title: cannot import name '_registerMatType' from 'cv2.cv2'
body: <p>I got below error message when I run <code>model_main_tf2.py</code> on Object Detection API:</p>
  <pre><code>Traceback (most recent call last):
    File &quot;/content/models/research/object_detection/model_main_tf2.py&quot;, line 32, in &lt;module&gt;
      from object_detection import model_lib_v2
    File &quot;/usr/local/lib/python3.7/dist-packages/object_detection/model_lib_v2.py&quot;, line 29, in &lt;module&gt;
      from object_detection import eval_util
    File &quot;/usr/local/lib/python3.7/dist-packages/object_detection/eval_util.py&quot;, line 36, in &lt;module&gt;
      from object_detection.metrics import lvis_evaluation
    File &quot;/usr/local/lib/python3.7/dist-packages/object_detection/metrics/lvis_evaluation.py&quot;, line 23, in &lt;module&gt;
      from lvis import results as lvis_results
    File &quot;/usr/local/lib/python3.7/dist-packages/lvis/__init__.py&quot;, line 5, in &lt;module&gt;
      from lvis.vis import LVISVis
    File &quot;/usr/local/lib/python3.7/dist-packages/lvis/vis.py&quot;, line 1, in &lt;module&gt;
      import cv2
    File &quot;/usr/local/lib/python3.7/dist-packages/cv2/__init__.py&quot;, line 9, in &lt;module&gt;
      from .cv2 import _registerMatType
  ImportError: cannot import name '_registerMatType' from 'cv2.cv2' (/usr/local/lib/python3.7/dist-packages/cv2/cv2.cpython-37m-x86_64-linux-gnu.so)
  </code></pre>
  <p>The weird thing is I run the same code before, it worked well but now it gives me an error.</p>