this is a simple "rescale to 256x256" program. (there are too many "use" statements here - this was cut from a larger program).

#! /bin/perl
use PDL;
use PDL::FFT;
use PDL::IO::Pic;
use PDL::Image2D;
use PDL::ImageRGB;
use PDL::ImageND;
use PDL::Primitive;
use PDL::Slices;

  $real = PDL->rpic('image.pgm');    # read image
  $display = zeroes(256,256);        # new empty image
  PDL::rescale2d($real, $display);   # scale into empty image
  $display->wpic("test.tif");       # done
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update:Zaxo: PDL::IO::Pic takes care of image headers, compression, etc. for you.