def b_with_decompose
      if typecode == OBJECT or is_a?(Variable) or Thread.current[:lazy]
        b_without_decompose
      elsif typecode < RGB_
        decompose 2
      else
        self
      end
    end
def b_with_decompose
      if typecode == OBJECT or is_a?(Variable) or Thread.current[:lazy]
        b_without_decompose
      elsif typecode < RGB_
        decompose 2
      else
        self
      end
    end
Fast extraction for blue channel of RGB array

 @return [Node] Array with blue channel.