I got same problem, it was from opencv-python version problem for me.
My Linux machine’s environment is as following:

$ cat /etc/lsb-release 
...
DISTRIB_DESCRIPTION="Ubuntu 18.04.5 LTS"
$ date
Tue Aug 11 11:43:16 KST 2020
$ python --version
Python 3.7.8
$ pip list|grep Qt
PyQt5                5.15.0
PyQt5-sip            12.8.0
$ pip list|grep opencv-python
opencv-python        4.3.0.38

I downgraded opencv-python 4.3.0.38 to 4.3.0.36.

$ pip uninstall opencv-python
$ pip install opencv-python==4.3.0.36
$ pip list|grep opencv-python
opencv-python        4.3.0.36

First of all, uninstall any versions of OpenCV you may have installed. If you installed using pip:

sudo pip uninstall opencv-python

Next, try installing OpenCV using your Linux distro’s package manager. For Ubuntu/Debian, this is:

sudo apt install libopencv-dev python3-opencv

This can happen if you are using an Anaconda virtual environment and did both conda install pyqt⁽¹⁾ and pip install opencv-python. This creates a conflict between the two PyQt versions (opencv-python ships with its own) and causes the errors.

The solution is to install PyQt via pip, i.e. pip install PyQt5.

_{(1) Or anything that depends on pyqt, e.g. conda install matplotlib.}

I was able to fix this problem by installing new pyqt.

if you are using anaconda, just write down below:

$ conda install pyqt

This problem is due to the conflict between opencv-python’s own Qt5 and the one used by other packages. In my case, matplotlib is installed via conda, then pyqt is also installed as a matplotlib‘s dependency. My solution is as follows:

1. Uninstall matplotlib: conda remove matplotlib
2. Install opencv-python and matplotlib: pip install matplotlib opencv-python

Now, matplotlib installed via pip doesn’t require pyqt and the conflict is solved.

Note: The latest version 4.5.4.x gets error with python 3.9, consider using lower version such as 4.5.1.x in this case.

I solved this issue and I posted my solution in related issue on OpenCV github page. But for your convenience, I will post it here also.

In my case, I did almost all the solutions:

• installing using pip3 install opencv-python
• installing using apt install python-opencv
• I followed @areche solution, I end up with kdelibs5-plugins which was an important module for most of my desktop environments, so I give up on uninstalling it.

Finally, I found a solution for my case

• pip uninstall opencv-python on all instances of my python and virtual environments
• pip3 uninstall opencv-python on all instances of my python and virtual environments
• sudo apt remove python-opencv

then I downloaded the most recent opencv, in my case opencv-4.1.1 , I build it.
for building :

mkdir build; cd build; ccmake ..
then I pressed pressed c, again pressed c, then pressed g to generate make files, then
sudo make -j8
after successful building, I copied buildlibpython3cv2.cpython.xxxxxx.so to usr/local/lib/python3.5/dist-packages/ and renamed it to cv2.so
Do the same for each virtualenv that you have. ( I’m not sure if it is logical, but it worked for me).

then everything worked fine without any error.

refer to: https://blog.csdn.net/flyfor2013/article/details/110132458

pip3 uninstall opencv-python

pip3 install opencv-python==4.1.1.26

when I downgrade opencv-python 4.5 -> 4.1.1.26 then Ok

pip3 >= 20.3 use: pip3 install --use-deprecated=legacy-resolver opencv-python==

pip3 >= 9.0 use: pip3 install opencv-python==

and I try

pip3 uninstall opencv-python

pip3 install opencv-python==4.3.0.36

Ok, too

Just reinstall opencv-python lib, it’s OK.

pip uninstall opencv-python
pip install opencv-python==4.2.0.34

The version 4.2 is the latest opencv python that don’t throw this error. I tried 4.3 or 4.4 +, it’s don’t work.

The main reason of this question may be the conflict between PyQt5 and OpenCV.

The openCv author says that this problem comes from different Qt versions in openCv and the linux distro. That is: openCv comes with Qt4, but Qt5 is already installed.

The issue is with OpenCV version, The following version solved all issues for me.

pip uninstall opencv-python
pip install opencv-python==4.1.2.30

I am using – Python 3.8.5 with conda

I tried with upgrading pyqt too but it didn’t work

I tried the above mentioned method and could get opencv module working for my project which uses python3.x interpreter.

After performing few experiments, i got it working by doing the below steps:

1) Install opencv-python in your machine using:

sudo pip3 install opencv-python

2) On the python3.x terminal find the version:

>>> import cv2
>>> cv2.__version__
'3.4.1'

3) Get the same version of OpenCV from their official page.

4) Perform the CMake settings as mentioned in opencv tutorial.
Note the location specified in PYTHON3_PACKAGES_PATH

5) Once build has been performed, got to the install location specified in PYTHON3_PACKAGES_PATH. Move the library named cv2.cpython-*-gnu.so to the current python3.x dist-packages path:

usr/local/lib/python3.5/dist-packages/cv2

6) Reload your python3 project and try again!

This problem not present if runing opencv without virtualenviroment.
My system:
Kbuntu 18.04 LTS
GTX 1050
CUDA 9.2
Tensorflow 1.9

I had the same problem when i tried to run a detectron2 demo. My OS is Centos7 and i
uninstall some applications about qt.

find applications about qt.

yum list installed |grep qt

remove applications

yum -y remove xxx...

This error occurs in higher versions of openCv like 4.3.0.38 or higher, i tried 4.3.0.36 version with pip and this problem solved for me, but in lower version i were facing lots of problems, like window not loading correctly,If are using Ubuntu i would recommend you to uninstall opencv from your system completely and try to reinstall with command given below,

pip install opencv-contrib-python3

It is the compatibility issue. Even the way of “conda install install pyqt” does work. Please make sure that you can install the opencv libraries with the specific versions. Higher versions may incur the same issues.

pip install opencv-python==4.1.1.26
pip install opencv-contrib-python==4.1.1.26

Cheers,

I had the same problem and I did not find any solution. By trial and error, I found that my OpenCV version is corrupted. As a result, I deleted it and install a new fresh one. You can use one of these two options:
1. Terminal
run brew uninstall opencv3 to uninstall opencv
then install it using sudo apt-get install libopencv-dev python-opencv command.

2. Anaconda
Actually, I used this method for my own problem.

1. open anaconda
2. go to the environment section and select your environment as follow:
   
   then click on installed and search for opencv:
   
   select opencv package and uninstall it. then try to re-install opencv by selecting not installed and searching for opencv. be careful to install the correct version.
   

In my application I wanted to use PyQt without any of opencv’s GUI functionality, so the solution was to remove my current vertion of opencv-python, then instead pip install opencv-python-headless (or opencv-contrib-python-headless if you prefer). That way, opencv would be installed without its conflicting Qt library.

See: https://github.com/opencv/opencv-python#installation-and-usage

Downgrade the python version from 3.9.13 to 3.8.10

conda install python=3.8.10

pip install opencv-python==4.5.2.54

worked for me.

My system environment: Ubuntu 20.04 Anaconda 3.8

I was used matplotlib to display images and face this problem.
pip install opencv-python-headless not work for me.

pip uninstall pyqt5 then pip install pyqt5==5.12 and it works well.

Was facing the same error but from a different module but the problem remains the same my opencv is not compatible with the module I am using after searching every where found this solution.

pip install opencv-python-headless

Might not work but you can easily revert the change but removing the pip

pip uninstall opencv-python-headless

I encountered the same issue, and I have resolved it. The reason was that I had installed opencv-python version 4.8 using pip while also installing opencv version 4.5 using conda.

pip install opencv-python
conda install opencv==4.5 -c conda-forge

This may have caused a conflict, but I resolved the issue by uninstalling opencv-python.

pip uninstall opencv-python

I also meet this problem. I install opencv and PyQt throungh pip and solve it.
So I advise that you can keep the way the same that opencv and PyQt are installed.

Using opencv with PyQt5 worked for me:

import os
os.environ['QT_QPA_PLATFORM_PLUGIN_PATH'] = '/path/to/qt/plugin'

To find the path/to/qt/plugin:

from PyQt5.QtCore import QCoreApplication
    
# Initialize a QApplication instance to get access to system resources
app = QCoreApplication([])
    
# Get the path to the Qt plugins directory
qt_plugin_path = QCoreApplication.libraryPaths()[0]
print("Path to Qt plugins:", qt_plugin_path)

I am using a Debian GNU/Linux 12 (bookworm) on a raspberry pi 4. For me, the only solution was to install the headless version of opencv

pip uninstall opencv-python   
pip install opencv-python-headless

QObject::moveToThread: Current thread (0x728d7e0) is not the object’s
thread (0x74e4b20). Cannot move to target thread (0x728d7e0)
qt.qpa.plugin: Could not load the Qt platform plugin “xcb” in
“/home/amarihal/.local/lib/python3.8/site-packages/cv2/qt/plugins”
even though it was found. This application failed to start because no
Qt platform plugin could be initialized. Reinstalling the application
may fix this problem. Available platform plugins are: xcb, eglfs,
linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland,
wayland-xcomposite-egl, wayland-xcomposite-glx, webgl. Aborted (core
dumped)

if you got this error downgrade the opencv version

pip3 uninstall opencv-python

pip3 install opencv-python==4.3.0.36

try the above one
worked for me

As stated previously this is caused due to a conflict between the version of Qt used in the opencv package with another existing package’s.
For me this was pyqt!
removing pyqt using conda remove pyqt solved the issue for good.

The answer of @Mateen works great if you have Ubuntu version 17 and above. For Ubuntu 16, it’s better to compile from sources your opencv python. As @Varun mentioned, follow the opencv tutorial. However, to successfully compile opencv with python 3 I have to add some flags in cmake command:


cmake -DCMAKE_BUILD_TYPE=RELEASE -DPYTHON_DEFAULT_EXECUTABLE=$(which python3) -DPYTHON_INCLUDE_DIR2=/usr/include/x86_64-linux-gnu/python3.5m/ -DPYTHON3_NUMPY_INCLUDE_DIRS=/usr/local/lib/python3.5/dist-packages/numpy/core/include/ ..


Hope that will be helpful.

I don’t know why, but installation of matplotlib solved for me the problem with the error

QObject::moveToThread: Current thread (0x1d2c9cf0) is not the object's thread (0x1d347b20).
Cannot move to target thread (0x1d2c9cf0)

I emphasize that I prepared fresh conda environment where matplotlib was installed. Opencv was installed by pip in conda env as follow pip install opencv-python opencv-contrib-python.

I followed the solution suggested by @Varun and it worked for me (using Python 3).
However, I didn’t install the built files, as I do not have the admin rights on the system where I need the cv package. A cmake, followed by make was enough, I then took the cv2.*.gnu file from ../build/lib/python3 folder and replaced the one in the site-packages/cv2 folder of my virtual environment

I had the same problem. Using opencv imshow function raised the moving thread error. Eventually, I found that Ubuntu 16.04 has a preinstalled pyqt5 while OpenCV needs pqty4.
Therefore, this may be caused by conflicting installations of Qt libraries. The following command fixed it for me:

sudo apt-get remove libqt5x11extras5 libqt5x11extras5-dev