Develop Reference

Why am I getting "cv2.error: Unknown C++ exception from OpenCV code" when I'm using cv2.BackgroundSubtractorKNN() in Python?

A simple program to show the feed from my webcam is running fine. I'm getting the error only when I try to run cv2.BackgroundSubtractorKNN() within the loop.
I have applied the following fix:
Uninstalled the latest version of OpenCV (which I was using) and installed an older version 4.5.4. But the error still persists.
Here's my code and the corresponding messages in the terminal.
import cv2
cap = cv2.VideoCapture(0)
mog = cv2.BackgroundSubtractorKNN()
while(True):
ret, frame = cap.read()
fgmask = mog.apply(frame)
cv2.imshow('frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
Message in terminal
PS D:\Python ground up\Open_CV> python -u "d:\Python ground up\Open_CV\backgroundsub.py"
Traceback (most recent call last):
File "d:\Python ground up\Open_CV\backgroundsub.py", line 7, in <module>
fgmask = mog.apply(frame)
cv2.error: Unknown C++ exception from OpenCV code

I think it's createBackgroundSubtractorKNN not BackgroundSubtractorKNN

Get Live Stream from a Camera connected via usb using python

I want to grab live images from a camera which is connected via USB with my computer.
I am using an Industrial Camera with usb port.
At device manager the camera is shown with its name and id so I think it is connected to PC.
I ran a 'findcam' program but it is not showing any existance of camera
import cv2
cap = cv2.VideoCapture(0)
while True:
ret, frame = cap.read()
cv2.imshow('Live Video', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
The given code which i tried is running for webcam on my laptop but when the same code i run on my PC with an external camera.
it constantly showing an error.
The Error:
Traceback (most recent call last):
File "C:/Users/Admin/PycharmProjects/industrialcamera/ICvideocapture.py", line 11, in <module>
cv2.imshow('Live Video', frame)
cv2.error: OpenCV(4.1.0) C:\projects\opencv-python\opencv\modules\highgui\src\window.cpp:352: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'cv::imshow'
I tried changing Index -1 , 0 , 1 but the error is constant
please help to find, weather it is my PC problem or camera problem or is their is any other way to stream(in python)
Thank You

I started your code on my PC and it works fine. Try to set the camera resolution manually, if you have an error with size.width and size.height, something like this:
cap = cv2.VideoCapture(0)
cap.set(3,1280)
cap.set(4,920)

You may have installed the wrong version of OpenCV which doesn't support video. Uninstall everything of opencv and then run:
pip install opencv-python
(Source: cv2.VideoCapture.open() always returns FALSE)

Try to install opencv-contrib-python via pip: pip install opencv-contrib-python or maybe try to upgrade the version of it : pip install opencv-python --upgrade

you can debugg by checking the ret value :
import cv2
cap = cv2.VideoCapture(0)
counter = 0
while True:.
ret, frame = cap.read()
if ret :
cv2.imshow('Live Video', frame)
print(f" frame {counter} : ok ")
if not ret :
print(f" frame {counter} : ...")
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()

Python OpenCV Camera Error

For some reason, I cannot read camera video data using OpenCV and Python 3.
Here is the code I am using:
import cv2
import numpy as np
cap = cv2.VideoCapture(0)
while(1):
_, frame = cap.read()
cv2.imshow('frame',frame)
k = cv2.waitKey(5) & 0xFF
if k == 27:
break
cap.release()
cv2.destroyAllWindows()
This code returns the following error:
Traceback (most recent call last):
File "C:\Path\To\File\VideoTest.py", line 10, in <module>
cv2.imshow('frame',frame)
cv2.error: D:\Build\OpenCV\opencv-3.3.1\modules\highgui\src\window.cpp:339: error: (-215) size.width>0 && size.height>0 in function cv::imshow
The computer is running Windows Server 2012 R2 and has one USB webcam permanently in use in addition to the new one I am trying to read data from. I have tried changing the line cap = cv2.VideoCapture(0) to cap = cv2.VideoCapture(1) and had an identical error.
I tried replicating the error on my laptop using the same code and USB webcam, but it worked perfectly and I was able to stream the video.
**EDIT**
To debug, I ran the following program line-by-line in the Python shell.
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
print(cap.read())
cap = cv2.VideoCapture(1)
print(cap.read())
The code outputted (False, None) twice.

OpenCV Python Assertion failed error when playing .avi

I am just beginning to learn OpenCV and am working through the tutorials here: https://opencv24-python-tutorials.readthedocs.io/en/stable/py_tutorials/py_gui/py_video_display/py_video_display.html
This is the code I've written to play the sample video.
import numpy as np
import cv2
cap = cv2.VideoCapture('samples/vtest.avi')
while (cap.isOpened()):
ret, frame = cap.read()
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.imshow('frame', gray)
if cv2.waitkey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
This is the error message I get:
OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, file /tmp/opencv-20161020-7399-1yrk4nm/opencv-2.4.13.1/modules/imgproc/src/color.cpp, line 3739
Traceback (most recent call last):
File "vidFile_tutorial.py", line 14, in <module>
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.error: /tmp/opencv-20161020-7399-1yrk4nm/opencv-2.4.13.1/modules/imgproc/src/color.cpp:3739: error: (-215) scn == 3 || scn == 4 in function cvtColor
I'm unsure that the problem is an assertion fail error since I've chosen the file as specified by the tutorial. Moreover, when I attempt to play vtest.avi manually I encounter a codec error with QuickTime. Therefore, I suspect it's video codec issues with OpenCV. But I'm unsure if the diagnosis is correct and how I would go about fixing it.
Thanks in advance.

Okay,
So I've managed to resolve the issue by using OpenCV 3.1.0 rather than 2.4.13.1.
With OpenCV 3.1.0 everything works fine.

Trouble with raspberry pi and OpenCV

I have a project in raspberry pi and I am using python. However I have a problem with the OpenCV when I am trying to run this code:
`import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Our operations on the frame come here
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
# Display the resulting frame
cv2.imshow('frame',gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()`
I get this error:
OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, file /home/pi/opencv-3.1.0/modules/imgproc/src/color.cpp, line 8000
Traceback (most recent call last):
File "test.py", line 11, in <module>
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.error: /home/pi/opencv-3.1.0/modules/imgproc/src/color.cpp:8000: error: (-215) scn == 3 || scn == 4 in function cvtColor"
I have Python 3.4.2,OpenCV 3.1.0 and Numpy 1.8.2.

So I found an answer. All I had to do was run this code on my raspberry pi:
sudo modprobe bcm2835-v4l2
Thank you for all the help.