This is where it becomes tricky. Describing the images I can definitely underline exactly what the function is supposed to do, but maybe the example is too simple: I chose mm space to be represented by `np.eye(4)`. The data are described by a different affine, from which I then transform to millimeter space using 3 different techniques. Can this cause a potential confusion between the target space of the transformation and millimeter space? This is my worry, but I am not entirely sure how to do this better.