code: def lch2lab(lch):
      """CIE-LCH to CIE-LAB color space conversion.
      LCH is the cylindrical representation of the LAB (Cartesian) colorspace
      Parameters
      ----------
      lch : array_like
          The N-D image in CIE-LCH format. The last (``N+1``-th) dimension must
          have at least 3 elements, corresponding to the ``L``, ``a``, and ``b``
          color channels.  Subsequent elements are copied.
      Returns
      -------
      out : ndarray
          The image in LAB format, with same shape as input `lch`.
      Raises
      ------
      ValueError
          If `lch` does not have at least 3 color channels (i.e. l, c, h).
      Examples
      --------
      >>> from skimage import data
      >>> from skimage.color import rgb2lab, lch2lab
      >>> img = data.astronaut()
      >>> img_lab = rgb2lab(img)
      >>> img_lch = lab2lch(img_lab)
      >>> img_lab2 = lch2lab(img_lch)
      """
      lch = _prepare_lab_array(lch)
  
      c, h = lch[..., 1], lch[..., 2]
      lch[..., 1], lch[..., 2] = c * np.cos(h), c * np.sin(h)
      return lch
  
imports: import numpy
  from scipy import linalg
  from warnings import warn
label_desc: Use image node_id 6 for calling a global function with example usage: lch2lab(lch) and returns: lch