Because it's Perl, I think I may try another shot (semi-golf version):

 use Imager;
 my ($n, $fac) = (40, 10);               # 2D-SIZE, FACTOR TO IMAGE
 my $fn = shift || 'datafile.dat';       
 open my $fh, '<', $fn or die "$fn $!";  # OPEN FILE
 my $img = Imager->new(xsize=>$n*$fac, ysize=>$n*$fac, channels=>3);
 $img->box(filled=>1, color=>'#FFFFFF'); # BACKGROUND
 $img->box(color=>[($_->[2]/10)*25, $_->[2]*2.5, $_->[2] ], filled=>1,
           xmax=>($_->[0]+1)*$fac, ymax=>($_->[1]+1)*$fac,
           xmin=>$_->[0]*$fac, ymin=>$_->[1]*$fac) for map [split /\s+
+/], <$fh>;
 $img->write(file=>'my.jpg', jpegquality=>90) or die $img->errstr;
[download]

the 2D matrix storage is't really necessary, this can be handled in "mid-air" ...

Regards

mwa