code: def flow2rgb(flow, color_wheel=None, unknown_thr=1e6):
      """Convert flow map to RGB image.
  
      Args:
          flow (ndarray): Array of optical flow.
          color_wheel (ndarray or None): Color wheel used to map flow field to
              RGB colorspace. Default color wheel will be used if not specified.
          unknown_thr (str): Values above this threshold will be marked as
              unknown and thus ignored.
  
      Returns:
          ndarray: RGB image that can be visualized.
      """
      assert flow.ndim == 3 and flow.shape[-1] == 2
      if color_wheel is None:
          color_wheel = make_color_wheel()
      assert color_wheel.ndim == 2 and color_wheel.shape[1] == 3
      num_bins = color_wheel.shape[0]
  
      dx = flow[:, :, 0].copy()
      dy = flow[:, :, 1].copy()
  
      ignore_inds = (
          np.isnan(dx)
          | np.isnan(dy)
          | (np.abs(dx) > unknown_thr)
          | (np.abs(dy) > unknown_thr)
      )
      dx[ignore_inds] = 0
      dy[ignore_inds] = 0
  
      rad = np.sqrt(dx**2 + dy**2)
      if np.any(rad > np.finfo(float).eps):
          max_rad = np.max(rad)
          dx /= max_rad
          dy /= max_rad
  
      rad = np.sqrt(dx**2 + dy**2)
      angle = np.arctan2(-dy, -dx) / np.pi
  
      bin_real = (angle + 1) / 2 * (num_bins - 1)
      bin_left = np.floor(bin_real).astype(int)
      bin_right = (bin_left + 1) % num_bins
      w = (bin_real - bin_left.astype(np.float32))[..., None]
      flow_img = (1 - w) * color_wheel[bin_left, :] + w * color_wheel[
          bin_right, :
      ]
      small_ind = rad <= 1
      flow_img[small_ind] = 1 - rad[small_ind, None] * (
          1 - flow_img[small_ind]
      )
      flow_img[np.logical_not(small_ind)] *= 0.75
  
      flow_img[ignore_inds, :] = 0
  
      return flow_img
  
file_path: lavis/lavis/common/annotator/uniformer/mmcv/visualization/optflow.py
imports: from __future__ import division
  import numpy
  from annotator.uniformer.mmcv.image import rgb2bgr
  from annotator.uniformer.mmcv.video import flowread
  from .image import imshow
label_desc: Use image node_id 2 for calling a global function with example usage: flow2rgb(flow, color_wheel, unknown_thr) and returns: flow_img