Count number of detections with OpenCV lib with Python

Question

I have started to learn OpenCV lib in Python. I want to write a code that will detect faces and eyes on the photo but also count number of detections. I have wrote a picture that has 6 people on it. You can download the image form here:

https://www.sendspace.com/file/cznbqa

I wrote a code that detect faces and eyes, but I do not know how to count number of detections. Also, my code detect 4/8 faces and 1/12 eyes on the photo so...I probably have some issues in the code, If you can help me with that also, I would be very thankful.

 # Standard imports

import cv2
import numpy as np

# Read image
my_image = cv2.imread("ljudi.jpg", 1)

# data for detecting faces and eyes
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_alt.xml')
eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')


img = cv2.imread("ljudi.jpg", 1)
gray = cv2.cvtColor(img, 0)

faces = face_cascade.detectMultiScale(gray, 1.2, 4)

for (x,y,w,h) in faces:

    #detect face with bule rectangle
    #rec. start point (x,y), rec. end point (x+w, y+h), blue color(255,0,0), line width 2
    face_rec = cv2.rectangle(img, (x,y), (x+w, y+h), (255,0,0), 1)        

    roi_gray = gray[y:y+h, x:x+w]
    roi_color = img[y:y+h, x:x+w]

    eyes = eye_cascade.detectMultiScale(roi_gray, 1.1, 2)

    for (ex,ey,ew,eh) in eyes:

        eye_rec = cv2.rectangle(roi_color, (ex,ey), (ex+ew, ey+eh), (0,255,0), )

cv2.imshow('img', img)
cv2.waitKey(0)

len(faces) (and len(eyes) respectively) does not do what you need? — handle
– handle, Commented Oct 11, 2019 at 12:00
I've added this trivial info as answer just so this problem can be marked as solved.. — handle
– handle, Commented Oct 12, 2019 at 8:54

handle · Accepted Answer · 2019-10-12 08:53:25Z

1

From the OpenCV documentation:

https://www.docs.opencv.org/2.4/modules/objdetect/doc/cascade_classification.html#cascadeclassifier-detectmultiscale

Detects objects of different sizes in the input image. The detected objects are returned as a list of rectangles.

where a rectangle for the Python bindings simply seems to be of type list [x,y,w,h] (https://www.docs.opencv.org/2.4/modules/core/doc/basic_structures.html#rect).

To the number of faces / rectangles returned inside the list can easily be retrieved by getting the length of the list (i.e. number of items inside), which is done with the Python builtin function len(): https://docs.python.org/3/library/functions.html#len.

answered Oct 12, 2019 at 8:53

handle

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2 Comments

taga Over a year ago

Thanks, can you maybe help me with this question also? stackoverflow.com/questions/58349314/…

handle Over a year ago

@taga Sorry, have not used those libraries yet.

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