### The Blue Dither algorithm itself (acting on RGBA values of the pixels)
use 'GFX-Tools-Buffer::matrix'; ### uses this math matrix class !
sub new {
    my $class = shift;
    $self = { percentage => 0.1, }; ### amount of dither 
    bless $self, $class;
}
sub setPercentage {
  my ($self, $p) = @_;
  $self->{percentage} = $p;
}
sub ditherBlue {
  my ($self, $matrixbitmapobj) = @_;
  my $matrix = $matrixbitmapobj->getMatrix;
   
  my $pngbppmultiplynumber = 4 - 1; ### R,G,B and A
     
  for (my $j = 0; $j < $matrix->getRowsNumber * $pngbppmultiplynumber; $j++) {
    for (my $i = 0; $i < $matrix->getColumnsNumber; $i++) {
      for (my $rgbanumber = $pngbppmultiplynumber; $rgbanumber >= 0; $rgbanumber--) {
        if ($rgbanumber == 2) { ### choose blue in the matrix
          $matrix->setAtIndex($j, $i, hex(floor($matrix->indexOf($j,$i) * $self->{percentage})));
        }
      }
    }
  } 
  ### NOTE : returns a class
  return MatrixBitmap->new->setMatrix($matrix);
}
1;