Camera Overview

Viewfinder

While not strictly necessary, it's often useful to be able to see what the camera is pointing at. Most digital cameras allow an image feed from the camera sensor at a lower resolution (usually up to the size of the display of the camera) so you can compose a photo or video, and then switch to a slower but higher resolution mode for capturing the image.

Depending on whether you're using QML or C++, you can do this in multiple ways. In QML, you can use Camera and VideoOutput together to show a simple viewfinder:

 Camera {
     id: camera
     // You can adjust various settings in here
 }

 VideoOutput {
     source: camera
 }

In C++, your choice depends on whether you are using widgets, or QGraphicsView. The QVideoWidget class is used in the widgets case, and QGraphicsVideoItem is useful for QGraphicsView.

 camera = new QCamera;
 viewfinder = new QCameraViewfinder;
 camera->setViewfinder(viewfinder);
 viewfinder->show();

 camera->start(); // to start the viewfinder

For advanced usage (like processing viewfinder frames as they come, to detect objects or patterns), you can also derive from QAbstractVideoSurface and set that as the viewfinder for the QCamera object. In this case you will need to render the viewfinder image yourself.

 camera = new QCamera;
 mySurface = new MyVideoSurface;
 camera->setViewfinder(mySurface);

 camera->start();
 // MyVideoSurface::present(..) will be called with viewfinder frames

 imageCapture = new QCameraImageCapture(camera);

 camera->setCaptureMode(QCamera::CaptureStillImage);
 camera->start(); // Viewfinder frames start flowing

 //on half pressed shutter button
 camera->searchAndLock();

 //on shutter button pressed
 imageCapture->capture();

 //on shutter button released
 camera->unlock();

 camera = new QCamera;
 recorder = new QMediaRecorder(camera);

 camera->setCaptureMode(QCamera::CaptureVideo);
 camera->start();

 //on shutter button pressed
 recorder->record();

 // sometime later, or on another press
 recorder->stop();