QAbstractVideoSurface camera frames brightness

[tomatoketchup]

Hi everyone,

I implemented a QAbstractVideoSurface, and a widget to be painted based on this example.
Everything works fine, but the camera preview I get is very dark compared to the result I get when I use a QCameraViewfinder or QVideoWidget.
Here's the code I am using to create the QCamera:

m_camera = new QCamera(this);

connect(m_camera, &QCamera::statusChanged, this, &MainWindow::cameraStatusChanged);

m_camera->load();
m_camera->setViewfinder(ui->videoWidget->videoSurface()); // videoSurface is a QAbstractVideoSurface

And here's the slot 'cameraStatusChanged':

void MainWindow::cameraStatusChanged(QCamera::Status status)
{
    if(status == QCamera::LoadedStatus)
    {
        m_cameraLoaded = true;

        QCameraImageProcessing *imgProcessing = m_camera->imageProcessing();

        if(imgProcessing->isAvailable())
        {
            qDebug() << "image processing available";
            imgProcessing->setBrightness(1.0);
            imgProcessing->setSaturation(1.0);
        }
    }
    else if(status == QCamera::UnloadedStatus)
    {
        m_cameraLoaded = false;
    }
}

Unfortunately, the brightness and the other filters (like the saturation) don't work and the preview video is still dark.

How can I change the brightness of my video frames?
Do I need to implement my own QVideoWidget and a QPainterVideoSurface (which is undocumented) ?
Thank you in advance.

EDIT: Is there a way to adjust the brightness automatically, as the QVideoWidget does?

[tomatoketchup]

For those who implemented a QAbstractVideoSurface: didn't anyone have that problem?