pnmcrop(1) - phpMan

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 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).

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 output.

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 instead 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 borders 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 independently and pro-
duces 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 ignored
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 pam-
comp.

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 corners 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, pnmcrop 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, bottom. If all four corners are different colors, pnmcrop assumes an aver-
age of the four colors as the background color.

The -sides option slows pnmcrop down, as it reads the entire image 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 operative 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. pnmcrop will
choose some particular shade as the background color and if you specify an appro-
priate -closeness value, it will correctly 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 figures out what part of
the image is border and what part is foreground (not border), as well as the back-
ground 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 borders, 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 con-
clusion as to where the borders are and what the background color is by preprocess-
ing 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 deter-
mines 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, including exactly how
much is being cropped off of which sides.