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('output', 400,400)
cv2.waitKey(0)
cv2.destroyAllWindows()

I have the error as

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

I debug and found that it happened when I use cv2.waitKey(0). How should I fix it? Thanks

Update: I am using 3.3.0.0. If I use older version, I have error

OpenCV Error: Unspecified error (The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Carbon support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script) in cvDestroyAllWindows, file /io/opencv/modules/highgui/src/window.cpp, line 577
Traceback (most recent call last):
  File "tools/demo_handbone.py", line 220, in <module>
    demo(net, im_name)
  File "tools/demo_handbone.py", line 159, in demo
    cv2.destroyAllWindows()
cv2.error: /io/opencv/modules/highgui/src/window.cpp:577: error: (-2) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Carbon support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function cvDestroyAllWindows

My guess is something odd happened regarding either Qt or the most recent version of opencv2 might have a bug. Did you just upgrade a package recently? — Mateen Ulhaq, Sep 28 '17 at 02:02
Try installing an older version. Did you use pip to install? — Mateen Ulhaq, Sep 28 '17 at 02:08
Yes. I use pip. How can I install an older version of opencv in python? Thanks — John, Sep 28 '17 at 02:11
`pip install opencv-python==` will list the available versions. Then you do `pip install opencv-python==3.1.0.0`, for example. — Mateen Ulhaq, Sep 28 '17 at 02:13
Thanks. I am using version 3.3.0.0. I tried to use older version but I got the error as my update question — John, Sep 28 '17 at 02:20
1. Run `sudo pip uninstall opencv-python`. 2. Which distro of Linux are you running? If it's Ubuntu/Debian, `sudo apt-get install libopencv-dev python-opencv`. — Mateen Ulhaq, Sep 28 '17 at 02:33
It worked now. Thanks so much. I will delete the question. Is it ok? — John, Sep 28 '17 at 02:36
Nice. I'll put it in answer format. (My friend was having the same error.) — Mateen Ulhaq, Sep 28 '17 at 02:37
If you have KDE installed, there is a conflict between system Qt and the wheel-bundled version. `sudo apt remove libqt5x11extras5` fixed the problem for me _BUT_ will basically kill KDE, so beware if you use that as your main gui. See: https://github.com/skvark/opencv-python/issues/46 — Akh, Sep 18 '18 at 19:47

score 30 · Answer 1 · edited Nov 07 '20 at 02:48

30

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

edited Nov 07 '20 at 02:48

Bora

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answered Aug 11 '20 at 02:52

Hill

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This is the only answer in this thread that worked for me! Thanks! – qalis Aug 29 '20 at 10:40
This lead to the following error for me: https://askubuntu.com/questions/342202/failed-to-load-module-canberra-gtk-module-but-already-installed – Martin Hahner Sep 16 '20 at 14:07
Downgrading worked also for me. Did a more strong downgrade from `4.5.3.56` to `4.1.2.30` – iGian Aug 11 '21 at 11:06

score 19 · Accepted Answer · edited Mar 29 '23 at 11:39

19

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

edited Mar 29 '23 at 11:39

larsaars

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answered Sep 28 '17 at 02:38

Mateen Ulhaq

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I am using `virtualenv` and my problem persists after 1. `$ pip uninstall opencv-python`. 2. `$ sudo apt-get install libopencv-dev python-opencv` 3. `$ pip install opencv-python` – Tushar Goswami Oct 03 '17 at 09:30
2

`opencv-python` in pip ships with a opencv 3 library, but `python-opencv` binding in `apt` uses the `libopencv-dev` library which is opencv2. So I believe your method doesn't solve the problem for those (and me) who need to use opencv3 in python. – jasper jia Oct 17 '17 at 08:29
1

Doesn't work (same error persists). opencv-python-3.3.0.10 in python vs. libopencv2.4 in OS – Dzmitry Lazerka Nov 25 '17 at 01:20
@TusharGoswami Facing the same, any update on the problem? – Saurav-- Mar 07 '18 at 06:26
11

This "solution" basically disables the use of virtual environments. – problemofficer - n.f. Monica Jan 26 '20 at 18:38
doesn't work for me https://pastebin.com/raw/BvsuyT6Z libopencv-highgui2.4v5 : Depends: libpng12-0 (>= 1.2.13-4) but it is not going to be installed – Mona Jalal Jan 26 '21 at 17:24
this solution is outdated for Ubuntu 20.04 – Mona Jalal Jan 26 '21 at 17:52
Thank you this solved my "Aborted (core dumped)" error that happens opening labelme – Yunus Emrah Uluçay Jun 21 '21 at 14:11
1

This worked for me: `sudo apt-get install python3-opencv` I do think it disables virtual environments though – Rashi Abramson Mar 20 '22 at 22:27

score 12 · Answer 3 · answered Dec 30 '20 at 17:30

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.}

score 9 · Answer 4 · answered Jun 11 '19 at 13:27

9

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

if you are using anaconda, just write down below:

$ conda install pyqt

answered Jun 11 '19 at 13:27

Jungwon Choi

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This worked for me while using python 3.7. This should be marked as the correct answer. – amit kumar Jul 04 '19 at 09:17
1

What would be the analogous package for pip? There is package with the name *pyqt* in pip. – problemofficer - n.f. Monica Jan 26 '20 at 18:52
This also worked for me :) Thank you :) – user123456098 Nov 21 '21 at 07:52

score 4 · Answer 5 · answered Aug 06 '19 at 12:33

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 build\lib\python3\cv2.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.

The problem seems to be related with KDE. After doing the [areche_solution](https://github.com/skvark/opencv-python/issues/46#issuecomment-495694090) everything worked just fine — ignacio, Apr 23 '20 at 12:01

score 4 · Answer 6 · edited Mar 21 '22 at 00:43

4

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

edited Mar 21 '22 at 00:43

Mateen Ulhaq

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answered Feb 19 '21 at 04:53

YU Chen Shih

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It seems to work for me, with version `opencv-python` version `4.2.0.34` or less (python version `3.8.5` and ubuntu `20.04`. – Come get some Mar 05 '21 at 15:37

score 4 · Answer 7 · edited May 08 '23 at 03:15

4

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.

edited May 08 '23 at 03:15

socasanta

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answered May 14 '21 at 05:11

Kun Zhan

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I have exaclty this version, "opencv-python==4.2.0.34", and I'm getting tons of this error :( – Tomasz Gandor Jun 25 '21 at 01:59

score 3 · Answer 8 · 2019-04-20T19:29:16.383

3

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.

edited Apr 20 '19 at 19:29

answered Apr 20 '19 at 19:23

score 3 · Answer 9 · answered Oct 25 '21 at 03:59

3

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:

Uninstall matplotlib: conda remove matplotlib
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.

answered Oct 25 '21 at 03:59

huyfam

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this helped me. Thanks a lot for sharing. I was using ubuntu 20. The conflict was caused by matplotlib and opencv-contrib-pyhon – Ali Waqas Jul 31 '22 at 22:22
This is the real problem. This solved the issue for me. Thanks – Arritmic Oct 03 '22 at 06:14

score 2 · Answer 10 · answered May 01 '21 at 17:45

2

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

answered May 01 '21 at 17:45

Vinay Verma

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score 1 · Answer 11 · answered May 24 '18 at 10:07

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!

score 0 · Answer 12 · answered Sep 10 '18 at 08:12

0

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

answered Sep 10 '18 at 08:12

Przemek

1

score 0 · Answer 13 · answered Jun 18 '20 at 02:10

0

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...

answered Jun 18 '20 at 02:10

ligansss

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Sudhanshu · Answer 14 · 2020-12-28T17:23:23.447

0

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

edited Dec 28 '20 at 17:23

answered Dec 28 '20 at 13:00

Sudhanshu

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pip install opencv-contrib-python3 ERROR: Could not find a version that satisfies the requirement opencv-contrib-python3 ERROR: No matching distribution found for opencv-contrib-python3 – Mona Jalal Jan 26 '21 at 17:43

score 0 · Answer 15 · answered Apr 26 '21 at 19:33

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,

score 0 · Answer 16 · answered Oct 23 '21 at 04:06

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.

open anaconda
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.

score 0 · Answer 17 · answered Sep 25 '22 at 18:38

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

score 0 · Answer 18 · answered Nov 08 '22 at 11:48

0

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.

answered Nov 08 '22 at 11:48

Happy Sonkar

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Alicas · Answer 19 · 2023-02-20T02:22:14.923

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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.

edited Feb 20 '23 at 02:22

answered Feb 20 '23 at 02:19

Alicas

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Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – xlmaster Feb 23 '23 at 19:43

score 0 · Answer 20 · answered May 09 '23 at 17:17

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

score 0 · Answer 21 · answered Aug 29 '23 at 10:02

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

score -1 · Answer 22 · answered Sep 28 '18 at 07:19

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.

score -1 · Answer 23 · answered Jan 08 '19 at 14:24

-1

I fixed this under Ubuntu 18.04 LTS by uninstalling any OpenCV packages from pip and apt and installing OpenCV directly from source. Maybe this tutorial will help:

https://www.pyimagesearch.com/2018/08/15/how-to-install-opencv-4-on-ubuntu/

answered Jan 08 '19 at 14:24

Matthias

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score -1 · Answer 24 · answered Mar 05 '19 at 22:06

-1

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.

answered Mar 05 '19 at 22:06

intheblack

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You should install either `opencv-python` or `opencv-contrib-python`, not both, as per the official documentation of the second package. – amit kumar Jul 04 '19 at 09:15

score -1 · Answer 25 · answered Jun 08 '19 at 23:52

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

score -1 · Answer 26 · answered Feb 03 '20 at 05:22

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

score -1 · Answer 27 · answered Jul 30 '20 at 09:02

I know the thread is a bit old but posting for anyone else out there, I faced the same problem and it was because even after running

pip3 uninstall opencv-python

there was another version of open-cv in my system which I checked by

pip list

(I'm guessing that pip only removes the first version it finds) So I ran this command again

pip3 uninstall opencv-python

And now simply installing opencv by

pip install opencv-python

worked for me.

score -1 · Answer 28 · answered Jul 27 '22 at 11:57

-1

In case you are using matplotlib, see this answer: https://stackoverflow.com/a/49887744/13268880

TL;DR: matplotlib.use('Agg')

answered Jul 27 '22 at 11:57

Nick Halden

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While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - [From Review](/review/late-answers/32346921) – Giorgos Myrianthous Aug 01 '22 at 15:02

score -2 · Answer 29 · answered Oct 10 '19 at 16:18

-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

answered Oct 10 '19 at 16:18

Mike Gashler

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This deletes important system libraries and can make your system unusable. Don't run this unless you know exactly what it does. – problemofficer - n.f. Monica Jan 26 '20 at 18:50

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

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