QCameraFocus Class

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()
      }
  }