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Thread: How to display opencv output window inside a Label or Widget in form.ui

  1. #1
    Join Date
    Feb 2017
    Qt products

    Default How to display opencv output window inside a Label or Widget in form.ui

    Hi all,

    I am new to Qt and opencv, I am programming a graphical interface to record a video through webcam using opencv libraries in Qt. Problem is when I push the start recording button on my interface, a new window gets launched and I dont want that. It should be like after pressing the start recording button it should display the opencv output of webcam inside a Label or Widget on my graphical interface and not on a newly launched window.

    I am using Qt 5.8 on windows 10. Below is the while loop which captures the frame and displays in a window:

    Qt Code:
    1. while (1)
    2. {
    4. Mat frame;
    6. bool bSuccess =; // read a new frame from video
    8. if (!bSuccess)
    9. {
    10. cout << "ERROR: Cannot read a frame from video file" << endl;
    11. break;
    12. }
    14. oVideoWriter.write(frame);
    17. imshow("MyVideo", frame); //this line launches a new output window
    20. if (waitKey(10) == 27)
    21. {
    23. cout << "esc key is pressed by user" << endl;
    24. return ;
    26. }
    27. }
    To copy to clipboard, switch view to plain text mode 

    Can anyone please guide me on the code of how can I embed the opencv output window inside a Label or Widget in my form.ui.

    Thank you for your time and knowledge.

  2. #2
    Join Date
    Jan 2006
    Munich, Germany
    Thanked 418 Times in 411 Posts
    Qt products
    Qt3 Qt4 Qt5 Qt/Embedded
    Unix/X11 Windows

    Default Re: How to display opencv output window inside a Label or Widget in form.ui

    Back in the day I was doing such things using QImage and QPixmap.
    Have a look at the documentation of both classes, ask if you have any further questions.
    ==========================signature=============== ==================
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    Do you write clean code? - if you are TDD'ing then maybe, if not, your not writing clean code.

  3. #3
    Join Date
    Jan 2008
    Alameda, CA, USA
    Thanked 773 Times in 763 Posts
    Qt products
    Windows Android

    Default Re: How to display opencv output window inside a Label or Widget in form.ui

    And don't use infinite while() loops in Qt applications without also calling QCoreApplication::processEvents() somewhere within it. Otherwise, your application GUI will lock up. All GUI updates in Qt depend on having an event loop that that can process events (like painting); if you write an infinite while() loop that doesn't let this processing occur, then even if your loop is retrieving frames and updating an image to be displayed on a label, the label will never have chance to repaint itself.
    <=== The Great Pumpkin says ===>
    Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

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