A parallel version for the updated code in the first post. Workers must be spawned prior to creating the image. Otherwise, Perl will crash from the Imager module not thread safe. This is also the case for the GD module.

use strict;
use warnings;
use Imager;
use MCE;

# based on original http://www.alfrog.com/mandel.html
# karlgoethebier: code refactor
# marioroy: parallelization

my $width      = 1280;
my $height     = 1024;
my $iterations = 20;
my @palette;
my $image;

my $mce = MCE->new(
   use_threads => 0,  # MCE defaults to threads on windows
   max_workers => 'auto',
   chunk_size  => 8,

   gather => sub {
      my ( $x, $y, $color );
      while ( ($x, $y, $color) = splice(@_, 0, 3) ) {
         $image->setpixel( x => $x, y => $y, color => $palette[$color]
+ );
      }
   },

   user_func => sub {
      my ( $mce, $chunk_ref, $chunk_id ) = @_;
      my ( $re_c, $im_c, $re_z, $im_z, $color, $temp );
      my ( @set_data );

      for my $x ( $chunk_ref->[0] .. $chunk_ref->[1] ) {
         for my $y ( 0 .. $height - 1 ) {
            $re_c = ( $x - 3 * $width / 4 ) / ( $width / 3 );
            $im_c = ( $y - $height / 2 ) / ( $width / 3 );
            $re_z = $im_z = $color = 0;

            while ( 1 ) {
               $temp = $re_z;
               $re_z = $re_z * $re_z - $im_z * $im_z + $re_c;
               $im_z = 2 * $temp * $im_z + $im_c;
               ++$color;

               last if $re_z * $re_z + $im_z * $im_z > 4;

               if ( $color == $iterations ) {
                  $color = 0;
                  last;
               }
            }

            push @set_data, $x, $y, $color;
         }
      }

      MCE->gather( @set_data );
   }
);

# spawn MCE workers
$mce->spawn;

# init image and color palette
$image = Imager->new( xsize => $width, ysize => $height );
push @palette, Imager::Color->new( 0, 0, 0 ); # black

for ( 1 .. $iterations ) {
   my ( $r, $g, $b ) = map { int rand 255 } 1 .. 3;
   push @palette, Imager::Color->new( $r, $g, $b );
}

# compute mandelbrot
$mce->process({ bounds_only => 1, sequence => [ 0, $width - 1 ] });
$mce->shutdown;

# save image
my $file = qq(mandelbrot.png);
$image->write( file => $file );
[download]

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