def METHOD_NAME(img):
    """
    If one of the inputs is a constant-value array, it will
    be normalized as an array of all zeros of the same shape.
    :param img: (CHANGE) (numpy.array): numpy array of phase image data.
    :return: numpy.array:image data with dtype float32.
    """
    img = img.astype('float32')
    sample_value = img[(0,) * img.ndim]
    if (img == sample_value).all():
        return np.zeros_like(img)
    img = rescale_intensity(img, out_range=(0.0, 1.0))
    return img