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HighGUI
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.. highlight:: cpp

Using Kinect sensor
===================

Kinect sensor is supported through ``VideoCapture`` class. Depth map, RGB image and some other formats of Kinect output can be retrieved by using familiar interface of ``VideoCapture``.

In order to use Kinect with OpenCV you should do the following preliminary steps:

#.
    Install OpenNI library (from here \url{http://www.openni.org/downloadfiles}) and PrimeSensor Module for OpenNI (from here https://github.com/avin2/SensorKinect}). The installation should be done to default folders listed in the instructions of these products:

    .. code-block:: text
    
        OpenNI:
            Linux & MacOSX:
                Libs into: /usr/lib
                Includes into: /usr/include/ni
            Windows:
                Libs into: c:/Program Files/OpenNI/Lib
                Includes into: c:/Program Files/OpenNI/Include
        PrimeSensor Module:
            Linux & MacOSX:
                Bins into: /usr/bin
            Windows:
                Bins into: c:/Program Files/Prime Sense/Sensor/Bin

    If one or both products were installed to the other folders, the user should change corresponding CMake variables ``OPENNI_LIB_DIR``, ``OPENNI_INCLUDE_DIR`` or/and ``OPENNI_PRIME_SENSOR_MODULE_BIN_DIR``.
    
#.
    Configure OpenCV with OpenNI support by setting \texttt{WITH\_OPENNI} flag in CMake. If OpenNI is found in default install folders OpenCV will be built with OpenNI library regardless of whether PrimeSensor Module is found or not. If PrimeSensor Module was not found you will get a warning in CMake log. Without PrimeSensor module OpenCV will be successfully compiled with OpenNI library, but ``VideoCapture`` object will not grab data from Kinect sensor.

#.
    Build OpenCV.

VideoCapture can retrieve the following Kinect data:

#.
    data given from depth generator:
      * ``OPENNI_DEPTH_MAP``          - depth values in mm (CV_16UC1)
      * ``OPENNI_POINT_CLOUD_MAP``    - XYZ in meters (CV_32FC3)
      * ``OPENNI_DISPARITY_MAP``      - disparity in pixels (CV_8UC1)
      * ``OPENNI_DISPARITY_MAP_32F``  - disparity in pixels (CV_32FC1)
      * ``OPENNI_VALID_DEPTH_MASK``   - mask of valid pixels (not ocluded, not shaded etc.) (CV_8UC1)
#.
    data given from RGB image generator:
      * ``OPENNI_BGR_IMAGE``          - color image (CV_8UC3)
      * ``OPENNI_GRAY_IMAGE``         - gray image (CV_8UC1)

In order to get depth map from Kinect use ``VideoCapture::operator >>``, e. g. ::

    VideoCapture capture( CV_CAP_OPENNI );
    for(;;)
    {
        Mat depthMap;    
        capture >> depthMap;
    
        if( waitKey( 30 ) >= 0 )
            break;
    }

For getting several Kinect maps use ``VideoCapture::grab`` and ``VideoCapture::retrieve``, e.g. ::

    VideoCapture capture(0); // or CV_CAP_OPENNI
    for(;;)
    {
        Mat depthMap;
        Mat rgbImage
    
        capture.grab();
    
        capture.retrieve( depthMap, OPENNI_DEPTH_MAP );
        capture.retrieve( bgrImage, OPENNI_BGR_IMAGE );
    
        if( waitKey( 30 ) >= 0 )
            break;
    }

For setting and getting some property of Kinect data generators use ``VideoCapture::set`` and ``VideoCapture::get`` methods respectively, e.g. ::

    VideoCapture capture( CV_CAP_OPENNI );    
    capture.set( CV_CAP_OPENNI_IMAGE_GENERATOR_OUTPUT_MODE, CV_CAP_OPENNI_VGA_30HZ );
    cout << "FPS    " << capture.get( CV_CAP_OPENNI_IMAGE_GENERATOR+CV_CAP_PROP_FPS ) << endl;

Since two types of Kinect's data generators are supported (image generator and depth generator), there are two flags that should be used to set/get property of the needed generator:

* CV_CAP_OPENNI_IMAGE_GENERATOR -- A flag for access to the image generator properties.

* CV_CAP_OPENNI_DEPTH_GENERATOR -- A flag for access to the depth generator properties. This flag value is assumed by default if neither of the two possible values of the property is not set.

Flags specifing the needed generator type must be used in combination with particular generator property. The following properties of cameras available through OpenNI interfaces are supported:

* 
  For image generator:
  
  - ``CV_CAP_PROP_OPENNI_OUTPUT_MODE`` -- Two output modes are supported: ``CV_CAP_OPENNI_VGA_30HZ`` used by default (image generator returns images in VGA resolution with 30 FPS) or ``CV_CAP_OPENNI_SXGA_15HZ`` (image generator returns images in SXGA resolution with 15 FPS); depth generator's maps are always in VGA resolution.
  

* 
  For depth generator:

  - ``CV_CAP_PROP_OPENNI_REGISTRATION`` -- Flag that synchronizes the remapping depth map to image map  by changing depth generator's view point (if the flag is ``"on"``) or sets this view point to its normal one (if the flag is ``"off"``).
  
    Next properties are available for getting only:
  
  - ``CV_CAP_PROP_OPENNI_FRAME_MAX_DEPTH`` -- A maximum supported depth of Kinect in mm.
  - ``CV_CAP_PROP_OPENNI_BASELINE`` -- Baseline value in mm. 
  - ``CV_CAP_PROP_OPENNI_FOCAL_LENGTH`` -- A focal length in pixels. 
  - ``CV_CAP_PROP_FRAME_WIDTH`` -- Frame width in pixels.
  - ``CV_CAP_PROP_FRAME_HEIGHT`` -- Frame height in pixels.
  - ``CV_CAP_PROP_FPS`` -- Frame rate in FPS.

*
  Some typical flags combinations "generator type + property" are defined as single flags:
  
    - ``CV_CAP_OPENNI_IMAGE_GENERATOR_OUTPUT_MODE = CV_CAP_OPENNI_IMAGE_GENERATOR + CV_CAP_PROP_OPENNI_OUTPUT_MODE``
    - ``CV_CAP_OPENNI_DEPTH_GENERATOR_BASELINE = CV_CAP_OPENNI_DEPTH_GENERATOR + CV_CAP_PROP_OPENNI_BASELINE``
    - ``CV_CAP_OPENNI_DEPTH_GENERATOR_FOCAL_LENGTH = CV_CAP_OPENNI_DEPTH_GENERATOR + CV_CAP_PROP_OPENNI_FOCAL_LENGTH``
    - ``CV_CAP_OPENNI_DEPTH_GENERATOR_REGISTRATION_ON = CV_CAP_OPENNI_DEPTH_GENERATOR + CV_CAP_PROP_OPENNI_REGISTRATION_ON``
    
For more information please refer to a Kinect example of usage ``kinect_maps.cpp`` in ``opencv/samples/cpp`` folder.
