Python OpenCV imshow fails

问题

I installed opencv on my Ubuntu 14.04 system system with

pip install python-opencv

my Python version is 2.7.14

import cv2
cv2.__version__

tells me that I have the OpenCV version 3.4.0.

After that I wanted to follow the tutorial on the OpenCV website

import numpy as np
import cv2 as cv
img = cv.imread('messi5.jpg',0)
print img

It works fine until this point, but then I am supposed to enter

cv.imshow('image',img)

and I get the following error:

QObject::moveToThread: Current thread (0x233cdb0) is not the object's thread (0x2458430).
Cannot move to target thread (0x233cdb0)

QObject::moveToThread: Current thread (0x233cdb0) is not the object's thread (0x2458430).
Cannot move to target thread (0x233cdb0)

QPixmap: Must construct a QApplication before a QPaintDevice

Does anyone know what the problem is?

回答1:

Try checking if the image you are reading is loading

image = cv2.imread(filepath,0) #0 for gray scale
if image is None:
    print "Cant Load Image"  
else:
    cv2.imshow("Image", image)
    cv2.waitKey(0)

回答2:

Apparently

pip install python-opencv

is not working at all and should not be used. After I installed Opencv from their website it worked

回答3:

seems hard to install opencv on ubuntu, I finally get it with a docker image

https://hub.docker.com/r/jjanzic/docker-python3-opencv/

or you can download sources and make install as described on https://milq.github.io/install-opencv-ubuntu-debian/ using bash script

来源：https://stackoverflow.com/questions/48561126/python-opencv-imshow-fails