def column(x)
      assert_x!(x)
      (0...height).inject([]) { |pixels, y| pixels << get_pixel(x, y) }
    end
def column(x)
      assert_x!(x)
      (0...height).inject([]) { |pixels, y| pixels << get_pixel(x, y) }
    end
Returns an extracted column as vector of pixels.
 @param [Integer] x The 0-based column index.
 @return [Array<Integer>] The vector of pixels in the requested column.