docs: def add_px_err(isoel, col1, col2, px_um, inplace=False):
          """Undo pixelation correction
  
          Isoelasticity lines are already corrected for pixelation
          effects as described in
  
          Mapping of Deformation to Apparent Young's Modulus
          in Real-Time Deformability Cytometry
          Christoph Herold, arXiv:1704.00572 [cond-mat.soft] (2017)
          https://arxiv.org/abs/1704.00572.
  
          If the isoealsticity lines are displayed with deformation data
          that are not corrected, then the lines must be "un"-corrected,
          i.e. the pixelation error must be added to the lines to match
          the experimental data.
  
          Parameters
          ----------
          isoel: list of 2d ndarrays of shape (N, 3)
              Each item in the list corresponds to one isoelasticity
              line. The first column is defined by `col1`, the second
              by `col2`, and the third column is the emodulus.
          col1, col2: str
              Define the fist to columns of each isoelasticity line.
              One of ["area_um", "circ", "deform"]
          px_um: float
              Pixel size [µm]
          """
          Isoelastics.check_col12(col1, col2)
          if "deform" in [col1, col2]:
              # add error for deformation
              sign = +1
          else:
              # subtract error for circularity
              sign = -1
          if col1 == "area_um":
              area_ax = 0
              deci_ax = 1
          else:
              area_ax = 1
              deci_ax = 0
  
          new_isoel = []
          for iso in isoel:
              iso = np.array(iso, copy=not inplace)
              ddeci = feat_emod.corrpix_deform_delta(area_um=iso[:, area_ax],
                                                     px_um=px_um)
              iso[:, deci_ax] += sign * ddeci
              new_isoel.append(iso)
          return new_isoel