@BigBen This sounds like you would be best looking for openCV's VideoCapture.open() questions? Maybe whatever it does requires certain files in certain places which are not present/found on the other system, either openCV runtime files or the file you are trying to open?

Hi and welcome to devnet, Are you sure you are linking all the required libraries ? Are they all from compatible compilers ?

@BigBen Yes, you always need to write a new class which derives from the base class if you need to override a virtual method, as QWidget::paintEvent(). The Analog Clock Example illustrates overriding paintEvent(). There will be hundreds of other examples online.

I am wondering whether there's some bad interaction between the 2017 build of Qt and your 2019 build of OpenCV. There should not as VS 2019 is backward compatible with 2017.

Hi and welcome to devnet, You can't jump from a 32bit float image to 16bit integer one like that. Convert your OpenCV image to 16 bit before making a QImage out of it.

Hi, You should check your video file, but as I wild guess, it's likely a FullHD video which is 1920 * 1024. Since you are creating a RGB QImage out of it, it's already weighing about 6MB per image. QPixmap is meant to be optimised for rendering and thus the backing memory used might even be larger for, for example, alpha channel handling. Depending on what else you do with your application and these images you can pretty quickly hit memory limits if your application is 32bit.

Lack INCLUDEPATH such as: INCLUDEPATH += /usr/local/include

Thank you all guys. Your suggestions and expert opinion helped a lot with solving the problem. QT forum is always so helpful. After trying many things here is the conclusion and code is now working perfectly fine I removed the tic toc part time(&start); timer = double(getTickCount()); tic(); It was working but crashing then just to make sure that QImage is not NULL I removed the img = QImage(); // releasing memory with if(!img.isNull()) img = QImage(); Its working perfectly fine now.

@Imran-Hassan said in QT image display is not working without declaring openCV namedWindow in windows 10: The problem is solved great, so please don't forget to mark your post as such!

I still don't know what exactly went wrong, but after I removed all of the OpenCV stuff and re-installed a fresh v4.1, it worked. So even though I checked all lib-files, there must have been something wrong with the linked libs (Pointing to different versions?! Links not working?!, etc.) Thanks @SGaist, your answer made me remove everthing and try the OCV version that is provided by Ubuntu 18.04. I got 3.X.X from there... After I removed this version again (because I want a newer one) and installed 4.1 from OCV page, it worked :-)

@jsulm Hello! Sorry, but that doesn't work. I tried to insert a loop in different places, but the result remains the same. I also tried to display the main widget. @SGaist Hello. So the VideoWindow.h file (VideoWindow class) is my custom widget. This is the first piece of code that I presented.

@jsulm said in QDataStream an openCV::mat serialisation...: @Dariusz What is stream here? Is it QDataStream? "Any idea what did I mess up with this ?" - well, what is not working? Yep :- ) I think I might "got it". Naturally 5 min after asking question... elemSize1() return incorrect number of channels. Looks like I need elemSize() instead. still testing. Yep it was wrong element number. Hope it helps other "serializers" out here : -)

@r-p-h said in OpenCV 4.1.1 Imread() & Imwrite() Crashes Program ?: now everything is working fine. so please don't forget to mark your post as solved! Thanks.

An update on this. It works perfectly and its a very low-cost solution. My processing time remains almost the same (~10mS) using this method since the painter does the scaling for you when it draws. Thanks for your help guys.

@chris1092387456 could it be possible you have mixed Qt versions from the one you cross-compiled and the one it's used by the OpenCV install script you used. Assuming you run Ubuntu/opencv_latest.sh which in turn calls opencv_install.sh and then dependencies.sh, there are some apt-get install calls, so you''ll end up having pre-built Qt libraries along with your cross-compiled ones... function install_dependency { echo "--- Installing dependency: $1" sudo apt-get -y install $1 } ... install_dependency libqt5x11extras5 install_dependency libqt5opengl5 install_dependency libqt5opengl5-dev So may I suggest to start from scratch? First I'd follow the mechatronics guide to cross-compile and deploy Qt in the RPi device. Then I'd follow this guide to cross compile the latest version of OpenCV for Raspberry Pi. As you'll use WITH_QT=ON flag I guess, please adjust the paths in the CMake script(s) to use the cross-compiled Qt version in your host PC. And also use the correct path for cross-compiled OpenCV in your .pro file. As example, the following doesn't look good to me: LIBS += -L/usr/local/lib/libopencv_highgui.so

@Gojir4 thanks, I am trying that right now. I’ve added a 1s delay in my image grabbing thread. Let’s see. Fingers crossed!

@JKSH This is how I emit the OpenCV mat data: emit processedImage(2, videoFrameOut.ptr(0,0),videoFrameOut.cols, videoFrameOut.rows, videoFrameOut.step); The first parameter is just used to determine which display should draw the image and the rest are dimensions and stride which I think are ok. @SGaist You are correct, I changed the line below to make a copy: displayImage = QImage(imageData, width, height, step, QImage::Format_RGBA8888).copy(0,0,width,height); I think this fixed the issue. I got a couple of crashes in 'memcpy' but that was when loading files a little too quickly. I think most likey resizing the data quickly was the issue. I will do more testing this week and post the results. UPDATE: I did a lot more testing and making a local copy fixed the issue. The issue was that I was modifying the array before it was fully copied and this caused crashes when the array was downsized. I will need to revise the overall structure to make sure everything is done sequentially. Thanks!

Thank you for your answer! I've yet to find a good introduction into QML for C++ developers, but I was a little put off by the somewhat convoluted approach as different tutorials either don't show any QML or only use it soley to develop a very simple application. The main problem I'm struggling is with QML is the ability to generate a GUI based on some set preferences. In my case the amount of e.g tabs in the "Options" pane should be defined by the amount of video files which are currently loaded. Is this easily possible to programatically extend QML GUIs?

Then add a signal to your dialog that you will emit when needed from your mouse move event.

Problem Solved: '/' not '\' in .pro file AND run qmake after change. I tried changing '\' to '/' but didn't run qmake.

Hi and welcome to devnet, Can you show the code you are using ? What exactly do you expect ? What exactly do you get ?

@sierdzio said in QWidget: Cannot create a QWidget without QApplication - OpenCV imshow() 2.4.13 ?: Is Qt the only supported backend? If yes, then indeed requirements do propagate. No, it has been added later on. It's maybe even the latest that has been implemented. AFAIK, what the OP is hitting here, is that OpenCV doesn't have an implementation for imgshow for iOS. It would require to either use Qt to show the result of what he's doing or native stuff.

Yeah i feel like i do sudo apt-get update && upgrade at least once a day. I just checked about SIP and i compiled it from source but i cant remember if i actually used the command make and make install. Does that mean i have to reinstall pyqt5 again? I guess i just open a new thread. Thanks for all the help @SGaist

Hi, GStreamer in OpenCV ? Shouldn't you rather post this question on either or maybe both of their forum ?

@Chris-Kawa Thank you, now it works. The solution was simple, but apparently I must understand better how the paths work. If you have any advice on where to start reading or you know any interesting online article/tutorial, please tell me :-)

Hi, Maybe a silly question but are you sure that OpenCV is properly installed in opencvArm ?

dll paths do not influence the build so they are not included in qmake. if you use QtCreator in the right bar select project and in the build and run tab, select the run subtab and you can customise the run environment adding the paths of the dlls to the run environment PATH otherwise you can use the INSTALLS of qmake to deploy all the binaries where you need them

Hi, Just a quick note, taking a look at fixing this "fix", I just saw that the latest version of the contrib repository doesn't contain the offending code anymore.

@Sam_ I'm glad i could help. Please mark the Thread as "solved" if it's solved for you. :)

hello, here is a working example https://goo.gl/2puvC1

Good ! In that case, please mark the thread as solved using the "Topic Tool" button so that other forum users may know a solution has been found :)

@SGaist yes all opencv files is included in the path. After some research in log file, i think I have a problème with the génération of libopencv_imgcodecs310 and libopencv_imgproc310 files. I'll keep you posted.

@SGaist said: Android Hello all, Sorry for the late reply As SGaist said i was able to build and run qt with opencv successfully on windows desktop using mingw for desktop bundled with qt for android Thanks Amal

As it is not related to Qt you should ask OpenCV community.

Take a look at the answer here