As Chart::Plot is still rather simple I think you will need to graph then modify the image, but fortunately that is rather easy to do as you have complete access to the underlying GD object. Of course this will work just fine in Win32 (that's where I tested it).

There is one more glitch however - Chart::Plot does not correctly account for the plotting offset caused by insertion of the graph title, so you cannot use that option if you want this to work. You may just superimpose the graph title text via the GD object, I didn't bother for this trial. I hope this helps!

#!/usr/bin/perl -w

use strict;
use Chart::Plot;

my $img = Chart::Plot->new();

my @xdataset = qw(791.312 809.298 825.259 842.510 855.028 861.120 
                  870.554 870.977 877.036 893.436 1060.006 1066.030 
                  1081.967 1270.989 2211.105 2225.178 2239.090);
my @ydataset = qw(1383.8 1863.9 1247   2191.4 2101.2 624.96 
                  552.55 1050.3 690.71 538.11 705.84 566.41 
                  397.68 133.13 158.5 91.587 82.42);

$img->setGraphOptions (
                       'horGraphOffset' => 75,
                       'vertGraphOffset' => 100,
                       'horAxisLabel' => 'mass/charge',
                       'vertAxisLabel' => 'intensity',
                      );

# plots nothing visible, but sets up axis scales:
$img->setData (\@xdataset, \@ydataset,  'nolines nopoints');

# now draw some vertical bars:
my $gdobj = $img->getGDobject;
my $blue = $gdobj->colorAllocate(0,0,255);
for my $i (0..$#xdataset) {
  $gdobj->line($img->data2pxl($xdataset[$i],0),
               $img->data2pxl($xdataset[$i], $ydataset[$i]),
               $blue);
}

open (WR,'>plot.png') or die ("Failed to write file: $!");
binmode WR;            # for DOSish platforms
print WR $img->draw();
close WR;
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I'd like to be able to assign to an luser