CODEWITHSUNDEEP
pythonopencv
Jesús González Rebordinos
Jesús González Rebordinos

Reputation: 47

Error using cv2.detectMultiScale() in a function called from another .py file

This is my first question here, so I hope I am asking it in the proper way.

I am running Python 3.6.3 (Anaconda 64-bit installation) on a laptop with Windows 10.

I have a main routine that, amongst other things, captures video via cv2.VideoCapture(). Another file stores a function to perform face detection. When I call the function from the main program I receive following error message: error: (-215) !empty() in function cv::CascadeClassifier::detectMultiScale

Here is a simplified version of the code:

Main program:

from facecounter import facecounter
import cv2

 cap = cv2.VideoCapture(0)

x = 0   
while x < 20:
    ret, frame = cap.read()
    print(type(frame))
    output = facecounter(frame, ret)
    cv2.imshow("output", output)
    cv2.waitKey()
    x += 1

cv2.destroyAllWindows()
cap.release()

Function stored in facecounter.py:

def facecounter(frame, ret):

    import cv2

    face_classifier = cv2.CascadeClassifier('cascades/haarcascade_frontalface_default.xml
    if ret is True:
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        faces = face_classifier.detectMultiScale(gray, 1.3, 5)
        number_faces = len(faces)

    return number_faces

I have search for this error and as far as I can see it is due to the lack of an appropriate image in numpy.array format fed to cv2.detectMultiScale(). So I tried to simplify even further the code to isolate the error:

Main routine:

from file import function

import cv2

cap = cv2.VideoCapture(0)

x = 0
while x<300:
    ret, frame = cap.read()
    output = file(ret, frame)
    cv2.imshow("window", output)
    print(output)

cv2.destroyAllWindows()
cap.release()

Function stored in file.py:

import cv2

def function(ret, frame):
    output = frame

    return output

When I run this simplified version of the code no error appears but, although for every iteration I get the correct array printed, the window created with cv2.imshow() shows a grey image.

I would really appreciate your help. Thanks a lot in advance!

Upvotes: 2

Views: 280

Answers (1)

fireant
fireant

Reputation: 14530

You need to fix your simplified version.

  1. the name of your function is function not file.
  2. you need to call cv2.waitKey(1).
  3. you're not incrementing x.

Here is the fixed code

from file import function

import cv2

cap = cv2.VideoCapture(0)

x = 0
while x<300:
    ret, frame = cap.read()
    output = function(ret, frame)
    cv2.imshow("window", output)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
    print(output)
    x += 1

cv2.destroyAllWindows()
cap.release()

Also it's not a good idea to name your python file file.py, name it image_processing.py or something that doesn't clash with names used by Python.

Upvotes: 1

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