Qt and opencv app not working in virtual environment

Question

I created a GUI app using pyqt5 and opencv. The app works fine without activating the virtual env but when I activate the virtual env and run the app it shows this error:

QObject::moveToThread: Current thread (0x125b2f0) is not the object's thread (0x189e780).
Cannot move to target thread (0x125b2f0)

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/home/deepak/Desktop/SampleApp/lib/python3.9/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

I tried running an example pyqt5 code (without importing opencv) and another code (only using opencv) both worked fine in the virtual env.

Operating System: Parrot OS 4.11

Python Version: 3.9.2

Asked By: deepakgupta191199

||

Source

Answer 1

The problem is that the version of Qt with which opencv was compiled is not similar to the one used by PyQt5 causing a conflict.

A possible solution is to indicate to use the Qt plugins used by PyQt5.

import os
from pathlib import Path

import PyQt5
from PyQt5.QtWidgets import QWidget # others imports
import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = os.fspath(
    Path(PyQt5.__file__).resolve().parent / "Qt5" / "plugins"
)
# ...

For PySide2:

import os
from pathlib import Path

import PySide2
from PySide2.QtWidgets import QWidget # others imports
import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = os.fspath(
    Path(PySide2.__file__).resolve().parent / "Qt" / "plugins"
)
# ...

Update:

A better option is to use QLibraryInfo to get the plugins folder path:

import os

from PyQt5.QtCore import QLibraryInfo
# from PySide2.QtCore import QLibraryInfo

import cv2

os.environ["QT_QPA_PLATFORM_PLUGIN_PATH"] = QLibraryInfo.location(
    QLibraryInfo.PluginsPath
)

Answered By: eyllanesc

Answer 2

I solved the issue by downgrading the cv2 version, simply run

python3 -m pip install opencv-contrib-python==4.1.0.25

I used to have the 4.5.3.56

Answered By: Baladi Mohammed Omar

Answer 3

A simple solution would be to remove all the openCV you have in your environment

pip uninstall opencv-python opencv-python-headless opencv-contrib-python

then just install

pip install opencv-python-headless

Answered By: A.M

Answer 4

I found a way to solve this problem, by pip install opencv-python-headless instead of opencv-python. but with opencv-python-headless, it cause opencv problem when use cv2.imshow or cv2.namedWindow to try to open a image window.

I got this error

Traceback (most recent call last):
File "", line 1, in
cv2.error: OpenCV(4.5.4) /tmp/pip-req-build-4x5kub8r/opencv/modules/highgui/src/window.cpp:1257: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Cocoa support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function ‘cvNamedWindow’

Answered By: Vishesh Saxena

Qt and opencv app not working in virtual environment

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