old_contents: import os.path as op
  import numpy as np
  import nibabel as nib
  import matplotlib.pyplot as plt
  import seaborn as sns
  
  def plot_mask_distribution(fname, ax=None, hist=False):
      """Plot the distribution of voxel coordinates in a mask file.
  
      Parameters
      ----------
      fname : string
          path to binary mask file
  
      Returns
      -------
      ax : matplotlib axis object
          axis with plot on it
  
      """
      if ax is None:
          ax = plt.subplot(111)
      img = nib.load(fname)
      mask = img.get_data()
      aff = img.get_affine()
      vox = np.where(mask)
      vox = np.vstack([vox, np.ones(mask.sum())])
      coords = np.dot(aff, vox)[:-1]
      colors = sns.get_color_list()[:3]
      for axis, data, color in zip(["x", "y", "z"], coords, colors):
          if hist:
              sns.kdeplot(data, hist=True, label=axis, color=color, ax=ax)
          else:
              sns.kdeplot(data, shade=True, label=axis, color=color, ax=ax)
      ax.legend()
      ax.set_title(op.basename(fname))
      return ax
  
new_contents: import numpy as np
  import nibabel as nib
  import matplotlib.pyplot as plt
  import seaborn as sns
  
  def plot_mask_distribution(mask_img, hist=False):
      """Plot the distribution of voxel coordinates in a mask image or file.
  
      Parameters
      ----------
      fname : string or nibabel image
          path to binary mask file or image object with data and affine
  
      Returns
      -------
      ax : matplotlib axis object
          axis with plot on it
  
      """
      if ax is None:
          ax = plt.subplot(111)
      if isinstance(mask_img, basestring):
          img = nib.load(mask_img)
      else:
          img = mask_img
      mask = img.get_data()
      aff = img.get_affine()
      vox = np.where(mask)
      vox = np.vstack([vox, np.ones(mask.sum())])
      coords = np.dot(aff, vox)[:-1]
      colors = sns.get_color_list()[:3]
      for axis, data, color in zip(["x", "y", "z"], coords, colors):
          if hist:
              sns.kdeplot(data, hist=True, label=axis, color=color, ax=ax)
          else:
              sns.kdeplot(data, shade=True, label=axis, color=color, ax=ax)
      ax.legend()
      return ax
  
subject: Allow plot_mask to take nibabel image