Hi I'm using this code in pycharm and I have this error.please help me

python

asked 2019-09-02 13:41:10 -0600

updated 2019-09-02 14:59:39 -0600

berak
32993 ●7 ●81 ●312

import numpy as np import cv2

cap=cv2.VideoCapture(0)
while(True):
    ret,frame=cap.read()
    gray = cv2.cvtColor(frame ,cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) :
        break
cap.release()
cv2.destroyAllWindows()

and the error is:

OpenCV Error: Assertion failed (scn == 3 || scn == 4) in cv::cvtColor, file C:\build\master_winpack-bindings-win64-vc14-static\opencv\modules\imgproc\src\color.cpp, line 9748
Traceback (most recent call last):
  File "D:/python/examples_with_pyCharm/untitled2/Lesson3_VIDEO.py", line 7, in <module>
    gray = cv2.cvtColor(frame ,cv2.COLOR_BGR2GRAY)
cv2.error: C:\build\master_winpack-bindings-win64-vc14-static\opencv\modules\imgproc\src\color.cpp:9748: error: (-215) scn == 3 || scn == 4 in function cv::cvtColor

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answered 2019-09-02 15:04:24 -0600

berak
32993 ●7 ●81 ●312

updated 2019-09-02 15:34:18 -0600

it's a typical python nooooooob error. you're blindly pasting other ppls code.

you have to add CHECKS,

if the capture could be opened at all: if not cap.isOpened(): ...
if it (still) could read an image: if not img is NONE: ...

VideoCapture will NEVER throw any exceptions on failure, so you HAVE to check manually

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Well not throwing any exception was Design by the Open CV Library. It has pros(no stupid exception handling) and cons(its possible to make this error and therefore it will happen).

And yes Java and Python are easy to learn - so some People get a bit "lazy". Btw. you supplied the solution.

holger ( 2019-09-02 17:22:25 -0600 )edit

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answered 2019-09-03 06:42:38 -0600

supra56

943 ●9 ●6

In line 7: You can't do this if/else block conditionif cv2.waitKey(1) :. It will shut down in 1 seconds. Correct way to do this.

import cv2 as cv

cap=cv.VideoCapture(0)
while(True):
    ret,frame=cap.read()
    gray = cv.cvtColor(frame ,cv.COLOR_BGR2GRAY)
    cv.imshow('frame',gray)
    key = cv.waitKey(1)
    if key == 27:
        break
cap.release()
cv.destroyAllWindows()

Btw, I'm using Raspberry pi 4 w/4gb, opencv 4.1.0, Thonny3.2, python 3.7.3.

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Btw, Do not use boolean while True: Practically way to do this while cap.isOpened():

supra56 ( 2019-09-03 06:48:25 -0600 )edit

Another way to do this:

if cv2.waitKey(1) & 0xFF == ord('q'):

supra56 ( 2019-09-03 08:30:17 -0600 )edit

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Hi I'm using this code in pycharm and I have this error.please help me

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