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Check return value in python tutorial

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This commit is contained in:
LaurentBerger 2019-02-20 14:38:57 +01:00
parent 3bba5b5a31
commit 4ebb617000
1 changed files with 28 additions and 20 deletions
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48
doc/py_tutorials/py_gui/py_video_display/py_video_display.markdown
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@ -25,23 +25,27 @@ import numpy as np
import cv2 as cv import cv2 as cv
cap = cv.VideoCapture(0) cap = cv.VideoCapture(0)
if not cap.isOpened():
while(True): print("Cannot open camera")
exit()
while True:
# Capture frame-by-frame # Capture frame-by-frame
ret, frame = cap.read() ret, frame = cap.read()
# if frame is read correctly ret is True
if not ret:
print("Can't receive frame (stream end?). Exiting ...")
break
# Our operations on the frame come here # Our operations on the frame come here
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY) gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
# Display the resulting frame # Display the resulting frame
cv.imshow('frame',gray) cv.imshow('frame', gray)
if cv.waitKey(1) & 0xFF == ord('q'): if cv.waitKey(1) == ord('q'):
break break
# When everything done, release the capture # When everything done, release the capture
cap.release() cap.release()
cv.destroyAllWindows() cv.destroyAllWindows()@endcode
@endcode
`cap.read()` returns a bool (`True`/`False`). If frame is read correctly, it will be `True`. So you can `cap.read()` returns a bool (`True`/`False`). If frame is read correctly, it will be `True`. So you can
check end of the video by checking this return value. check end of the video by checking this return value.
@ -75,13 +79,17 @@ import cv2 as cv
cap = cv.VideoCapture('vtest.avi') cap = cv.VideoCapture('vtest.avi')
while(cap.isOpened()): while cap.isOpened():
ret, frame = cap.read() ret, frame = cap.read()
# if frame is read correctly ret is True
if not ret:
print("Can't receive frame (stream end?). Exiting ...")
break
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY) gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
cv.imshow('frame',gray) cv.imshow('frame', gray)
if cv.waitKey(1) & 0xFF == ord('q'): if cv.waitKey(1) == ord('q'):
break break
cap.release() cap.release()
@ -123,20 +131,20 @@ cap = cv.VideoCapture(0)
# Define the codec and create VideoWriter object # Define the codec and create VideoWriter object
fourcc = cv.VideoWriter_fourcc(*'XVID') fourcc = cv.VideoWriter_fourcc(*'XVID')
out = cv.VideoWriter('output.avi',fourcc, 20.0, (640,480)) out = cv.VideoWriter('output.avi', fourcc, 20.0, (640, 480))
while(cap.isOpened()): while cap.isOpened():
ret, frame = cap.read() ret, frame = cap.read()
if ret==True: if not ret:
frame = cv.flip(frame,0) print("Can't receive frame (stream end?). Exiting ...")
break
frame = cv.flip(frame, 0)
# write the flipped frame # write the flipped frame
out.write(frame) out.write(frame)
cv.imshow('frame',frame) cv.imshow('frame', frame)
if cv.waitKey(1) & 0xFF == ord('q'): if cv.waitKey(1) == ord('q'):
break
else:
break break
# Release everything if job is finished # Release everything if job is finished