code: def get_alpha(img):
      return 0.5 * np.arange(img.size).reshape(img.shape) / img.size
  
file_path: MONAI/tests/test_blend_images.py
imports: from __future__ import annotations
  import unittest
  from unittest.case import skipUnless
  import numpy
  import torch
  from parameterized import parameterized
  from monai.data.synthetic import create_test_image_2d, create_test_image_3d
  from monai.transforms.utils_pytorch_numpy_unification import moveaxis
  from monai.utils.module import optional_import
  from monai.visualize.utils import blend_images
  from tests.utils import TEST_NDARRAYS
label_desc: Use image node_id 1 for calling a global function with example usage: get_alpha(img) and returns: unknown