code: def _universal_thresh(img, sigma):
      """Universal threshold used by the VisuShrink method"""
      return sigma * np.sqrt(2 * np.log(img.size))
  
imports: import functools
  from math import ceil
  import numbers
  import scipy.stats
  import numpy
  from ..util.dtype import img_as_float
  from .._shared import utils
  from .._shared.utils import _supported_float_type, warn
  from ._denoise_cy import _denoise_bilateral, _denoise_tv_bregman
  from ..None import color
  from ..color.colorconv import ycbcr_from_rgb
label_desc: Use image node_id 9 for calling a global function with example usage: _universal_thresh(img, sigma) and returns: unknown