code: def bgr2gray(img, keepdim=False):
      """Convert a BGR image to grayscale image.
  
      Args:
          img (ndarray): The input image.
          keepdim (bool): If False (by default), then return the grayscale image
              with 2 dims, otherwise 3 dims.
  
      Returns:
          ndarray: The converted grayscale image.
      """
      out_img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
      if keepdim:
          out_img = out_img[..., None]
      return out_img
  
file_path: lavis/lavis/common/annotator/uniformer/mmcv/image/colorspace.py
imports: import cv2
  import numpy
label_desc: Use image node_id 2 for calling a global function with example usage: bgr2gray(img, keepdim) and returns: out_img