def blurring_kernel(shape=None):
    """Blurring kernel for convolution simulations.

    The kernel is scaled to sum to one.

    Returns
    -------
    An image with the following properties:
        image type: gray scales
        size: [100, 100] (if not specified by `size`)
        scale: [0, 1]
        type: float64

    """
    # TODO: Store data in some ODL controlled url
    name = 'motionblur.mat'
    url = URL_CAM + name
    dct = get_data(name, subset=DATA_SUBSET, url=url)

    return convert(255 - dct['im'], shape, normalize='sum')
Blurring kernel for convolution simulations.

    The kernel is scaled to sum to one.

    Returns
    -------
    An image with the following properties:
        image type: gray scales
        size: [100, 100] (if not specified by `size`)
        scale: [0, 1]
        type: float64