def add_indices(indices)
      raise ArgumentError, "Invalid argument 'indices'. Expected Array/NArray, got #{indices.class}." unless [NArray, Array].include?(indices.class)
      raise ArgumentError, "Invalid argument 'indices'. Expected Array to contain only integers, got #{indices.collect{|i| i.class}.uniq}." if indices.is_a?(Array) and not indices.collect{|i| i.class}.uniq == [Fixnum]
      indices = indices.to_a if indices.is_a?(NArray)
      @indices += indices
    end
def add_indices(indices)
      raise ArgumentError, "Invalid argument 'indices'. Expected Array/NArray, got #{indices.class}." unless [NArray, Array].include?(indices.class)
      raise ArgumentError, "Invalid argument 'indices'. Expected Array to contain only integers, got #{indices.collect{|i| i.class}.uniq}." if indices.is_a?(Array) and not indices.collect{|i| i.class}.uniq == [Fixnum]
      indices = indices.to_a if indices.is_a?(NArray)
      @indices += indices
    end
Adds an array of (general) indices to this Selection.

 @param [Array, NArray] indices general pixel indices to be added to the selection