class_docstr: Convert color space from RGB to LAB.
class_docstr_tok: ["Convert","color","space","from","RGB","to","LAB","."]
docstr: Convert color space from RGB to LAB.
  
  Args:
     img(np.ndarray): Original RGB image.
  
  Return:
      img(np.ndarray): Converted LAB image.
code: def rgb2lab(self, rgb: np.ndarray) -> np.ndarray:
      """
      Convert color space from RGB to LAB.
  
      Args:
         img(np.ndarray): Original RGB image.
  
      Return:
          img(np.ndarray): Converted LAB image.
      """
      lab = self.xyz2lab(self.rgb2xyz(rgb))
      l_rs = (lab[[0], :, :] - 50) / 100
      ab_rs = lab[1:, :, :] / 110
      out = np.concatenate((l_rs, ab_rs), axis=0)
      return out
  
imports: import random
  from typing import Callable, Union, List, Tuple
  import cv2
  import PIL
  import numpy
  import paddlehub.vision.functional
label_desc: Use image node_id 3 for calling the RGB2LAB obj's underlying member method code with example usage: obj.rgb2lab(rgb) and returns: out