code: def _save_cm(output_cmap, cmap, format="png", n_colors=256):
      """Save the colormap of an image as an image file."""
      # save the colormap
      data = np.arange(0.0, n_colors) / (n_colors - 1.0)
      data = data.reshape([1, n_colors])
      imsave(output_cmap, data, cmap=cmap, format=format)
  
imports: import copy
  import json
  import os
  import warnings
  from base64 import b64encode
  from io import BytesIO
  import matplotlib
  import numpy
  from matplotlib.image import imsave
  from nibabel.affines import apply_affine
  from nilearn.plotting.html_document import HTMLDocument
  from .._utils import fill_doc
  from .._utils.extmath import fast_abs_percentile
  from .._utils.niimg import safe_get_data
  from .._utils.niimg_conversions import check_niimg_3d
  from .._utils.param_validation import check_threshold
  from ..datasets import load_mni152_template
  from ..image import get_data, new_img_like, reorder_img, resample_to_img
  from ..plotting import cm
  from ..plotting.find_cuts import find_xyz_cut_coords
  from ..plotting.img_plotting import load_anat
  from .js_plotting_utils import colorscale, get_html_template
label_desc: Use image node_id 5 for calling a global function with example usage: _save_cm(output_cmap, cmap, format, n_colors) without return types