pnmcrop man page

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 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 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 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 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 average 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 appropriate -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 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 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 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, including 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

Referenced By

pamcut(1), pbmtext(1), pbmtextps(1), pnmmargin(1), pnmpad(1).

31 December 2016 netpbm documentation