Assertion failed (scn == 3 || scn == 4)

[feakuru]

I am currently experiencing this on a Mi 13.3 laptop when trying to run a basic example like:

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()

Complete output:

OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cvtColor, file /io/opencv/modules/imgproc/src/color.cpp, line 10638
Traceback (most recent call last):
  File "main.py", line 11, in <module>
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.error: /io/opencv/modules/imgproc/src/color.cpp:10638: error: (-215) scn == 3 || scn == 4 in function cvtColor

I have checked this from two distributions: a Ubuntu 17.04 and a Kali from a Live USB.

[skvark]

Did you read the package description? It very clearly states:

IMPORTANT NOTE

MacOS and Linux packages do not support video related functionality (not compiled with FFmpeg).

Unfortunately you'll have to compile OpenCV manually until I get an FFmpeg enabled build working on Linux.

[feakuru]

@skvark sorry, totally missed that. Where do I get instructions to compile opencv manually?

[skvark]

This is a very good guide: http://www.pyimagesearch.com/2016/10/24/ubuntu-16-04-how-to-install-opencv/

[feakuru]

@skvark thank you!