code: def cell():
      """Cell floating in saline.
  
      This is a quantitative phase image retrieved from a digital hologram using
      the Python library ``qpformat``. The image shows a cell with high phase
      value, above the background phase.
  
      Because of a banding pattern artifact in the background, this image is a
      good test of thresholding algorithms. The pixel spacing is 0.107 µm.
  
      These data were part of a comparison between several refractive index
      retrieval techniques for spherical objects as part of [1]_.
  
      This image is CC0, dedicated to the public domain. You may copy, modify, or
      distribute it without asking permission.
  
      Returns
      -------
      cell : (660, 550) uint8 array
          Image of a cell.
  
      References
      ----------
      .. [1] Paul Müller, Mirjam Schürmann, Salvatore Girardo, Gheorghe Cojoc,
             and Jochen Guck. "Accurate evaluation of size and refractive index
             for spherical objects in quantitative phase imaging." Optics Express
             26(8): 10729-10743 (2018). :DOI:`10.1364/OE.26.010729`
      """
      return _load("data/cell.png")
  
imports: import numpy
  import shutil
  from ..util.dtype import img_as_bool
  from ._registry import registry, registry_urls
  from ..None import __version__
  import os.path
  import os
label_desc: Use image node_id 19 for calling a global function with example usage: cell() and returns: _load