如何将采集到的人脸信息的坐标位置调用出来？我跟着人脸识别的教学视频操作，发现并不能正常运行。

[bzvo]

while(True):
    clock.tick() # Track elapsed milliseconds between snapshots().
    img = sensor.snapshot() # Take a picture and return the image.

    objects = img.find_features(face_cascade, threshold=0.75, scale=1.35)
    if objects:
        max_blob = find_max(objects)
        pan_error = max_blob.cx()-img.width()/2
        tilt_error = max_blob.cy()-img.height()/2

        print("pan_error: ", pan_error)

        img.draw_rectangle(max_blob.rect()) # rect

        pan_output=pan_pid.get_pid(pan_error,1)/2
        tilt_output=tilt_pid.get_pid(tilt_error,1)
        print("pan_output",pan_output)
        pan_servo.angle(pan_servo.angle()+pan_output)
        tilt_servo.angle(tilt_servo.angle()-tilt_output)
![0_1561518235957_}`8~7DP7X6_]2FW`IA%J3{M.png](https://fcdn.singtown.com/4654577d-b6fc-4356-8548-328ea224ffa7.png)