How to check if these is no face detected using cvlib

Question

cvlib library in python is well established and many people in research community uses it. I noticed that if threr is no face detected the (for) loop stops for exampe, if i have the following code:

cap = cv2.VideoCapture(0)
if not (cap.isOpened()):
    print('Could not open video device')
#To set the resolution
vid_height = cap.get(cv2.CAP_PROP_FRAME_HEIGHT)
vid_width = cap.get(cv2.CAP_PROP_FRAME_WIDTH)
while(True):
    ret, frame = cap.read()
    if not ret:
        continue
    faces, confidences = cv.detect_face(frame)
    # loop through detected faces and add bounding box
    for face in faces:
        (startX,startY) = face[0],face[1]
        (endX,endY) = face[2],face[3]
        cv2.rectangle(frame, (startX,startY), (endX,endY), (0,255,0), 2)
        crop_img = frame[startY-5:endY-5, startX-5:endX-5]```
        print(faces)
        cv2.imshow('object detected',frame)
    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break
cap.release()
cv2.destroyAllWindows()

as Im printing (faces) the output would be somthing like this

[[392, 256, 480, 369]]
[[392, 256, 478, 369]]
[[392, 255, 478, 370]]
.
.
.
[[392, 255, 478, 370]]

However, as soon as I block the camera or move my head away from it, as there is no face detected, the for loop freezes or pauses till it sees a face to detect.

I need an if statement or any other condition to check this freeze or a pause to produce do something else.

James_64_64 · Accepted Answer · 2020-04-09T11:15:05.773

1

I have found the answer to this question if we add an if statement before the for loop as faces is an int produces 1,2,3 depending on how many faces in front of the camera.

if len(faces) == 0:
   print('no faces')
   print(faces) # going to print 0
else:
   for face in faces:
       (startX,startY) = face[0],face[1]
       (endX,endY) = face[2],face[3]
       crop_img = frame[startY-5:endY-5, startX-5:endX-5]
       cv2.rectangle(frame, (startX,startY), (endX,endY), (0,255,0), 2)
    cv2.imshow('object detected',frame)

    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break
cap.release()
cv2.destroyAllWindows()

edited Apr 09 '20 at 11:15

answered Apr 09 '20 at 11:09

James_64_64

11
3

thank you for your answer you helped me a lot but I advise you to comment your code to make it easier for others to read thank you – sabayke bremso Nov 19 '22 at 08:53

score 0 · Answer 2 · answered Apr 09 '20 at 06:10

You are displaying only the frames where face is detected. If no face is detected you are seeing the last frame where face is detected until the next time a face is detected in the coming frames.

Move the imshow out of for loop. For example,

# loop through detected faces and add bounding box
for face in faces:
    (startX,startY) = face[0],face[1]
    (endX,endY) = face[2],face[3]
    cv2.rectangle(frame, (startX,startY), (endX,endY), (0,255,0), 2)
    crop_img = frame[startY-5:endY-5, startX-5:endX-5]
    print(faces)

cv2.imshow('object detected',frame)
k = cv2.waitKey(30) & 0xff
if k == 27:
    break

Checkout the complete example here.

Hi @Arun Ponnusamy, I am glad you replyed to my question, tbh this was a typo and in my actual code it is written out side of the loop, the issue is how can i say ok these is a face or there is not because as i block the camera with my hand everything stops and no outcome appears. I tried to add this out side of the (for) loop if len(faces) == 0: — James_64_64, Apr 09 '20 at 10:56

How to check if these is no face detected using cvlib

2 Answers2