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: Simply return the mean dummy image of the specified size and mark
  it as a success.
docstr_tok: ["Simply","return","the","mean","dummy","image","of","the","specified","size","and","mark","it","as","a","success","."]
code: def __getitem__(self, idx: int):
      """
      Simply return the mean dummy image of the specified size and mark
      it as a success.
      """
      crop_size = self.cfg["DATA"][self.split].DEFAULT_GRAY_IMG_SIZE
      if self.cfg["DATA"][self.split].RANDOM_SYNTHETIC_IMAGES:
          img = self.generate_image(seed=idx, crop_size=crop_size)
      else:
          img = get_mean_image(crop_size)
      is_success = True
      return img, is_success
  
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 4 for calling the SyntheticImageDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: img,  is_success