code: def test_png(db):
      studies = dft.get_studies(data_dir)
      data = studies[0].series[0].as_png()
      im = PImage.open(BytesIO(data))
      assert im.size == (256, 256)
  
imports: import os
  import sqlite3
  from io import BytesIO
  from os.path import dirname
  from os.path import join
  from ..testing import suppress_warnings
  import unittest
  import pytest
  from ..None import nifti1
  from ..optpkg import optional_package
label_desc: Use image node_id 7 for calling a global function with example usage: test_png(db) without return types