How to create a counter in face detection?

Question

As you can see in the code below, it only detects the faces with haar cascade, I would like to know how I show the webcam how many people are currently detected. For example, show in the corner of the webcam X people detected.

from  __future__ import print_function 
import cv2 
cap = cv2.VideoCapture(0) 

face_cascade = cv2.CascadeClassifier("haarcascade_frontalface_default.xml")

while (cap.isOpened()):
   ret,frame = cap.read()
   gray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)

faces = face_cascade.detectMultiScale(gray, scaleFactor=1.3, minNeighbors=5, 
flags=cv2.CASCADE_SCALE_IMAGE,minSize=(50, 50), maxSize=None)

if len(faces) > 0:
  print("detected person!")
for (x, y, w, h) in faces:
    cv2.rectangle(frame, (x - 10, y - 20), (x + w + 10, y + h + 10), (0, 255, 0), 2)
    roi_gray = frame[y-15:y + h+10, x-10:x + w+10]

cv2.imshow("imagem", frame) 
if cv2.waitKey(1) & 0xFF == ord('q'): 
break 

cap.release() 
cv2.destroyAllWindows()

score 1 · Answer 1 · answered Jun 04 '18 at 03:20

I suspect everything shown in the code works just fine.

If so, you already know how many faces are detected with len(faces). You now only need to add this info into the video.

For this, I suggest you use the cv::putText function : https://docs.opencv.org/3.1.0/d6/d6e/group__imgproc__draw.html#ga5126f47f883d730f633d74f07456c576

You will then be able to add this on each frames that are read.

Side note: This might just be because of copy-pasting your code here, but pay attention to your indentation.

score 0 · Accepted Answer · answered Jun 04 '18 at 08:22

Simply displaying the count of len(faces) may not solve the purpose,as you can have instances wherein there are multiple bounding boxes drawn over the same face.Therefore, I would suggest you to perform Non Maximal Suppression(NMS) on the result of your detections, followed by incrementing a counter for each time one calls the NMS operation. The final count of the counter will give you a better and more accurate result.

How to create a counter in face detection?

2 Answers2