1、Scipy计算SNR,正式版本中已删除，原定义如下：

    1. def signaltonoise(a, axis=0, ddof=0):
    2.     """
    3.     The signal-to-noise ratio of the input data.
    4.     Returns the signal-to-noise ratio of `a`, here defined as the mean
    5.     divided by the standard deviation.
    6.     Parameters
    7.     ----------
    8.     a : array_like
    9.         An array_like object containing the sample data.
    10.     axis : int or None, optional
    11.         Axis along which to operate. Default is 0. If None, compute over
    12.         the whole array `a`.
    13.     ddof : int, optional
    14.         Degrees of freedom correction for standard deviation. Default is 0.
    15.     Returns
    16.     -------
    17.     s2n : ndarray
    18.         The mean to standard deviation ratio(s) along `axis`, or 0 where the
    19.         standard deviation is 0.
    20.     """
    21.     a = np.asanyarray(a)
    22.     m = a.mean(axis)
    23.     sd = a.std(axis=axis, ddof=ddof)
    24.     return np.where(sd == 0, 0, m/sd)

    2、Dipy提供了SNR的计算

    https://github.com/scipy/scipy/blob/v0.16.0/scipy/stats/stats.py#L1963