Qt 5.9 | Qt Multimedia | C++ Classes | QCameraFocus

Qt 5.9.4 Reference Documentation

# QCameraFocus Class

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

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

- 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
FocusModes | focusMode() const
FocusPointMode | focusPointMode() const
QCameraFocusZoneList | focusZones() const
bool | isAvailable() const
bool | isFocusModeSupported(FocusModes mode) const
bool | isFocusPointModeSupported(FocusPointMode mode) const
qreal | maximumDigitalZoom() const
qreal | maximumOpticalZoom() const
qreal | opticalZoom() const
void | setCustomFocusPoint(const QPointF &point)
void | setFocusMode(FocusModes mode)
void | setFocusPointMode(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)

## Detailed Description

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

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);
      QList<QCameraFocusZone> zones = focus->focusZones();
      foreach (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::FocusMode
flags 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.

## Property Documentation

### customFocusPoint : QPointF

This property represents the position of the custom focus point, in relative frame coordinates: QPointF(0,0) points to the left top frame point, QPointF(0.5,0.5) points to the frame center.

The custom focus point property is used only in `FocusPointCustom` focus mode.

Access functions:

QPointF | customFocusPoint() const
void | setCustomFocusPoint(const QPointF &point)

### digitalZoom : const qreal

This property holds the current digital zoom value.

Access functions:

qreal | digitalZoom() const

Notifier signal:

void | digitalZoomChanged(qreal value)

See also QCameraFocus::opticalZoom.

### focusMode : FocusModes

This property holds the current camera focus mode.

This controls the way the camera lens assembly is configured.

Access functions:

FocusModes | focusMode() const
void | setFocusMode(FocusModes mode)

See also QCameraFocus::isFocusModeSupported().

### focusPointMode : FocusPointMode

This property holds the current camera focus point selection mode.

If the camera focus mode is set to use an autofocusing mode, this property controls the way the camera will select areas of the frame to use for autofocusing.

Access functions:

FocusPointMode | focusPointMode() const
void | setFocusPointMode(FocusPointMode mode)

See also QCameraFocus::isFocusPointModeSupported().

### focusZones : const QCameraFocusZoneList

Returns the list of active focus zones.

If QCamera::FocusPointAuto or QCamera::FocusPointFaceDetection focus mode is selected this method returns the list of zones the camera is actually focused on.

The coordinates system is the same as for custom focus points: QPointF(0,0) points to the left top frame point, QPointF(0.5,0.5) points to the frame center.

Access functions:

QCameraFocusZoneList | focusZones() const

Notifier signal:

void | focusZonesChanged()

### opticalZoom : const qreal

This property holds the current optical zoom value.

Access functions:

qreal | opticalZoom() const

Notifier signal:

void | opticalZoomChanged(qreal value)

See also QCameraFocus::digitalZoom.

## 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.

### 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(FocusModes mode) const

Returns true if the focus mode is supported by camera.

### bool QCameraFocus::isFocusPointModeSupported(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.

### `[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.

### qreal QCameraFocus::maximumOpticalZoom() const

Returns the maximum optical zoom.

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

### `[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.

### 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.