Qt 5.7Qt MultimediaQML TypesCamera QML Type
Qt 5.7.1 Reference Documentation

Contents

Camera QML Type

Access viewfinder frames, and take photos and movies. More...

Import Statement: import QtMultimedia 5.7
Inherits:

QtObject

Properties

Signals

Methods

Detailed Description

You can use Camera to capture images and movies from a camera, and manipulate the capture and processing settings that get applied to the images. To display the viewfinder you can use VideoOutput with the Camera set as the source.


  Item {
      width: 640
      height: 360

      Camera {
          id: camera

          imageProcessing.whiteBalanceMode: CameraImageProcessing.WhiteBalanceFlash

          exposure {
              exposureCompensation: -1.0
              exposureMode: Camera.ExposurePortrait
          }

          flash.mode: Camera.FlashRedEyeReduction

          imageCapture {
              onImageCaptured: {
                  photoPreview.source = preview  // Show the preview in an Image
              }
          }
      }

      VideoOutput {
          source: camera
          anchors.fill: parent
          focus : visible // to receive focus and capture key events when visible
      }

      Image {
          id: photoPreview
      }
  }

If multiple cameras are available, you can select which one to use by setting the deviceId property to a value from QtMultimedia.availableCameras. On a mobile device, you can conveniently switch between front-facing and back-facing cameras by setting the position property.

The various settings and functionality of the Camera stack is spread across a few different child properties of Camera.

PropertyDescription
imageCaptureMethods and properties for capturing still images.
videoRecordingMethods and properties for capturing movies.
exposureMethods and properties for adjusting exposure (aperture, shutter speed etc).
focusMethods and properties for adjusting focus and providing feedback on autofocus progress.
flashMethods and properties for controlling the camera flash.
imageProcessingMethods and properties for adjusting camera image processing parameters.

Basic camera state management, error reporting, and simple zoom properties are available in the Camera itself. For integration with C++ code, the mediaObject property allows you to access the standard Qt Multimedia camera controls.

Many of the camera settings may take some time to apply, and might be limited to certain supported values depending on the hardware. Some camera settings may be set manually or automatically. These settings properties contain the current set value. For example, when autofocus is enabled the focus zones are exposed in the focus property.

For additional information, read also the camera overview.

Property Documentation

availability : enumeration

This property holds the availability state of the camera.

The availability states can be one of the following:

ValueDescription
AvailableThe camera is available to use
BusyThe camera is busy at the moment as it is being used by another process.
UnavailableThe camera is not available to use (there may be no camera hardware)
ResourceMissingThe camera cannot be used because of missing resources. It may be possible to try again at a later time.

cameraState : enumeration

This property holds the camera object's current state, which can be one of the following:

ValueDescription
UnloadedStateThe initial camera state, with the camera not loaded. The camera capabilities (with the exception of supported capture modes) are unknown. This state saves the most power, but takes the longest time to be ready for capture.

While the supported settings are unknown in this state, you can still set the camera capture settings like codec, resolution, or frame rate.

LoadedStateThe camera is loaded and ready to be configured.

In the Idle state you can query camera capabilities, set capture resolution, codecs, and so on.

The viewfinder is not active in the loaded state.

ActiveStateIn the active state the viewfinder frames are available and the camera is ready for capture.

The default camera state is ActiveState.


cameraStatus : enumeration

This property holds the camera object's current status, which can be one of the following:

ValueDescription
ActiveStatusThe camera has been started and can produce data, viewfinder displays video frames.

Depending on backend, changing camera settings such as capture mode, codecs, or resolution in ActiveState may lead to changing the status to LoadedStatus and StartingStatus while the settings are applied, and back to ActiveStatus when the camera is ready.

StartingStatusThe camera is starting as a result of state transition to Camera.ActiveState. The camera service is not ready to capture yet.
StoppingStatusThe camera is stopping as a result of state transition from Camera.ActiveState to Camera.LoadedState or Camera.UnloadedState.
StandbyStatusThe camera is in the power saving standby mode. The camera may enter standby mode after some time of inactivity in the Camera.LoadedState state.
LoadedStatusThe camera is loaded and ready to be configured. This status indicates the camera device is opened and it's possible to query for supported image and video capture settings such as resolution, frame rate, and codecs.
LoadingStatusThe camera device loading as a result of state transition from Camera.UnloadedState to Camera.LoadedState or Camera.ActiveState.
UnloadingStatusThe camera device is unloading as a result of state transition from Camera.LoadedState or Camera.ActiveState to Camera.UnloadedState.
UnloadedStatusThe initial camera status, with camera not loaded. The camera capabilities including supported capture settings may be unknown.
UnavailableStatusThe camera or camera backend is not available.

captureMode : enumeration

This property holds the camera capture mode, which can be one of the following:

ValueDescription
CaptureViewfinderCamera is only configured to display viewfinder.
CaptureStillImagePrepares the Camera for capturing still images.
CaptureVideoPrepares the Camera for capturing video.

The default capture mode is CaptureStillImage.


deviceId : string

This property holds the unique identifier for the camera device being used. It may not be human-readable.

You can get all available device IDs from QtMultimedia.availableCameras. If no value is provided or if set to an empty string, the system's default camera will be used.

If possible, cameraState, captureMode, digitalZoom and other camera parameters are preserved when changing the camera device.

This QML property was introduced in QtMultimedia 5.4.

See also displayName and position.


digitalZoom : real

This property holds the current digital zoom factor.


[read-only] displayName : string

This property holds the human-readable name of the camera.

You can use this property to display the name of the camera in a user interface.

This QML property was introduced in QtMultimedia 5.4.

See also deviceId.


errorCode : enumeration

This property holds the last error code.

See also error and errorString.


errorString : string

This property holds the last error string, if any.

See also error and errorCode.


lockStatus : enumeration

This property holds the status of all the requested camera locks.

The status can be one of the following values:

ValueDescription
UnlockedThe application is not interested in camera settings value. The camera may keep this parameter without changes, which is common with camera focus, or adjust exposure and white balance constantly to keep the viewfinder image nice.
SearchingThe application has requested the camera focus, exposure, or white balance lock with searchAndLock(). This state indicates the camera is focusing or calculating exposure and white balance.
LockedThe camera focus, exposure, or white balance is locked. The camera is ready to capture, and the application may check the exposure parameters.

The locked state usually means the requested parameter stays the same, except in cases where the parameter is requested to be updated constantly. For example in continuous focusing mode, the focus is considered locked as long as the object is in focus, even while the actual focusing distance may be constantly changing.


maximumDigitalZoom : real

This property holds the maximum digital zoom factor supported, or 1.0 if digital zoom is not supported.


maximumOpticalZoom : real

This property holds the maximum optical zoom factor supported, or 1.0 if optical zoom is not supported.


mediaObject : variant

This property holds the native media object for the camera.

It can be used to get a pointer to a QCamera object in order to integrate with C++ code.


  QObject *qmlCamera; // The QML Camera object
  QCamera *camera = qvariant_cast<QCamera *>(qmlCamera->property("mediaObject"));

Note: This property is not accessible from QML.


metaData group

metaData.cameraManufacturer : variant

metaData.cameraModel : variant

metaData.event : variant

metaData.subject : variant

metaData.orientation : variant

metaData.dateTimeOriginal : variant

metaData.gpsLatitude : variant

metaData.gpsLongitude : variant

metaData.gpsAltitude : variant

metaData.gpsTimestamp : variant

metaData.gpsTrack : variant

metaData.gpsSpeed : variant

metaData.gpsImgDirection : variant

metaData.gpsProcessingMethod : variant

These properties hold the meta data for the camera captures.

  • metaData.cameraManufacturer holds the name of the manufacturer of the camera.
  • metaData.cameraModel holds the name of the model of the camera.
  • metaData.event holds the event during which the photo or video is to be captured.
  • metaData.subject holds the name of the subject of the capture or recording.
  • metaData.orientation holds the clockwise rotation of the camera at time of capture.
  • metaData.dateTimeOriginal holds the initial time at which the photo or video is captured.
  • metaData.gpsLatitude holds the latitude of the camera in decimal degrees at time of capture.
  • metaData.gpsLongitude holds the longitude of the camera in decimal degrees at time of capture.
  • metaData.gpsAltitude holds the altitude of the camera in meters at time of capture.
  • metaData.gpsTimestamp holds the timestamp of the GPS position data.
  • metaData.gpsTrack holds direction of movement of the camera at the time of capture. It is measured in degrees clockwise from north.
  • metaData.gpsSpeed holds the velocity in kilometers per hour of the camera at time of capture.
  • metaData.gpsImgDirection holds direction the camera is facing at the time of capture. It is measured in degrees clockwise from north.
  • metaData.gpsProcessingMethod holds the name of the method for determining the GPS position.

This property group was introduced in Qt 5.4.

See also QMediaMetaData.


opticalZoom : real

This property holds the current optical zoom factor.


[read-only] orientation : int

This property holds the physical orientation of the camera sensor.

The value is the orientation angle (clockwise, in steps of 90 degrees) of the camera sensor in relation to the display in its natural orientation.

For example, suppose a mobile device which is naturally in portrait orientation. The back-facing camera is mounted in landscape. If the top side of the camera sensor is aligned with the right edge of the screen in natural orientation, orientation returns 270. If the top side of a front-facing camera sensor is aligned with the right edge of the screen, orientation returns 90.

This QML property was introduced in QtMultimedia 5.4.

See also VideoOutput::orientation.


position : enumeration

This property holds the physical position of the camera on the hardware system.

The position can be one of the following:

  • Camera.UnspecifiedPosition - the camera position is unspecified or unknown.
  • Camera.BackFace - the camera is on the back face of the system hardware. For example on a mobile device, it means it is on the opposite side to that of the screem.
  • Camera.FrontFace - the camera is on the front face of the system hardware. For example on a mobile device, it means it is on the same side as that of the screen. Viewfinder frames of front-facing cameras are mirrored horizontally, so the users can see themselves as looking into a mirror. Captured images or videos are not mirrored.

On a mobile device it can be used to easily choose between front-facing and back-facing cameras. If this property is set to Camera.UnspecifiedPosition, the system's default camera will be used.

If possible, cameraState, captureMode, digitalZoom and other camera parameters are preserved when changing the camera device.

This QML property was introduced in QtMultimedia 5.4.

See also deviceId.


viewfinder group

viewfinder.resolution : size

viewfinder.minimumFrameRate : real

viewfinder.maximumFrameRate : real

These properties hold the viewfinder settings.

viewfinder.resolution holds the resolution of the camera viewfinder. If no resolution is given or if it is empty, the backend uses a default value.

viewfinder.minimumFrameRate holds the minimum frame rate for the viewfinder in frames per second. If no value is given or if set to 0, the backend uses a default value.

viewfinder.maximumFrameRate holds the maximum frame rate for the viewfinder in frames per second. If no value is given or if set to 0, the backend uses a default value.

If viewfinder.minimumFrameRate is equal to viewfinder.maximumFrameRate, the frame rate is fixed. If not, the actual frame rate fluctuates between the two values.

Changing the viewfinder settings while the camera is in the Camera.ActiveState state may cause the camera to be restarted.

If the camera is used to capture videos or images, the viewfinder settings might be ignored if they conflict with the capture settings. You can check the actual viewfinder settings once the camera is in the Camera.ActiveStatus status.

Supported values can be retrieved with supportedViewfinderResolutions() and supportedViewfinderFrameRateRanges().

This property group was introduced in Qt 5.4.


Signal Documentation

cameraStateChanged(state)

This signal is emitted when the camera state has changed to state. Since the state changes may take some time to occur this signal may arrive sometime after the state change has been requested.

The corresponding handler is onCameraStateChanged.


digitalZoomChanged(zoom)

This signal is emitted when the digital zoom setting has changed to zoom.

The corresponding handler is onDigitalZoomChanged.


error(errorCode, errorString)

This signal is emitted when an error occurs. The enumeration value errorCode is one of the values defined below, and a descriptive string value is available in errorString.

ValueDescription
NoErrorNo errors have occurred.
CameraErrorAn error has occurred.
InvalidRequestErrorSystem resource doesn't support requested functionality.
ServiceMissingErrorNo camera service available.
NotSupportedFeatureErrorThe feature is not supported.

The corresponding handler is onError.

See also errorCode and errorString.


lockStatusChanged()

This signal is emitted when the lock status (focus, exposure etc) changes. This can happen when locking (e.g. autofocusing) is complete or has failed.

The corresponding handler is onLockStatusChanged.


manualWhiteBalanceChanged(qreal)

This signal is emitted when the manualWhiteBalance property is changed.

The corresponding handler is onManualWhiteBalanceChanged.


maximumDigitalZoomChanged(zoom)

This signal is emitted when the maximum digital zoom setting has changed to zoom. This can occur when you change between video and still image capture modes, or the capture settings are changed.

The corresponding handler is onMaximumDigitalZoomChanged.


maximumOpticalZoomChanged(zoom)

This signal is emitted when the maximum optical zoom setting has changed to zoom. This can occur when you change between video and still image capture modes, or the capture settings are changed.

The corresponding handler is onMaximumOpticalZoomChanged.


opticalZoomChanged(zoom)

This signal is emitted when the optical zoom setting has changed to zoom.

The corresponding handler is onOpticalZoomChanged.


whiteBalanceModeChanged(Camera::WhiteBalanceMode)

This signal is emitted when the whiteBalanceMode property is changed.

The corresponding handler is onWhiteBalanceModeChanged.


Method Documentation

searchAndLock()

Start focusing, exposure and white balance calculation.

This is appropriate to call when the camera focus button is pressed (or on a camera capture button half-press). If the camera supports autofocusing, information on the focus zones is available through the focus property.


start()

Starts the camera. Viewfinder frames will be available and image or movie capture will be possible.


stop()

Stops the camera, but leaves the camera stack loaded.


list<object> supportedViewfinderFrameRateRanges(size resolution = undefined)

Returns a list of supported viewfinder frame rate ranges.

Each range object in the list has the minimumFrameRate and maximumFrameRate properties.

If the optional parameter resolution is specified, the returned list is reduced to frame rate ranges supported for the given resolution.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This QML method was introduced in Qt 5.5.

See also viewfinder.


list<size> supportedViewfinderResolutions(real minimumFrameRate = undefined, real maximumFrameRate = undefined)

Returns a list of supported viewfinder resolutions.

If both optional parameters minimumFrameRate and maximumFrameRate are specified, the returned list is reduced to resolutions supported for the given frame rate range.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This QML method was introduced in Qt 5.5.

See also viewfinder.


unlock()

Unlock focus, exposure and white balance locks.


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