def min_depth_img(self, num_img=1):
        """Collect a series of depth images and return the min of the set.

        Parameters
        ----------
        num_img : int
            The number of consecutive frames to process.

        Returns
        -------
        :obj:`DepthImage`
            The min DepthImage collected from the frames.
        """
        depths = self._read_depth_images(num_img)

        return Image.min_images(depths)