Camera

The Camera API provides control of system camera devices. Providing support for still or video image capture with sound support.

Namespace

The QtMobility APIs are placed into the QtMobility namespace. This is done to facilitate the future migration of QtMobility APIs into Qt. See the Quickstart guide for an example on how the namespace impacts on application development.

Overview

The Camera API allows high level control of various aspects of still images and video. Camera is a part of the Multimedia API and this relationship is apparent when you notice that certain core classes are subclassed from some Multimedia base classes including QMediaObject and QMediaControl.

Still Images

In order to capture an image we need to create a QCamera object and use it to initialize a QVideoWidget, so we can see where the camera is pointing - a viewfinder. The camera object is also used to initialize a new QCameraImageCapture object, imageCapture. All that is then needed is to start the camera, lock it so that the settings are not changed while the image capture occurs, capture the image, and finally unlock the camera ready for the next photo.

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

 imageCapture = new QCameraImageCapture(camera);

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

 //on half pressed shutter button
 camera->searchA{QCameraFocus::FocusMode}{ndLock();

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

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

Alternatively, we could have used a QGraphicsVideoItem as a viewfinder.

Video Clips

Previously we saw code that allowed the capture of a still image. Recording video requires the use of a QMediaRecorder object and a QAudioCaptureSource for sound.

To record video we need to create a camera object as before but this time as well as creating a viewfinder, we will also initialize a media recorder object.

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

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

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

Signals from the mediaRecorder can be connected to slots to react to changes in the state of the recorder or error events. Recording itself starts with the record() function of mediaRecorder being called, this causes the signal stateChanged() to be emitted. The recording process can be changed with the record(), pause(), stop() and setMuted() slots in QMediaRecorder.

When the camera is in video mode, as decided by the application, then as the shutter button is pressed the camera is locked as before but instead the record() function in QMediaRecorder is used.

Focus

Focusing is managed by the classes QCameraFocus and QCameraFocusControl. QCameraFocus allows the developer to set the general policy by means of the enums for the FocusMode and the FocusPointMode. FocusMode deals with settings such as AutoFocus, ContinuousFocus and InfinityFocus, whereas FocusPointMode deals with the various focus zones within the view. FocusPointMode has support for face recognition, center focus and a custom focus where the focus point can be specified.

Cancelling Asynchronous Operations

Various operations such as image capture and auto focusing occur asynchrously. These operations can often be cancelled by the start of a new operation as long as this is supported by the backend. For image capture, the operation can be cancelled by calling cancelCapture(). For AutoFocus, autoexposure or white balance cancellation can be done by calling QCamera::unlock(QCamera::LockFocus).

Camera Controls

Control Name	Description
camera	the interface for system camera devices
exposure	Includes: flash mode; flash power; metering mode; aperture; shutter speed, iso setting
focus	Includes: optical zoom; digital zoom; focus point; focus zones
image processing	white balance; contrast; saturation; sharpen; denoise
locks	handles the locking and unlocking of camera devices

Classes

QCamera	Interface for system camera devices
QCameraExposure	Interface for exposure related camera settings
QCameraFocus	Interface for focus and zoom related camera settings
QCameraImageCapture	Used for the recording of media content
QCameraImageProcessing	Interface for focus and zoom related camera settings
QCameraViewfinder	Camera viewfinder widget