def image_surface(nb_points):
    """ generate surface from data """
    from skimage import data
    from skimage.util import img_as_float
    from skimage.transform import rescale, resize
    from skimage.color import rgb2gray
    shape = nb_points, nb_points
    image = img_as_float(resize(rgb2gray(data.astronaut()), shape))
    print(image.shape)
    print(type(image))
    return image
