Python OpenCV imshow fails

Question

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?

what does "print img" show?

user1261273
– user1261273

2018-02-01 11:02:59 +00:00
Commented Feb 1, 2018 at 11:02 — user1261273
– user1261273, Commented Feb 1, 2018 at 11:02
Unrelated : why 2.7? why not 3.6.x ?

Patrick Artner
– Patrick Artner

2018-02-01 11:03:11 +00:00
Commented Feb 1, 2018 at 11:03 — Patrick Artner
– Patrick Artner, Commented Feb 1, 2018 at 11:03
Try from matplotlib import pyplot as plt.

Thomas Kühn
– Thomas Kühn

2018-02-01 11:03:17 +00:00
Commented Feb 1, 2018 at 11:03 — Thomas Kühn
– Thomas Kühn, Commented Feb 1, 2018 at 11:03
@jms print img shows the rgb values

Peter111
– Peter111

2018-02-01 11:06:47 +00:00
Commented Feb 1, 2018 at 11:06 — Peter111
– Peter111, Commented Feb 1, 2018 at 11:06
@Thomas Kühn this doesnt appear to change anything

Peter111
– Peter111

2018-02-01 11:07:10 +00:00
Commented Feb 1, 2018 at 11:07 — Peter111
– Peter111, Commented Feb 1, 2018 at 11:07

MAhipal Singh · Accepted Answer · 2018-02-14 14:28:06Z

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)

edited Feb 14, 2018 at 14:28

MAhipal Singh

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answered Feb 14, 2018 at 13:48

Nicolas Fuchs

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Comments

Peter111 · Accepted Answer · 2018-03-01 22:14:49Z

1

Apparently

pip install python-opencv

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

answered Mar 1, 2018 at 22:14

Peter111

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Comments

Rogelio Triviño · Accepted Answer · 2019-06-21 16:52:42Z

0

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

answered Jun 21, 2019 at 16:52

Rogelio Triviño

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