python - OpenCV 2 raising exceptions on read() with different resolutions -

what might reasons of cv2.videocapture.read() exception?

i have app shows live feed of camera (preview frames) , after button press takes snapshot higher resolution.

the preview frames, @ 640x360 read no problems, after running time starts raise exceptions whenever try retrieve image 1920x1080 resolution.

exception: null object passed py_buildvalue.

ok

.set(3, 640) .set(4, 360) 

error

.set(3, 1920) .set(4, 1080) 

cam.read() can't return false in tuple, crashes.

related code:

  # timer   self.timer = qtimer()   self.timer.timeout.connect(self.__countdown)   self.timer.start(100)  def __countdown(self):   self.__grabframe()   if self.counter == 1:     # show background image   elif self.counter % 10 == 0:     # show countdown on screen   elif self.counter == 29:     self.timer.stop()     self.counter = 0     self.camcapture.set(3, 1920)     self.camcapture.set(4, 1080)     self.__takepicture()   self.counter += 1  def __grabframe(self):   # grab frame, transform image , display inside pixmap   # used show video screen while counting down taking place   frame = self.camcapture.read()   image = qimage(frame[1].data, 640, 360, qimage.format_rgb888).rgbswapped()#.mirrored(true, false)   self.pixmap = qpixmap.fromimage(image)   self.background.setpixmap(self.pixmap)  def __takepicture(self):   # grab frame, transform image , display inside pixmap   try:     frame = self.camcapture.read()     self.logger.info("[takepicture] retval camcapture.read(): {0}".format(str(frame[0])))     image  = qimage(frame[1].data, 1920, 1080, qimage.format_rgb888).rgbswapped()     pixmap = qpixmap.fromimage(image)     self.pixmap = pixmap   except exception e:     self.logger.error("[takepicture] {0}".format(str(e)))