NAME

       pamstretch - scale up a PNM or PAM image by interpolating between pixels.

SYNOPSIS

       pamstretch

       [-xscale=X]

       [-yscale=Y] [-blackedge]

       [-dropedge]

       N

       [infile]

       You  can  use  the  minimum  unique  abbreviation of the options.  You can use two hyphens
       instead of one.  You can separate an option name from its value with white  space  instead
       of an equals sign.

DESCRIPTION

       This program is part of Netpbm(1).

       pamstretch   scales  up  pictures  by  integer values, either vertically, horizontally, or
       both.  pamstretch  differs from pamscale and  pamenlarge  in  that  when  it  inserts  the
       additional  rows  and  columns,  instead  of  making  the  new row or column a copy of its
       neighbor, pamstretch makes the new row or column an interpolation between  its  neighbors.
       In some images, this produces better looking output.

       To scale up to non-integer pixel sizes, e.g. 2.5, try pamstretch-gen(1) instead.

       Options  let  you select alternative methods of dealing with the right/bottom edges of the
       picture.  Since the interpolation is done between the top-left corners  of  the  scaled-up
       pixels, it's not obvious what to do with the right/bottom edges.  The default behaviour is
       to scale  those  up  without  interpolation  (more  precisely,  the  right  edge  is  only
       interpolated vertically, and the bottom edge is only interpolated horizontally), but there
       are two other possibilities, selected by the -blackedge and -dropedge options.

       In the special case that the stretch factor is 1, there is no issue  with  the  right  and
       bottom  edges,  the edges of the output are identical to the edges of the input regardless
       of -blackedge and -dropedge.  However, before Netpbm 10.86 (March 2019),  -dropedge  would
       cause the edge to be dropped even where the stretch factor was 1.

PARAMETERS

       The  N  parameter  is  the scale factor.  It is valid only if you don't specify -xscale or
       -yscale.  In that case, pamstretch scales in both dimensions and by the scale factor N.

       Before Netpbm 10.86 (March 2019), 1 was not a valid value.

OPTIONS

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

       -xscale=X
              This is the horizontal scale factor.  If you don't specify this, but do  specify  a
              vertical scale factor, the horizontal scale factor is 1.

              This option was new in Netpbm 9.21 (December 2001).

       -yscale=Y
              This  is  the  vertical  scale factor.  If you don't specify this, but do specify a
              horizontal scale factor, the vertical scale factor is 1.

              This option was new in Netpbm 9.21 (December 2001).

       -blackedge
              interpolate to black at right/bottom edges.

       -dropedge
              drop one (source) pixel at right/bottom edges. This is arguably more  logical  than
              the default behaviour, but it means producing output which is a slightly odd size.

LIMITATIONS

       Usually  produces  fairly ugly output for PBMs. For most PBM input you'll probably want to
       reduce the `noise' first using something like pnmnlfilt(1).

SEE ALSO

       pamstretch-gen(1), pamenlarge(1), pamscale(1), pnmnlfilt(1)

AUTHOR

       Russell Marks (russell.marks@ntlworld.com).

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/pamstretch.html