, width, and height.
You cannot use -borderfile together with this option.
This option was new in Netpbm 10.86 (March 2019).
-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(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/pnmcrop.html
netpbm documentation 16 August 2020 Pnmcrop User Manual(1)
Generated by dwww version 1.15 on Sat Jun 29 02:22:10 CEST 2024.