cv2.waitkey（1）没有在opencv python中运行

Question

I need to understand cv2.waitkey() in python with cv2

faceCascade = cv2.CascadeClassifier(cascPath)

video_capture = cv2.VideoCapture(0)

while True:
    # Capture frame-by-frame
ret, frame = video_capture.read()

gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

faces = faceCascade.detectMultiScale(
    gray,
    scaleFactor=1.1,
    minNeighbors=8,
    minSize=(40, 40),
    #flags=cv2.cv.CV_HAAR_SCALE_IMAGE
    flags = 0
)   

# Draw a rectangle around the faces
for (x, y, w, h) in faces:
    cv2.rectangle(gray, (x, y), (x+w, y+h), (0, 255, 0), 2)

# Display the resulting frame
cv2.imshow('Video', gray)
if cv2.waitKey(1) & 0xFF == ord('q'):
    break
if cv2.waitKey(1) & 0xFF == ord('b'):
    cv2.imwrite('example.png',gray)

cv2.waitKey() when I press b it doesn't save picture but press q works . Please help!

Answer 1

You are calling waitKey() twice. With your code, press any key but q then press b and it will save the image.

Only call waitKey(1) once, and save the result in a variable, then test that variable, eg:

keypress = cv2.waitKey(1)
if keypress & 0xFF == ord('q'):
    break
if keypress & 0xFF == ord('b'):
    cv2.imwrite('example.png',gray)