How to fix the error “QObject::moveToThread:” in opencv in python?

Question

I am using opencv2 in python with the code

import cv2
cv2.namedWindow(\"output\", cv2.WINDOW_NORMAL)       
cv2.imshow(\"output\",im)
cv2.resizeWindow(\'outp         


        

Answer 1

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.

Answer 2

This may be caused by conflicting installations of Qt libraries. The following command fixed it for me:

sudo apt-get remove libqt5x11extras5 libqt5x11extras5-dev

Answer 3

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

Answer 4

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.

Answer 5

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!

Answer 6

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...