外部网络摄像头不适用于 Opencv 和 Python

Question

I'm using Python cv2 module to use to run a program.

I'm able to access the inbuilt webcam but when I using the external webcam, it doesn't work.

I have used all codes like

VideoCapture(1) # or any other no.s like 0,1,2,3 etc etc.

I have even disabled the inbuilt webcam using device manager.

but nothing works. I'm using pythonxy. I have tried in command prompt also. It still doesn't work.

I get the following error

runfile('C:/Users/Prashant/Documents/Python Scripts/Circledetection.py',     wdir=r'C:/Users/Prashant/Documents/Python Scripts')
OpenCV Error: Assertion failed (scn == 3 || scn == 4) in unknown function, file ..\..\..\modules\imgproc\src\color.cpp, line 3402
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 540, in runfile
    execfile(filename, namespace)
  File "C:/Users/Prashant/Documents/Python Scripts/Circledetection.py", line 27, in <module>
    prev_gray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
cv2.error: ..\..\..\modules\imgproc\src\color.cpp:3402: error: (-215) scn == 3 || scn == 4

Answer 1

You mentioned VideoCapture(0) to VideoCapture(1) .
"1" means external camera number.

import cv2
import numpy as np

cap = cv2.VideoCapture(1) 
while(1):
    ret, frame = cap.read()
    #print(height)
    #cv2.imshow("Cropped Image", crop_img)
    #gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

Answer 2

That assertion means that your image does not have 3 (RGB, BGR, etc) channels, or 4 channels (3 channels + alpha). This can be caused, obviously, by the image not existing at all.

While this might be because your camera isn't working, it's equally likely that your camera does not give usable frames for the first few read(), as it's still 'preparing' itself.

The easiest way to solve this, assuming you use something like retv, frame = cam.read() is to check if frame: or if retv: .

Have it skip over your processing if there's no image, and within a few frames you should have input that is readable.

Answer 3

Are you sure you are using the correct index? Using Videocapture you can also try to use Videocapture(-1) , since the external cam sometimes appears as the last element in the list of input. Videocapture also can return device names, so you could try to loop over the input devices index list and print their " friendly names", to make sure you are using the correct one.

Answer 4

OpenCV requires the following dependencies to work with the USB cameras. Install the dependencies from the following commands:

• libav video input/output development libraries

  sudo apt-get install libavformat-dev libavutil-dev libswscale-dev

• Video4Linux camera development libraries

  sudo apt-get install libv4l-dev

• OpenGL development libraries (to allow creating graphical windows)

   sudo apt-get install libglew-dev

• GTK development libraries (to allow creating graphical windows)

   sudo apt-get install libgtk2.0-dev

Answer 5

Thanks it works for me.

OpenCV requires the following dependencies to work with the USB cameras. Install the dependencies from the following commands:

libav video input/output development libraries

sudo apt-get install libavformat-dev libavutil-dev libswscale-dev Video4Linux camera development libraries

sudo apt-get install libv4l-dev OpenGL development libraries (to allow creating graphical windows)

sudo apt-get install libglew-dev GTK development libraries (to allow creating graphical windows)

sudo apt-get install libgtk2.0-dev