Provided by: netpbm_11.01.00-2build1_amd64 bug

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 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.

       But note that pnmcrop's determination of the background  color  is  independent  of  which
       edges  you  crop,  which  may not be intuitive.  For example, 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
       anything, 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  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

       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 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.

              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 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.

              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 default), 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 consistent
                      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 remains.
                    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 image, this
                    selects a cropping of 600 pixels from the left and none from the other
                    three sides.  Note that were this cropping actually applied, 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.  Instead, it just prints
              to  Standard Output parameters of the cropping 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, 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