Assertion failed error in cv::CascadeClassifier::detectMultiScale in openCV

Question

I'm running on my python code using openCV

import cv2
import numpy as np

cap = cv2.VideoCapture(0)

face = cv2.CascadeClassifier('haarcascade_frontalface_alt.xml')

while 1:
    ret, frame = cap.read()         ##Read image frame
    frame = cv2.flip(frame, +1)     ##Mirror image frame
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    detect_face = face.detectMultiScale(gray, 1.2, 1)
    for(x, y, z, h) in detect_face:
        cv2.rectangle(frame, (x, y), (x+z, y+h), (0, 255, 0), 2)
        ROI = gray[x:x+z, y:y+h]
        length = ROI.shape[0]
        breadth = ROI.shape[1]
        Area = length * breadth
        display = 'Area = ' + str(Area)
        if Area > 0:
            cv2.putText(frame, display, (5, 50), font, 2, (255, 255, 0), 2, cv2.LINE_AA)

    for(x, y, z, h) in detect_face:
        cv2.rectangle(frame, (x, y), (x+z, y+h), (0, 255, 0), 2)
        ROI = gray[x:x+z, y:y+h]
        length = ROI.shape[0]
        breadth = ROI.shape[1]
        Area = length * breadth
        Distance = 3 * (10 ** (-9)) * (Area ** 2) - 0.001 * Area + 108.6
        display = 'Distance = ' + str(Distance)
        if Area > 0:
            cv2.putText(frame, display, (5, 50), font, 2, (255, 255, 0), 2, cv2.LINE_AA)

it prompted that

penCV(4.4.0) C:\Users\appveyor\AppData\Local\Temp\1\pip-req-build-71670poj\opencv\modules\objdetect\src\cascadedetect.cpp:1689: error: (-215:Assertion failed):empty() in function 'cv::CascadeClassifier::detectMultiScale'

I don't understand why this continuously happened. I followed all instruction given from this site http://art-of-electronics.blogspot.com/2020/06/how-far-you-are-from-your-camera-python.html and I still could not figure it out.

Answer 1

it says that image is empty, so probably you're not correctly loading the image or importing the frame from the camera.

Make sure your path to the cascade file is correct. It fixed that for me.

• check if the spellings specified is correct

• if the cascade is inside a folder specify that too

• check for typos

• check the index of the camera provided

hope you get it fixed regards