def get_per_pixel_mean(self, names=('train', 'test')):
        """
        Args:
            names (tuple[str]): the names ('train' or 'test') of the datasets

        Returns:
            a mean image of all images in the given datasets, with size 32x32x3
        """
        for name in names:
            assert name in ['train', 'test'], name
        train_files, test_files, _ = get_filenames(self.dir, self.cifar_classnum)
        all_files = []
        if 'train' in names:
            all_files.extend(train_files)
        if 'test' in names:
            all_files.extend(test_files)
        all_imgs = [x[0] for x in read_cifar(all_files, self.cifar_classnum)]
        arr = np.array(all_imgs, dtype='float32')
        mean = np.mean(arr, axis=0)
        return mean

        Args:
            names (tuple[str]): the names ('train' or 'test') of the datasets

        Returns:
            a mean image of all images in the given datasets, with size 32x32x3
        
tensorpack/dataflow/dataset/cifar.py