code: def test_png_bitdepth(self):
      def path(name):
          return os.path.join(
              current_file_dir, "images", "bitdepths", name
          )
  
      # Test images with varying bitdepth and check correctness against 4 reference pixels
      images_info = [
          # path, bitdepth, pixel_data[0, 0], pixel_data[0, 1], pixel_data[0, 200], pixel_data[40, 400]
          (
              path("color_1bit.png"),
              [0, 0, 0],
              [0, 0, 0],
              [0, 255, 255],
              [255, 255, 0],
          ),
          (
              path("color_2bit.png"),
              [0, 0, 0],
              [0, 0, 0],
              [85, 255, 170],
              [170, 170, 85],
          ),
          (
              path("color_4bit.png"),
              [0, 0, 0],
              [0, 0, 0],
              [68, 221, 187],
              [153, 187, 102],
          ),
          (
              path("color_8bit.png"),
              [0, 0, 0],
              [0, 1, 2],
              [73, 219, 182],
              [146, 182, 109],
          ),
          (
              path("color_16bit.png"),
              [0, 0, 0],
              [0, 1, 2],
              [73, 219, 182],
              [146, 182, 109],
          ),
          (path("gray_1bit.png"), 0, 0, 0, 255),
          (path("gray_2bit.png"), 0, 0, 85, 170),
          (path("gray_4bit.png"), 0, 0, 68, 153),
          (path("gray_8bit.png"), 0, 0, 73, 146),
          (path("gray_16bit.png"), 0, 0, 73, 146),
          (
              path("palette_1bit.png"),
              [127, 0, 255],
              [127, 0, 255],
              [127, 0, 255],
              [255, 0, 0],
          ),
          (
              path("palette_2bit.png"),
              [127, 0, 255],
              [127, 0, 255],
              [42, 220, 220],
              [212, 220, 127],
          ),
          (
              path("palette_4bit.png"),
              [127, 0, 255],
              [127, 0, 255],
              [8, 189, 232],
              [178, 242, 149],
          ),
          (
              path("palette_8bit.png"),
              [127, 0, 255],
              [127, 0, 255],
              [18, 199, 229],
              [164, 248, 158],
          ),
      ]
  
      for (
          path,
          color_0_0,
          color_0_1,
          color_0_200,
          color_40_400,
      ) in images_info:
          img = image.Image(path)
          data = img.pixel_data
          ref_type = type(color_0_0)
          self.assertEqual(ref_type(data[0, 0]), color_0_0)
          self.assertEqual(ref_type(data[0, 1]), color_0_1)
          self.assertEqual(ref_type(data[0, 200]), color_0_200)
          self.assertEqual(ref_type(data[40, 400]), color_40_400)
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import array
  import unittest
  from PIL import Image
  import os
  from ..data_structures import image
  from ..None import SArray
  from ..toolkits.image_analysis import image_analysis
  from ..toolkits._main import ToolkitError
  from .._deps import numpy, HAS_NUMPY
label_desc: Use image node_id 13 for calling the ImageClassTest obj's underlying member method code with example usage: obj.test_png_bitdepth() and returns: os