def dataset_norm(train, test):
    """
    Dataset normalization.
    Arguments:
        train (ndarray): Train data.
        test (ndarray): Test data.
    Return:
        train_norm, test_norm (tuple): Normelized images.
    """
    train_norm = train.astype('float32')
    test_norm = test.astype('float32')
    train_norm = train_norm / 255
    test_norm = test_norm / 255
    return train_norm, test_norm