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# Camera Calibration and 3D Reconstruction

## ocl::StereoBM_OCL

class `ocl::``StereoBM_OCL`

Class computing stereo correspondence (disparity map) using the block matching algorithm.

    class CV_EXPORTS StereoBM_OCL
    {
    public:
        enum { BASIC_PRESET = 0, PREFILTER_XSOBEL = 1 };

        enum { DEFAULT_NDISP = 64, DEFAULT_WINSZ = 19 };

        //! the default constructor
        StereoBM_OCL();
        //! the full constructor taking the camera-specific preset, number of disparities and the SAD window size. ndisparities must be multiple of 8.
        StereoBM_OCL(int preset, int ndisparities = DEFAULT_NDISP, int winSize = DEFAULT_WINSZ);

        //! the stereo correspondence operator. Finds the disparity for the specified rectified stereo pair
        //! Output disparity has CV_8U type.
        void operator() ( const oclMat &left, const oclMat &right, oclMat &disparity);

        //! Some heuristics that tries to estmate
        // if current GPU will be faster then CPU in this algorithm.
        // It queries current active device.
        static bool checkIfGpuCallReasonable();

        int preset;
        int ndisp;
        int winSize;

        // If avergeTexThreshold  == 0 => post procesing is disabled
        // If avergeTexThreshold != 0 then disparity is set 0 in each point (x,y) where for left image
        // SumOfHorizontalGradiensInWindow(x, y, winSize) < (winSize * winSize) * avergeTexThreshold
        // i.e. input left image is low textured.
        float avergeTexThreshold;
    private:
        /* hidden */
    };

The class also performs pre- and post-filtering steps: Sobel pre-filtering (if `PREFILTER_XSOBEL` flag is set) and low textureness filtering (if `averageTexThreshols > 0` ). If `avergeTexThreshold = 0` , low textureness filtering is disabled. Otherwise, the disparity is set to 0 in each point `(x, y)` , where for the left image

\sum HorizontalGradiensInWindow(x, y, winSize) < (winSize \cdot winSize) \cdot avergeTexThreshold

This means that the input left image is low textured.

## ocl::StereoBM_OCL::StereoBM_OCL

Enables `ocl::StereoBM_OCL` constructors.

C++:`` `ocl::StereoBM_OCL::``StereoBM_OCL`()

C++:`` `ocl::StereoBM_OCL::``StereoBM_OCL`(int preset, int ndisparities=DEFAULT_NDISP, int winSize=DEFAULT_WINSZ)

  Parameters: | preset – Parameter presetting: BASIC_PRESET Basic mode without pre-processing. PREFILTER_XSOBEL Sobel pre-filtering mode. ndisparities – Number of disparities. It must be a multiple of 8 and less or equal to 256. winSize – Block size.

## ocl::StereoBM_OCL::operator ()

Enables the stereo correspondence operator that finds the disparity for the specified rectified stereo pair.

C++:`` void `ocl::StereoBM_OCL::``operator()`(const oclMat& left, const oclMat& right, oclMat& disparity)

  Parameters: | left – Left image. Only `CV_8UC1` type is supported. right – Right image with the same size and the same type as the left one. disparity – Output disparity map. It is a `CV_8UC1` image with the same size as the input images.

## ocl::StereoBM_OCL::checkIfGpuCallReasonable

Uses a heuristic method to estimate whether the current GPU is faster than the CPU in this algorithm. It queries the currently active device.

C++:`` bool `ocl::StereoBM_OCL::``checkIfGpuCallReasonable`()

## ocl::StereoBeliefPropagation

class `ocl::``StereoBeliefPropagation`

Class computing stereo correspondence using the belief propagation algorithm.

    class CV_EXPORTS StereoBeliefPropagation
    {
    public:
        enum { DEFAULT_NDISP  = 64 };
        enum { DEFAULT_ITERS  = 5  };
        enum { DEFAULT_LEVELS = 5  };
        static void estimateRecommendedParams(int width, int height, int &ndisp, int &iters, int &levels);
        explicit StereoBeliefPropagation(int ndisp  = DEFAULT_NDISP,
                                         int iters  = DEFAULT_ITERS,
                                         int levels = DEFAULT_LEVELS,
                                         int msg_type = CV_16S);
        StereoBeliefPropagation(int ndisp, int iters, int levels,
                                float max_data_term, float data_weight,
                                float max_disc_term, float disc_single_jump,
                                int msg_type = CV_32F);
        void operator()(const oclMat &left, const oclMat &right, oclMat &disparity);
        void operator()(const oclMat &data, oclMat &disparity);
        int ndisp;
        int iters;
        int levels;
        float max_data_term;
        float data_weight;
        float max_disc_term;
        float disc_single_jump;
        int msg_type;
    private:
        /* hidden */
    };

The class implements algorithm described in [Felzenszwalb2006] . It can compute own data cost (using a truncated linear model) or use a user-provided data cost.

Note

`StereoBeliefPropagation` requires a lot of memory for message storage:

width \_ step \cdot height \cdot ndisp \cdot 4 \cdot (1 + 0.25)

and for data cost storage:

width\_step \cdot height \cdot ndisp \cdot (1 + 0.25 + 0.0625 + \dotsm + \frac{1}{4^{levels}})

`width_step` is the number of bytes in a line including padding.

## ocl::StereoBeliefPropagation::StereoBeliefPropagation

Enables the `ocl::StereoBeliefPropagation` constructors.

C++:`` `ocl::StereoBeliefPropagation::``StereoBeliefPropagation`(int ndisp=DEFAULT_NDISP, int iters=DEFAULT_ITERS, int levels=DEFAULT_LEVELS, int msg_type=CV_16S)

C++:`` `ocl::StereoBeliefPropagation::``StereoBeliefPropagation`(int ndisp, int iters, int levels, float max_data_term, float data_weight, float max_disc_term, float disc_single_jump, int msg_type=CV_32F)

  Parameters: | ndisp – Number of disparities. iters – Number of BP iterations on each level. levels – Number of levels. max_data_term – Threshold for data cost truncation. data_weight – Data weight. max_disc_term – Threshold for discontinuity truncation. disc_single_jump – Discontinuity single jump. msg_type – Type for messages. `CV_16SC1` and `CV_32FC1` types are supported.

`StereoBeliefPropagation` uses a truncated linear model for the data cost and discontinuity terms:

DataCost = data \_ weight \cdot \min ( \lvert Img_Left(x,y)-Img_Right(x-d,y) \rvert , max \_ data \_ term)

DiscTerm = \min (disc \_ single \_ jump \cdot \lvert f_1-f_2 \rvert , max \_ disc \_ term)

For more details, see [Felzenszwalb2006].

By default, `ocl::StereoBeliefPropagation` uses floating-point arithmetics and the `CV_32FC1` type for messages. But it can also use fixed-point arithmetics and the `CV_16SC1` message type for better performance. To avoid an overflow in this case, the parameters must satisfy the following requirement:

10 \cdot 2^{levels-1} \cdot max \_ data \_ term < SHRT \_ MAX

## ocl::StereoBeliefPropagation::estimateRecommendedParams

Uses a heuristic method to compute the recommended parameters ( `ndisp`, `iters` and `levels` ) for the specified image size ( `width` and `height` ).

C++:`` void `ocl::StereoBeliefPropagation::``estimateRecommendedParams`(int width, int height, int& ndisp, int& iters, int& levels)

## ocl::StereoBeliefPropagation::operator ()

Enables the stereo correspondence operator that finds the disparity for the specified rectified stereo pair or data cost.

C++:`` void `ocl::StereoBeliefPropagation::``operator()`(const oclMat& left, const oclMat& right, oclMat& disparity)

C++:`` void `ocl::StereoBeliefPropagation::``operator()`(const oclMat& data, oclMat& disparity)

  Parameters: | left – Left image. `CV_8UC1` , `CV_8UC3` and `CV_8UC4` types are supported. right – Right image with the same size and the same type as the left one. data – User-specified data cost, a matrix of `msg_type` type and `Size(<image columns>*ndisp, <image rows>)` size. disparity – Output disparity map. If `disparity` is empty, the output type is `CV_16SC1` . Otherwise, the type is retained.

## ocl::StereoConstantSpaceBP

class `ocl::``StereoConstantSpaceBP`

Class computing stereo correspondence using the constant space belief propagation algorithm.

    class CV_EXPORTS StereoConstantSpaceBP
    {
    public:
        enum { DEFAULT_NDISP    = 128 };
        enum { DEFAULT_ITERS    = 8   };
        enum { DEFAULT_LEVELS   = 4   };
        enum { DEFAULT_NR_PLANE = 4   };
        static void estimateRecommendedParams(int width, int height, int &ndisp, int &iters, int &levels, int &nr_plane);
        explicit StereoConstantSpaceBP(
            int ndisp    = DEFAULT_NDISP,
            int iters    = DEFAULT_ITERS,
            int levels   = DEFAULT_LEVELS,
            int nr_plane = DEFAULT_NR_PLANE,
            int msg_type = CV_32F);
        StereoConstantSpaceBP(int ndisp, int iters, int levels, int nr_plane,
            float max_data_term, float data_weight, float max_disc_term, float disc_single_jump,
            int min_disp_th = 0,
            int msg_type = CV_32F);
        void operator()(const oclMat &left, const oclMat &right, oclMat &disparity);
        int ndisp;
        int iters;
        int levels;
        int nr_plane;
        float max_data_term;
        float data_weight;
        float max_disc_term;
        float disc_single_jump;
        int min_disp_th;
        int msg_type;
        bool use_local_init_data_cost;
    private:
        /* hidden */
    };

The class implements algorithm described in [Yang2010]. `StereoConstantSpaceBP` supports both local minimum and global minimum data cost initialization algorithms. For more details, see the paper mentioned above. By default, a local algorithm is used. To enable a global algorithm, set `use_local_init_data_cost` to `false` .

## ocl::StereoConstantSpaceBP::StereoConstantSpaceBP

Enables the `ocl::StereoConstantSpaceBP` constructors.

C++:`` `ocl::StereoConstantSpaceBP::``StereoConstantSpaceBP`(int ndisp=DEFAULT_NDISP, int iters=DEFAULT_ITERS, int levels=DEFAULT_LEVELS, int nr_plane=DEFAULT_NR_PLANE, int msg_type=CV_32F)

C++:`` `ocl::StereoConstantSpaceBP::``StereoConstantSpaceBP`(int ndisp, int iters, int levels, int nr_plane, float max_data_term, float data_weight, float max_disc_term, float disc_single_jump, int min_disp_th=0, int msg_type=CV_32F)

  Parameters: | ndisp – Number of disparities. iters – Number of BP iterations on each level. levels – Number of levels. nr_plane – Number of disparity levels on the first level. max_data_term – Truncation of data cost. data_weight – Data weight. max_disc_term – Truncation of discontinuity. disc_single_jump – Discontinuity single jump. min_disp_th – Minimal disparity threshold. msg_type – Type for messages. `CV_16SC1` and `CV_32FC1` types are supported.

`StereoConstantSpaceBP` uses a truncated linear model for the data cost and discontinuity terms:

DataCost = data \_ weight \cdot \min ( \lvert I_2-I_1 \rvert , max \_ data \_ term)

DiscTerm = \min (disc \_ single \_ jump \cdot \lvert f_1-f_2 \rvert , max \_ disc \_ term)

For more details, see [Yang2010].

By default, `StereoConstantSpaceBP` uses floating-point arithmetics and the `CV_32FC1` type for messages. But it can also use fixed-point arithmetics and the `CV_16SC1` message type for better performance. To avoid an overflow in this case, the parameters must satisfy the following requirement:

10 \cdot 2^{levels-1} \cdot max \_ data \_ term < SHRT \_ MAX

## ocl::StereoConstantSpaceBP::estimateRecommendedParams

Uses a heuristic method to compute parameters (ndisp, iters, levelsand nrplane) for the specified image size (widthand height).

C++:`` void `ocl::StereoConstantSpaceBP::``estimateRecommendedParams`(int width, int height, int& ndisp, int& iters, int& levels, int& nr_plane)

## ocl::StereoConstantSpaceBP::operator ()

Enables the stereo correspondence operator that finds the disparity for the specified rectified stereo pair.

C++:`` void `ocl::StereoConstantSpaceBP::``operator()`(const oclMat& left, const oclMat& right, oclMat& disparity)

  Parameters: | left – Left image. `CV_8UC1` , `CV_8UC3` and `CV_8UC4` types are supported. right – Right image with the same size and the same type as the left one. disparity – Output disparity map. If `disparity` is empty, the output type is `CV_16SC1` . Otherwise, the output type is `disparity.type()` .

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- ocl. OpenCL-accelerated Computer Vision »