code: def _write_png(tmp_path, xdim, ydim):
      dtype = np.uint8
      a = np.zeros((xdim, ydim), dtype=dtype)
      f = str(tmp_path / "temp.png")
      im = Image.fromarray(a, "L")
      im.save(f)
  
imports: import sys
  import pytest
  from PIL import Image
label_desc: Use image node_id 1 for calling a global function with example usage: _write_png(tmp_path, xdim, ydim) without return types