NAME

       pamrubber - a rubber-sheeting utility that stretches an image based on control points

SYNOPSIS

       pamrubber  {-tri  |  -quad}  [-linear] [-frame] [-randomseed=N] cp1x cp1y [cp2x cp2y [cp3x
       cp3y [cp4x cp4y]]] cp1x cp1y [cp2x cp2y [cp3x cp3y [cp4x cp4y]]] [filename]

       Minimum unique abbreviation of options is acceptable.  You may use double hyphens  instead
       of single hyphen to denote options.

DESCRIPTION

       This program is part of Netpbm(1).

       The  pamrubber  utility  converts  a  pam  image  into a new image with the contents moved
       around.  The transformation is often called "rubber sheeting": you identify control points
       (CP)  on  the  source  image  and specify new positions for those points in the new image.
       pamrubber moves all the pixels around, stretching and compressing as necessary, as if  the
       original  image  were on a sheet of rubber and you pulled on the sheet to make the control
       points move to their new locations.

       The new image has the same dimensions and format as the original.

       The transformation can happen in two very different ways, called "quad"  and  "tri."  With
       the  former, you must specify four control points (for both source and target).  These are
       the corners of two quadrilaterals that will act as the coordinate system for  both  source
       and  target images.  Consider them as non-orthogonal (0,0), (0,1), (1,0) and (1,1) points.
       This transformation comes close to the one pamperspective does, however that program  does
       other corrections as well.

       When  you  specify  less  than four control points, the program adds control points in the
       following way.  With three control points, pamrubber chooses the fourth one such that  the
       four  points form a parallelogram.  With two points, pamrubber considers them the opposite
       corners of a rectangle.  When you  specify  only  one  control  point,  pamrubber  uses  a
       rectangle from the top left corner of the image to the single control point.

       In  "tri" mode, pamrubber conceptually cuts up the source and target image into triangles.
       It Transforms within each corresponding pair of triangles in a stretching  fashion.   It's
       like pulling on the three corners of the triangle.  In this mode, each pixel in the source
       image gets mapped to a position in the target image. No pixels are lost.

       When, in "tri" mode, you specify only a single control point  in  the  source  and  target
       image,  pamrubber creates four triangles from this point to the four corners of the image.
       With two points, the program creates six triangles from the  two  endpoints  of  the  line
       connecting the two points, again to the four corners of the image. Three control points is
       in a way the core of this utility in "tri" mode.  Between the three edges of  the  central
       triangle  and  the  four edges of the image, pamrubber constructs another seven triangles.
       Four control points define two central connected triangles.   In  total  this  results  in
       cutting the source and target image up into ten triangles.

       In  this  case  clearly  a  picture says more than a thousand words.  There is a graphical
       illustration of these various modes at
        www.schaik.com/netpbm/rubber ⟨http://www.schaik.com/netpbm/rubber⟩ .  An example  of  how
       to use this type of rubber sheeting in cartography is in the article
        Visualizing           the          Landscape          of          Old-Time          Tokyo
       ⟨http://www.isprs.org/proceedings/XXXVI/5-W1/papers/21.pdf⟩ .

PARAMETERS

       The parameters are control points (cp) in pairs of x and y.  The source and  target  image
       must  have the same number of control points.  The minimum number of values specified here
       is 4 for a single control point in the source and target image.  The  maximum  is  16  for
       four control points in each image.

       filename  is  the  name  of the input file. If you don't specify this, pamrubber reads the
       image from Standard Input.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet,
       see
        Common  Options  ⟨index.html#commonoptions⟩ ), pamrubber recognizes the following command
       line options:

       -tri | -quad

              This selects the type of rubber sheeting done.  You must  specify  exactly  one  of
              these options.

       -linear

              This  determines  whether pamrubber uses nearest neighbor interpolation or bilinear
              interpolation of four source pixels.

       -frame

              This option causes pamrubber to overlay the target image  with  the  edges  of  the
              quadrilaterals,  respectively  the  triangles used for the rubber sheeting.  To get
              the same overlay  for  the  source  image,  use  a  pamrubber  transformation  with
              identical control points for source and target.

       -randomseed=N

              pamrubber  randomizes  some  of  its  output.   So  that you can produce repeatable
              results, you can choose the seed of the random number generator with  this  option.
              If  you  use  the  same  input image and the same random number generator seed, you
              should always get the exact same output.  By default, pamrubber uses  the  time  of
              day  as  the  seed,  so  you get slightly different output when you run the program
              twice on the same input.

              Before Netpbm 10.61 (December 2012), this was  called  -randseed,  and  that  still
              works.

SEE ALSO

       pam(1) and pamperspective(1)

HISTORY

       pamrubber was new in Netpbm 10.54 (March 2011).

AUTHORS

       Willem van Schaik wrote this program in February 2011 and contributed it to Netpbm.

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/pamrubber.html