imgHsv = cv2.cvtColor(img,cv2.COLOR_BGR2HSV) cv2.error: OpenCV(4.0.0)

Question

I have been trying to run a color detection on my webcam by using OpenCV, and it keeps getting the error as shown in the title, and below:

 imgHsv = cv2.cvtColor(img,cv2.COLOR_BGR2HSV)
cv2.error: OpenCV(4.0.0) C:\projects\opencv-python\opencv\modules\imgproc\src\color.cpp:181: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

The code that I wanted to run is:

import cv2
import numpy as np

frameWidth = 640
frameHeight = 480
cap = cv2.VideoCapture(1)
cap.set(3, frameWidth)
cap.set(4, frameHeight)

def empty(a):
    pass

cv2.namedWindow("HSV")
cv2.resizeWindow("HSV",640,240)
cv2.createTrackbar("HUE Min","HSV",0,179,empty)
cv2.createTrackbar("HUE Max","HSV",179,179,empty)
cv2.createTrackbar("SAT Min","HSV",0,255,empty)
cv2.createTrackbar("SAT Max","HSV",255,255,empty)
cv2.createTrackbar("VALUE Min","HSV",0,255,empty)
cv2.createTrackbar("VALUE Max","HSV",255,255,empty)

while True:

    _, img = cap.read(0)
    imgHsv = cv2.cvtColor(img,cv2.COLOR_BGR2HSV)

    h_min = cv2.getTrackbarPos("HUE Min","HSV")
    h_max = cv2.getTrackbarPos("HUE Max", "HSV")
    s_min = cv2.getTrackbarPos("SAT Min", "HSV")
    s_max = cv2.getTrackbarPos("SAT Max", "HSV")
    v_min = cv2.getTrackbarPos("VALUE Min", "HSV")
    v_max = cv2.getTrackbarPos("VALUE Max", "HSV")
    print(h_min)

    lower = np.array([h_min,s_min,v_min])
    upper = np.array([h_max,s_max,v_max])
    mask = cv2.inRange(imgHsv,lower,upper)
    result = cv2.bitwise_and(img,img, mask = mask)

    mask = cv2.cvtColor(mask, cv2.COLOR_GRAY2BGR)
    hStack = np.hstack([img,mask,result])
    cv2.imshow('Original', img)
    cv2.imshow('HSV Color Space', imgHsv)
    cv2.imshow('Mask', mask)
    cv2.imshow('Result', result)
    cv2.imshow('Horizontal Stacking', hStack)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
cv2.destroyAllWindows()

I am not sure whether this is the issue of OpenCV version, or anything related to the code or smth. Any ideas?

Answer 1

Possible Issue #1: Cam Settings

• Press Windows Key , type camera . Click on the Camera privacy settings .

  

• On the opening screen, make sure that Allow apps to access your camera is ON.

  

Now, retry with your code!

Possible Issue #2: Wrong index

Find the camera index:

max_cam_number = 10
for i in range(-1, max_cam_number):
    cap = cv2.VideoCapture(i)
    test, frame = cap.read()
    if test:
        print("i : "+str(i)+" /// result: "+str(test))

Most of the time, if you are using your laptop's webcam, you should try 0 :

cap = cv2.VideoCapture(0)