参考：

https://github.com/llSourcell/Object_Detection_demo_LIVE/issues/6

https://*.com/questions/52739143/opencv-error-215assertion-failed-vscncontainsscn-vdcncontainsdcn

错误发生于opencv颜色空间转换时：

 im_lab = cv2.cvtColor(im_bgr, cv2.COLOR_BGR2LAB)

根据上面第二个链接里的回答，数据不能是浮点型，只能是整型。但根据我的实验，float64会报如题的错误，但只要改成float32就可以运行。

im_bgr = im_bgr.astype(np.float64) # throws an error in the title

im_bgr = im_bgr.astype(np.float32) # runs without error