class_docstr: Synthetic dataset class. Mean image is returned always. This dataset
  is used/recommended to use for testing purposes only.
  
  Args:
      path (string): can be "" [not used]
      split (string): specify split for the dataset.
          Usually train/val/test. Used to read images if
          reading from a folder `path' and retrieve settings for that split
          from the config path [not used]
      dataset_name (string): name of dataset. For information only. [not used]
      data_source (string, Optional): data source ("synthetic") [not used]
docstr: Size of the dataset
docstr_tok: ["Size","of","the","dataset"]
code: def num_samples(self):
      """
      Size of the dataset
      """
      return self._num_samples
  
file_path: vissl/vissl/data/synthetic_dataset.py
imports: from typing import List
  import numpy
  from PIL import Image, ImageFilter
  from torch.utils.data import Dataset
  from vissl.data.data_helper import get_mean_image
label_desc: Use image node_id 2 for calling the SyntheticImageDataset obj's underlying member method code with example usage: obj.num_samples() and returns: self