code: def test_sgnd(tmp_path):
      outfile = str(tmp_path / "temp.jp2")
  
      im = Image.new("L", (1, 1))
      im.save(outfile)
      with Image.open(outfile) as reloaded:
          assert reloaded.getpixel((0, 0)) == 0
  
      im = Image.new("L", (1, 1))
      im.save(outfile, signed=True)
      with Image.open(outfile) as reloaded_signed:
          assert reloaded_signed.getpixel((0, 0)) == 128
  
imports: from __future__ import annotations
  import os
  import re
  from io import BytesIO
  import pytest
  from PIL import Image, ImageFile, Jpeg2KImagePlugin, UnidentifiedImageError, _binary, features
  from .helper import assert_image_equal, assert_image_similar, assert_image_similar_tofile, skip_unless_feature, skip_unless_feature_version
label_desc: Use image node_id 25 for calling a global function with example usage: test_sgnd(tmp_path) without return types