遇到 AxisError：轴 1 超出维度 0 数组的范围

Question

I was just trying to make a body recognization feature but I am encountering with this axis error.

import cv2
import time
import numpy as np

## Preparation for writing the ouput video
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc,20.0, (640,480))

##reading from the webcam 
cap = cv2.VideoCapture(0)

## Allow the system to sleep for 3 seconds before the webcam starts
time.sleep(3)
count = 0
background = 0

## Capture the background in range of 60
for i in range(60):
    ret,background = cap.read()
background = np.flip(background,axis=1)

AxisError                                 
Traceback (most recent call last) <ipython-input-6-28a19252eb8f> in <module>()
      for i in range(60):
           ret,background = cap.read()
 ---> background = np.flip(background,axis=1) AxisError: axis 1 is out of bounds for array of dimension 0

Answer 1

If you're getting dimension zero, it probably means the capture failed so you've got a zero-sized array. Test against ret to make sure it's set to True :

# ...
ret,background = cap.read()

if not ret:
    raise RuntimeError("Couldn't capture an image")

background = np.flip(background,axis=1)

You could also check the capture is actually open before trying to grab a frame:

# ...

if not cap.isOpened():
     raise RuntimeError("Capture is not open - is the webcam connected?")

# ... Read the frame, check ret, flip it, etc.

A side-note: I'm not sure if this is on purpose, but you're also performing the flip only on the last frame as it's outside of the for-loop. If you intend to do it for every frame, it should be indented. You're throwing away the first 59 background frames you capture.