Query: downsampling 2d python array

Relevant code:
def downsample_with_striding(array, factor):
    """Downsample x by factor using striding.

    @return: The downsampled array, of the same type as x.
    """
    return array[tuple(np.s_[::f] for f in factor)]

Similar but not relevant code:
def convolve_fft(array, kernel):
    """
    Convolve an array with a kernel using FFT.
    Implemntation based on the convolve_fft function from astropy.

    https://github.com/astropy/astropy/blob/master/astropy/convolution/convolve.py
    """

    array = np.asarray(array, dtype=np.complex)
    kernel = np.asarray(kernel, dtype=np.complex)

    if array.ndim != kernel.ndim:
        raise ValueError("Image and kernel must have same number of "
                         "dimensions")

    array_shape = array.shape
    kernel_shape = kernel.shape
    new_shape = np.array(array_shape) + np.array(kernel_shape)

    array_slices = []
    kernel_slices = []
    for (new_dimsize, array_dimsize, kernel_dimsize) in zip(
            new_shape, array_shape, kernel_shape):
        center = new_dimsize - (new_dimsize + 1) // 2
        array_slices += [slice(center - array_dimsize // 2,
                         center + (array_dimsize + 1) // 2)]
        kernel_slices += [slice(center - kernel_dimsize // 2,
                          center + (kernel_dimsize + 1) // 2)]

    array_slices = tuple(array_slices)
    kernel_slices = tuple(kernel_slices)

    if not np.all(new_shape == array_shape):
        big_array = np.zeros(new_shape, dtype=np.complex)
        big_array[array_slices] = array
    else:
        big_array = array

    if not np.all(new_shape == kernel_shape):
        big_kernel = np.zeros(new_shape, dtype=np.complex)
        big_kernel[kernel_slices] = kernel
    else:
        big_kernel = kernel

    array_fft = np.fft.fftn(big_array)
    kernel_fft = np.fft.fftn(np.fft.ifftshift(big_kernel))

    rifft = np.fft.ifftn(array_fft * kernel_fft)

    return rifft[array_slices].real

Similar but not relevant code:
def pad_image(arr, max_size=400):
    """Pads an image to a square then resamples to max_size"""
    dim = np.max(arr.shape)
    img = np.zeros((dim, dim, 3), dtype=arr.dtype)
    xl = (dim - arr.shape[0]) // 2
    yl = (dim - arr.shape[1]) // 2
    img[xl:arr.shape[0]+xl, yl:arr.shape[1]+yl, :] = arr
    return resample_image(img, max_size=max_size)

Similar but not relevant code:
def resample(grid, wl, flux):
    """ Resample spectrum onto desired grid """
    flux_rs = (interpolate.interp1d(wl, flux))(grid)
    return flux_rs

Similar but not relevant code:
def denorm(self,arr):
        """Reverse the normalization done to a batch of images.

        Arguments:
            arr: of shape/size (N,3,sz,sz)
        """
        if type(arr) is not np.ndarray: arr = to_np(arr)
        if len(arr.shape)==3: arr = arr[None]
        return self.transform.denorm(np.rollaxis(arr,1,4))

Similar but not relevant code:
def _rescale_array(self, array, scale, zero):
        """
        Scale the input array
        """
        if scale != 1.0:
            sval = numpy.array(scale, dtype=array.dtype)
            array *= sval
        if zero != 0.0:
            zval = numpy.array(zero, dtype=array.dtype)
            array += zval