QPixmap or QImage for JFIF image format

[scottnat]

Hi all, I have some incoming image data from a camera that is in JFIF APP0 format.
The first four bytes are: 0xFF, 0xD8, 0xFF, 0xE9.

Which what I see from https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format (JFIF APP0 marker segment).

Problem: Looking through the docs, I am unable to find anything that supports JFIF. As the header formats are different than JPEG, I was wondering if anyone has any recommendations on a workaround with either using QPixmap or QImage?

Alternative: I could also retrieve image data as raw matrix (mat) form and use OpenCV methods, however i was unable to build opencv for my QT 5.1, MSVC2015 64 bit.

Goal 1: Display image on QLabel or QGraphicsView.
Goal 2: Video from sequence of images.

Thanks and hoping to hear from you.

[SGaist]

Hi,

Did you try to force the use of the JPEG plugin to read the image ?
Can you provide a sample image in that format ?

[scottnat]

@SGaist Hi yes, I was able to force the JFIF format and found a solution to display my image on a QLabel.

I was wondering now, how would I be able to play a sequence of images onto the QLabel, like an animation/video.

    for(int x=0;x<10;x++){ //GET 10 IMAGES INTO QList<QPixmap>
        
        BYTE* cameraImage = new BYTE[dwMaxImageBytes];
        DWORD dwImageBytes;
        CaptureImage(cameraImage, dwMaxImageBytes, &dwImageBytes); //API for getting JFIF image
        
        QPixmap pix;
        pix.loadFromData((const uchar*)cameraImage,dwImageBytes,"JFIF");
        *qpixmaplist << pix; //declared in header file as QList<QPixmap>* qpixmaplist
    }

    timer.setInterval(1000); //attempting to display one image on a QLabel every 1 sec
    connect(&timer,SIGNAL(timeout()),this,SLOT(procPixmap()));
    timer.start();

The procPixmap slot:

void MainWindow::procPixmap(){
    if(pixcounter>=10){
        timer.stop();
        disconnect(&timer,SIGNAL(timeout()),this,SLOT(procPixmap()));
    }
    else{
        ui->label->setPixmap(qpixmaplist->at(pixcounter));
        pixcounter++;
    }
}

[SGaist]

Something is not clear, do you want to get the images from the camera or from files to show that "video" ?

[scottnat]

@SGaist
Thanks for the reply. Basically, from a camera's API "CaptureImage", i store one image in an array of unsigned char bytes.

CaptureImage(cameraImage, dwMaxImageBytes, &dwImageBytes); 

That one image is loaded as a QPixmap, and fed to a QList of QPixmaps.

QPixmap pix;
pix.loadFromData((const uchar*)cameraImage,dwImageBytes,"JFIF");
qpixmaplist << pix; 

Now, everything works. My images are displayed at a rate determined by the timer interval.

However, is there a cleaner way to convert these QList <QPixmap> into a more video format, rather than having to physically update images, like a script boy on a TV set.
ui->label->setPixmap(qpixmaplist[counter]); counter++;

[SGaist]

How fast are these images coming ?

[scottnat]

@SGaist
Thanks for the reply. For me:

• Each call to the CaptureImage API takes approximate 6 ms.
• Loading to the QList<QPixmap> takes an additional 90 ms.

[SGaist]

Why create a QList and not do the conversion directly after calling CaptureImage ?

Otherwise, does the library you are using to get the image provide a streaming API ?