錯誤發生於opencv顏色空間轉換時：
im_lab = cv2.cvtColor(im_bgr, cv2.COLOR_BGR2LAB)
根據上面第二個鏈接里的回答，數據不能是浮點型，只能是整型。但根據我的實驗，float64會報如題的錯誤，但只要改成float32就可以運行。
im_bgr = im_bgr.astype(np.float64) # throws an error in the title
im_bgr = im_bgr.astype(np.float32) # runs without error
參考：
https://github.com/llSourcell/Object_Detection_demo_LIVE/issues/6
https://stackoverflow.com/questions/52739143/opencv-error-215assertion-failed-vscncontainsscn-vdcncontainsdcn