I'm trying to use the function detectMultiScale() but it shows me Bad Argument error

Question

import cv2 as cv
img=cv.imread('photo/goku3.jpg')
cv.imshow('image', img)

gray=cv.cvtColor(img, cv.COLOR_BGR2GRAY)
cv.imshow('gray', gray)

haar_cascade=cv.CascadeClassifier('faces.xml')
faces_rect=haar_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbours=3)
print(f"Number of faces found = {len(faces_rect)}")

for (x,y,w,h) in faces_rect:
    cv.rectangle(img, (x,y), (x+w,y+h), (0,255,0), thickness=2)

cv.imshow('detected face', img)
cv.waitKey(0)

Traceback (most recent call last):
  File "e:\imageRecognitionProj\faceDetect.py", line 9, in <module>
    faces_rect=haar_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbours=3)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cv2.error: OpenCV(4.7.0) :-1: error: (-5:Bad argument) in function 'detectMultiScale'
> Overload resolution failed:
>  - 'minNeighbours' is an invalid keyword argument for CascadeClassifier.detectMultiScale()
>  - 'minNeighbours' is an invalid keyword argument for CascadeClassifier.detectMultiScale()

inside the haar_cascade variable i have defined the cascadeClassifier() with the xml file

I think the function detectMultiScale() is not available. I tried to reinstall open-cv but it didn't worked.

Answer 1

The issue is just a spelling mistake:
Replace minNeighbours=3 with minNeighbors=3.

The error message means that there is no version of detectMultiScale() method that has an argument named minNeighbours (but that the method exists with other names of arguments).

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Regarding the availability of detectMultiScale():

Make sure you don't have packages that my conflicted - opencv-python-headless and opencv-python, but only have opencv-contrib-python package installed.
If this is not the case, you may uninstall the packages or use new virtual environment.
If not exist, install by executing: pip install opencv-contrib-python.
(Note that according to the error message the package is installed).

I couldn't find faces.xml, and used haarcascade_frontalface_default.xml instead.

Code sample:

import cv2 as cv
img=cv.imread('photo/goku3.jpg')
cv.imshow('image', img)

gray=cv.cvtColor(img, cv.COLOR_BGR2GRAY)
cv.imshow('gray', gray)

#haar_cascade=cv.CascadeClassifier('faces.xml')
haar_cascade=cv.CascadeClassifier(cv.data.haarcascades + "haarcascade_frontalface_default.xml")  #https://stackoverflow.com/a/59717885/4926757

#faces_rect=haar_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbours=3)
faces_rect=haar_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbors=3)
print(f"Number of faces found = {len(faces_rect)}")

for (x,y,w,h) in faces_rect:
    cv.rectangle(img, (x,y), (x+w,y+h), (0,255,0), thickness=2)

cv.imshow('detected face', img)
cv.waitKey(0)

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img (example):