Display image sequence

vein

Hello everybody,
I am currently working on an application which uses Qt, OpenCV and dlib to load a movie, split it into frames and analyze the frames via face detection.
I am able to compute the movie into frames and apply the face detection on each individual frame.
The problem is that I want to display the computed images - which are augmented with a bounding box around the detected faces - but I am not able to change the displayed image in the Graphicsview/ Graphicsscene.
Here is the constructor of my main class (the imageView member references the *QGraphicsView *item constructed in the Qt UI Creator):

qt_3::qt_3(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);

    imageScene = new QGraphicsScene(this);
    imageScene->setSceneRect(0, 0, ui.imageView->width(), ui.imageView->height());

    ui.imageView->setScene(imageScene); // the QGraphicsView item
    ui.imageView->fitInView(imageScene->sceneRect(), Qt::KeepAspectRatio);

    connect(&faceDetector, SIGNAL(signalImage()), this, SLOT(on_displayImage()));
}

The imageScene is declared like this in the header file:

private:
Ui::qt_3Class ui;
QGraphicsScene *imageScene;

Here is the method which gets called when the face detection algorithm generated a new image:

void qt_3::on_displayImage(){
    Mat image = faceDetector.getComputedImage();

    if(!image.data){
	    Functions::LogStr("Failed to display image");
	    return;
    }else{
	    Functions::LogStr("Display image");

	    Mat temp;
	    cvtColor(image, temp, CV_BGR2RGB); 
	    QImage qImage((const uchar *) temp.data, temp.cols, temp.rows, temp.step, QImage::Format_RGB888);
	    qImage.bits();
	
	    imageScene->clear();

	    imageScene->addPixmap(QPixmap::fromImage(qImage));
	    imageScene->update();
	    ui.imageView->update();
    }
}

When the on_displayImage method is invocted nothing happens, the scene does not even get cleared (I loaded up a test image in the constructor which is displayed fine).
I would like to thank you very much for your answers and appreciate the help!

SGaist

Hi and welcome to devnet,

Are you sure that temp does contain a valid image ?

vein

Hi,
first of all thank you very much for your answer.
I checked if the image is valid via QImage's method isNull and I also checked the Mat object's data before it ist converted, both state that the image data is correct. What confuses me is that the scene is not even cleared; I also tried to load a static image in the on_displayImage method but nothing gets cleared or displayed.

SGaist

Did you try to move your image at the center of the scene ?

vein

@SGaist
Thanks for the answer.
I positioned the image at the center of the scene and I also ensured that the scene is active - which it is. It seems that all changes at the scene have no visible effect.

SGaist

Might be a silly question but are you sure that the getComputedImage function returns a new image each time you call it ?

vein

@SGaist
I checked if a new image was returned by saving each image data to a file before it gets returned and the image seems to be correct.
I will try to replace the graphicsview/scene by a QLabel, perhaps this will work.