QCameraFocus Class

The QCameraFocus class provides an interface for focus and zoom related camera settings. More...

Header:	#include <QCameraFocus>
qmake:	QT += multimedia
Inherits:	QObject

• List of all members, including inherited members

Public Types

enum	FocusMode { ManualFocus, HyperfocalFocus, InfinityFocus, AutoFocus, ContinuousFocus, MacroFocus }
flags	FocusModes
enum	FocusPointMode { FocusPointAuto, FocusPointCenter, FocusPointFaceDetection, FocusPointCustom }

Properties

customFocusPoint : QPointF digitalZoom : const qreal focusMode : FocusModes

focusPointMode : FocusPointMode focusZones : const QCameraFocusZoneList opticalZoom : const qreal

Public Functions

QPointF	customFocusPoint() const
qreal	digitalZoom() const
QCameraFocus::FocusModes	focusMode() const
QCameraFocus::FocusPointMode	focusPointMode() const
QCameraFocusZoneList	focusZones() const
bool	isAvailable() const
bool	isFocusModeSupported(QCameraFocus::FocusModes mode) const
bool	isFocusPointModeSupported(QCameraFocus::FocusPointMode mode) const
qreal	maximumDigitalZoom() const
qreal	maximumOpticalZoom() const
qreal	opticalZoom() const
void	setCustomFocusPoint(const QPointF &point)
void	setFocusMode(QCameraFocus::FocusModes mode)
void	setFocusPointMode(QCameraFocus::FocusPointMode mode)
void	zoomTo(qreal optical, qreal digital)

Signals

void	digitalZoomChanged(qreal value)
void	focusZonesChanged()
void	maximumDigitalZoomChanged(qreal zoom)
void	maximumOpticalZoomChanged(qreal zoom)
void	opticalZoomChanged(qreal value)

Protected Functions

virtual

~QCameraFocus()

Detailed Description

On hardware that supports it, this class lets you adjust the focus or zoom (both optical and digital). This also includes things like "Macro" mode for close up work (e.g. reading barcodes, or recognising letters), or "touch to focus" - indicating an interesting area of the viewfinder for the hardware to attempt to focus on.

QCameraFocus *focus = camera->focus();
focus->setFocusPointMode(QCameraFocus::FocusPointCustom);
focus->setCustomFocusPoint(QPointF(0.25f, 0.75f)); // A point near the bottom left, 25% away from the corner, near that shiny vase

Zooming can be accomplished in a number of ways - usually the more expensive but higher quality approach is an optical zoom, which allows using the full extent of the camera sensor to gather image pixels. In addition it is possible to digitally zoom, which will generally just enlarge part of the sensor frame and throw away other parts. If the camera hardware supports optical zoom this should generally always be used first. The maximumOpticalZoom() method allows this to be checked. The zoomTo() method allows changing both optical and digital zoom at once.

focus->zoomTo(3.0, 4.0); // Super zoom!

Some notes on autofocus

Some hardware supports a movable focus lens assembly, and typically this hardware also supports automatically focusing via some heuristic. You can influence this via the FocusPointMode setting - typically the center of the frame is brought into focus, but some hardware also supports focusing on any faces detected in the frame, or on a specific point (usually provided by a user in a "touch to focus" scenario).

This class (in combination with QCameraFocusZone) can expose information on what parts of the camera sensor image are in focus or are being used for autofocusing via the focusZones() property:

focus->setFocusPointMode(QCameraFocus::FocusPointAuto);
const QList<QCameraFocusZone> zones = focus->focusZones();
for (const QCameraFocusZone &zone : zones) {
    if (zone.status() == QCameraFocusZone::Focused) {
        // Draw a green box at zone.area()
    } else if (zone.status() == QCameraFocusZone::Selected) {
        // This area is selected for autofocusing, but is not in focus
        // Draw a yellow box at zone.area()
    }
}

See also QCameraFocusZone.

Member Type Documentation

enum QCameraFocus::FocusModeflags QCameraFocus::FocusModes

Constant	Value	Description
QCameraFocus::ManualFocus	0x1	Manual or fixed focus mode.
QCameraFocus::HyperfocalFocus	0x02	Focus to hyperfocal distance, with the maximum depth of field achieved. All objects at distances from half of this distance out to infinity will be acceptably sharp.
QCameraFocus::InfinityFocus	0x04	Focus strictly to infinity.
QCameraFocus::AutoFocus	0x8	One-shot auto focus mode.
QCameraFocus::ContinuousFocus	0x10	Continuous auto focus mode.
QCameraFocus::MacroFocus	0x20	One shot auto focus to objects close to camera.

The FocusModes type is a typedef for QFlags<FocusMode>. It stores an OR combination of FocusMode values.

enum QCameraFocus::FocusPointMode

Constant	Value	Description
QCameraFocus::FocusPointAuto	0	Automatically select one or multiple focus points.
QCameraFocus::FocusPointCenter	1	Focus to the frame center.
QCameraFocus::FocusPointFaceDetection	2	Focus on faces in the frame.
QCameraFocus::FocusPointCustom	3	Focus to the custom point, defined by QCameraFocus::customFocusPoint property.

Member Function Documentation

[signal] void QCameraFocus::digitalZoomChanged(qreal value)

Signal emitted when digital zoom value changes to new value.

Note: Notifier signal for property digitalZoom.

[signal] void QCameraFocus::focusZonesChanged()

This signal is emitted when the set of zones used in autofocusing is changed.

This can change when a zone is focused or loses focus, or new focus zones have been detected.

Note: Notifier signal for property focusZones.

[signal] void QCameraFocus::maximumDigitalZoomChanged(qreal zoom)

Signal emitted when the maximum supported digital zoom value changed.

The maximum supported zoom value can depend on other camera settings, like capture mode or resolution.

[signal] void QCameraFocus::maximumOpticalZoomChanged(qreal zoom)

Signal emitted when the maximum supported optical zoom value changed.

[signal] void QCameraFocus::opticalZoomChanged(qreal value)

Signal emitted when optical zoom value changes to new value.

Note: Notifier signal for property opticalZoom.

[virtual protected] QCameraFocus::~QCameraFocus()

Destroys the camera focus object.

bool QCameraFocus::isAvailable() const

Returns true if focus related settings are supported by this camera.

You may need to also check if any specific features are supported.

bool QCameraFocus::isFocusModeSupported(QCameraFocus::FocusModes mode) const

Returns true if the focus mode is supported by camera.

bool QCameraFocus::isFocusPointModeSupported(QCameraFocus::FocusPointMode mode) const

Returns true if focus point mode is supported.

qreal QCameraFocus::maximumDigitalZoom() const

Returns the maximum digital zoom

This will be 1.0 on cameras that do not support digital zoom.

qreal QCameraFocus::maximumOpticalZoom() const

Returns the maximum optical zoom.

This will be 1.0 on cameras that do not support optical zoom.

void QCameraFocus::zoomTo(qreal optical, qreal digital)

Set the camera optical and digital zoom values.

Since there may be a physical component to move, the change in zoom value may not be instantaneous.