OpenCV: how to force the image window to appear on top of other windows?

Question

Using cvShowImage, one can easily show an image in OpenCV. However, how do you tell OpenCV to show the window on top of every other window?

I run a full screen OpenGL application while showing images. The first time the OpenCV window pops up on top of my application window, but if I click on the window of my application (i.e. give focus back to it), then I can't manage to have the OpenCV come back on top of the OpenGL window, even when destroying and recreating the window.

I thought of renaming the window each time, but is there another way to do it?

Answer 1

Beginning with OpenCV releases 3.4.8 and 4.1.2, setWindowProperty has a WND_PROP_TOPMOST property that you can set. Example Python code:

import cv2 import numpy as np  window_name = "image" img = np.zeros([480, 640, 1]) cv2.imshow(window_name, img) cv2.setWindowProperty(window_name, cv2.WND_PROP_TOPMOST, 1) cv2.waitKey(0) 

Answer 2

OK, I figured it out which works for both OSX and Windows. You just need to create a full-screen window and show it for a very short time, then your next window from OpenCV will be in front. So, first to open a full-screen window:

cv::namedWindow("GetFocus", CV_WINDOW_NORMAL); cv::Mat img = cv::Mat::zeros(100, 100, CV_8UC3); cv::imshow("GetFocus", img); cv::setWindowProperty("GetFocus", CV_WND_PROP_FULLSCREEN, CV_WINDOW_FULLSCREEN); waitKey(1); cv::setWindowProperty("GetFocus", CV_WND_PROP_FULLSCREEN, CV_WINDOW_NORMAL); destroyWindow("GetFocus"); 

And then you can open up anther window that actually show the image:

Mat your_image = ...; cv::namedWindow("ShowImg"); cv::imshow("ShowImg", your_image); 

It works for me.