MNIST的均值和方差(0.1307,), (0.3081,)是怎么计算出来的？

不多说 上代码解释

self.train_x_set = self.train_x_set / 255.
mean = 0
std = 0
for x in self.train_x_set:
    mean += np.mean(x[0, :, :])
mean /= len(self.train_x_set)
self.train_x_set -= mean
for x in self.train_x_set:
    std += np.mean(np.square(x[0, :, :]).flatten())
std = np.sqrt(std / len(self.train_x_set))