sub palette_rgb_gd {
   my $abs_path = _abs_path($_[0]) or return;
   
   my @colors;


   require GD;
   my $img = GD::Image->new( $abs_path ) or die $!;

   my $colors = $img->colorsTotal
       or carp("$abs_path is a truecolor image (no palette)?");

   for ( 0 .. $colors ) {
      my $rgb = sprintf '%02x%02x%02x', $img->rgb( $_ );
      #debug( $rgb);
      #printf "%5d: R:%2x G:%2x B:%2x\n", $_, $img->rgb( $_ );
      push @colors , $rgb;
   }      
   return @colors;
}