code: def besselFilter(
      data, cutoff, order=1, dt=None, btype="low", bidir=True
  ):
      """return data passed through bessel filter"""
      try:
          import scipy.signal
      except ImportError:
          raise Exception(
              "besselFilter() requires the package scipy.signal."
          )
  
      if dt is None:
          try:
              tvals = data.xvals("Time")
              dt = (tvals[-1] - tvals[0]) / (len(tvals) - 1)
          except:
              dt = 1.0
  
      b, a = scipy.signal.bessel(order, cutoff * dt, btype=btype)
  
      return applyFilter(data, b, a, bidir=bidir)
  
file_path: pyqtgraph/pyqtgraph/flowchart/library/functions.py
imports: import numpy
  from ...metaarray import MetaArray
label_desc: Use image node_id 3 for calling a global function with example usage: besselFilter(data, cutoff, order, dt, btype, bidir) and returns: applyFilter