OpenCV 3.1.0 imshow in Linux does not work for webcam (Python)

I’m trying to use code from the official openCV tutorial for showing video from webcam using cv2.imshow() in Ubuntu/Python 3.6:

import numpy as np
import cv2
cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Our operations on the frame come here
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

And I get the following error for cv2.imshow():

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 cvShowImage

When searching for the error I stumbled upon this post as an alternate answer to similar questions:

If you installed OpenCV using the opencv-python pip package at any point in time, be aware of the following note, taken from https://pypi.python.org/pypi/opencv-python

IMPORTANT NOTE MacOS and Linux wheels have currently some limitations:

• video related functionality is not supported (not compiled with FFmpeg)
• for example cv2.imshow() will not work (not compiled with GTK+ 2.x or Carbon support)

Also note that to install from another source, first you must remove the opencv-python package

OpenCV error: the function is not implemented

OpenCV not working properly with python on Linux with anaconda. Getting error that cv2.imshow() is not implemented

Most other openCV functions work properly.

Is there an alternative to cv2.imshow() that uses standard anaconda libraries so I don’t have to recompile openCV or use Python 2.7?

Answer

I hacked together a quick and dirty snippet that uses matplotlib.animation and resembles what cv2.imshow() is expected to do with webcam video:

import cv2
import matplotlib.pyplot as plt
import matplotlib.animation as animation
cap = cv2.VideoCapture(0)
ret, frame = cap.read()
# The following is the replacement for cv2.imshow():
fig = plt.figure() 
ax = fig.add_subplot(111)
im = ax.imshow(cv2.cvtColor(frame, cv2.COLOR_BGR2RGB), animated=True)
def updatefig(*args):
    ret, frame = cap.read()
    im.set_array(cv2.cvtColor(frame, cv2.COLOR_BGR2RGB))
    return im
ani = animation.FuncAnimation(fig, updatefig, interval=10)
plt.show()

I found this very useful, as I was able to output many overlapping plots on top of the webcam video thanks to the fact that matplotlib.animation.FuncAnimation can animate as many plots as there are attached to the ax object as long as they are updated in the updatefig() function above.

Edit: As I was working in a Jupyter notebook, I added the following in order to see the video in a new window:

import matplotlib
matplotlib.use('qt5agg')