y = (x - mean) / std
x = (y * std) + mean
Just do such an operation per-channel on your output:
# assuming x and y are Batch x 3 x H x W and mean = (0.4914, 0.4822, 0.4465), std = (0.2023, 0.1994, 0.2010)
x = y.new(*y.size())
x[:, 0, :, :] = y[:, 0, :, :] * std[0] + mean[0]
x[:, 1, :, :] = y[:, 1, :, :] * std[1] + mean[1]
x[:, 2, :, :] = y[:, 2, :, :] * std[2] + mean[2]