What does OpenCV's cvWaitKey( ) function do?

c++ c opencv
Simplicity picture Simplicity · Mar 7, 2011 · Viewed 148.4k times · Source

What happens during the execution of cvWaitKey()? What are some typical use cases? I saw it in OpenCV reference but the documentation isn't clear on its exact purpose.

Answer

SuperElectric picture SuperElectric · Aug 5, 2011

cvWaitKey(x) / cv::waitKey(x) does two things:

  1. It waits for x milliseconds for a key press on a OpenCV window (i.e. created from cv::imshow()). Note that it does not listen on stdin for console input. If a key was pressed during that time, it returns the key's ASCII code. Otherwise, it returns -1. (If x is zero, it waits indefinitely for the key press.)
  2. It handles any windowing events, such as creating windows with cv::namedWindow(), or showing images with cv::imshow().

A common mistake for opencv newcomers is to call cv::imshow() in a loop through video frames, without following up each draw with cv::waitKey(30). In this case, nothing appears on screen, because highgui is never given time to process the draw requests from cv::imshow().

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