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# Camera Calibration and 3D Reconstruction

## gpu::StereoBM_GPU

class `gpu::``StereoBM_GPU`

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

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

        enum { DEFAULT_NDISP = 64, DEFAULT_WINSZ = 19 };

        StereoBM_GPU();
        StereoBM_GPU(int preset, int ndisparities = DEFAULT_NDISP,
                     int winSize = DEFAULT_WINSZ);

        void operator() (const GpuMat& left, const GpuMat& right,
                         GpuMat& disparity, Stream& stream = Stream::Null());

        static bool checkIfGpuCallReasonable();

        int preset;
        int ndisp;
        int winSize;

        float avergeTexThreshold;

        ...
    };

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.

Note

- A basic stereo matching example can be found at opencv_source_code/samples/gpu/stereo_match.cpp
- A stereo matching example using several GPU’s can be found at opencv_source_code/samples/gpu/stereo_multi.cpp
- A stereo matching example using several GPU’s and driver API can be found at opencv_source_code/samples/gpu/driver_api_stereo_multi.cpp

## gpu::StereoBM_GPU::StereoBM_GPU

Enables `gpu::StereoBM_GPU` constructors.

C++:`` `gpu::StereoBM_GPU::``StereoBM_GPU`()

C++:`` `gpu::StereoBM_GPU::``StereoBM_GPU`(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.

## gpu::StereoBM_GPU::operator ()

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

C++:`` void `gpu::StereoBM_GPU::``operator()`(const GpuMat& left, const GpuMat& right, GpuMat& disparity, Stream& stream=Stream::Null())

  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.
  - stream – Stream for the asynchronous version.

## gpu::StereoBM_GPU::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 `gpu::StereoBM_GPU::``checkIfGpuCallReasonable`()

## gpu::StereoBeliefPropagation

class `gpu::``StereoBeliefPropagation`

Class computing stereo correspondence using the belief propagation algorithm.

    class 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_32F);
        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 GpuMat& left, const GpuMat& right,
                        GpuMat& disparity, Stream& stream = Stream::Null());
        void operator()(const GpuMat& data, GpuMat& disparity, Stream& stream = Stream::Null());

        int ndisp;

        int iters;
        int levels;

        float max_data_term;
        float data_weight;
        float max_disc_term;
        float disc_single_jump;

        int msg_type;

        ...
    };

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.

## gpu::StereoBeliefPropagation::StereoBeliefPropagation

Enables the `gpu::StereoBeliefPropagation` constructors.

C++:`` `gpu::StereoBeliefPropagation::``StereoBeliefPropagation`(int ndisp=DEFAULT_NDISP, int iters=DEFAULT_ITERS, int levels=DEFAULT_LEVELS, int msg_type=CV_32F)

C++:`` `gpu::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, `gpu::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

## gpu::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 `gpu::StereoBeliefPropagation::``estimateRecommendedParams`(int width, int height, int& ndisp, int& iters, int& levels)

## gpu::StereoBeliefPropagation::operator ()

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

C++:`` void `gpu::StereoBeliefPropagation::``operator()`(const GpuMat& left, const GpuMat& right, GpuMat& disparity, Stream& stream=Stream::Null())

C++:`` void `gpu::StereoBeliefPropagation::``operator()`(const GpuMat& data, GpuMat& disparity, Stream& stream=Stream::Null())

  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.
  - stream – Stream for the asynchronous version.

## gpu::StereoConstantSpaceBP

class `gpu::``StereoConstantSpaceBP`

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

    class 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 GpuMat& left, const GpuMat& right,
                        GpuMat& disparity, Stream& stream = Stream::Null());

        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;

        ...
    };

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` .

## gpu::StereoConstantSpaceBP::StereoConstantSpaceBP

Enables the `gpu::StereoConstantSpaceBP` constructors.

C++:`` `gpu::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++:`` `gpu::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

## gpu::StereoConstantSpaceBP::estimateRecommendedParams

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

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

## gpu::StereoConstantSpaceBP::operator ()

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

C++:`` void `gpu::StereoConstantSpaceBP::``operator()`(const GpuMat& left, const GpuMat& right, GpuMat& disparity, Stream& stream=Stream::Null())

  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()` .
  - stream – Stream for the asynchronous version.

## gpu::DisparityBilateralFilter

class `gpu::``DisparityBilateralFilter`

Class refining a disparity map using joint bilateral filtering.

    class CV_EXPORTS DisparityBilateralFilter
    {
    public:
        enum { DEFAULT_NDISP  = 64 };
        enum { DEFAULT_RADIUS = 3 };
        enum { DEFAULT_ITERS  = 1 };

        explicit DisparityBilateralFilter(int ndisp = DEFAULT_NDISP,
            int radius = DEFAULT_RADIUS, int iters = DEFAULT_ITERS);

        DisparityBilateralFilter(int ndisp, int radius, int iters,
            float edge_threshold, float max_disc_threshold,
            float sigma_range);

        void operator()(const GpuMat& disparity, const GpuMat& image,
                        GpuMat& dst, Stream& stream = Stream::Null());

        ...
    };

The class implements [Yang2010] algorithm.

## gpu::DisparityBilateralFilter::DisparityBilateralFilter

Enables the `gpu::DisparityBilateralFilter` constructors.

C++:`` `gpu::DisparityBilateralFilter::``DisparityBilateralFilter`(int ndisp=DEFAULT_NDISP, int radius=DEFAULT_RADIUS, int iters=DEFAULT_ITERS)

C++:`` `gpu::DisparityBilateralFilter::``DisparityBilateralFilter`(int ndisp, int radius, int iters, float edge_threshold, float max_disc_threshold, float sigma_range)

  Parameters:

  - ndisp – Number of disparities.
  - radius – Filter radius.
  - iters – Number of iterations.
  - edge_threshold – Threshold for edges.
  - max_disc_threshold – Constant to reject outliers.
  - sigma_range – Filter range.

## gpu::DisparityBilateralFilter::operator ()

Refines a disparity map using joint bilateral filtering.

C++:`` void `gpu::DisparityBilateralFilter::``operator()`(const GpuMat& disparity, const GpuMat& image, GpuMat& dst, Stream& stream=Stream::Null())

  Parameters:

  - disparity – Input disparity map. `CV_8UC1` and `CV_16SC1` types are supported.
  - image – Input image. `CV_8UC1` and `CV_8UC3` types are supported.
  - dst – Destination disparity map. It has the same size and type as `disparity` .
  - stream – Stream for the asynchronous version.

## gpu::drawColorDisp

Colors a disparity image.

C++:`` void `gpu::``drawColorDisp`(const GpuMat& src_disp, GpuMat& dst_disp, int ndisp, Stream& stream=Stream::Null())

  Parameters:

  - src_disp – Source disparity image. `CV_8UC1` and `CV_16SC1` types are supported.
  - dst_disp – Output disparity image. It has the same size as `src_disp` . The type is `CV_8UC4` in `BGRA` format (alpha = 255).
  - ndisp – Number of disparities.
  - stream – Stream for the asynchronous version.

This function draws a colored disparity map by converting disparity values from `[0..ndisp)` interval first to `HSV` color space (where different disparity values correspond to different hues) and then converting the pixels to `RGB` for visualization.

## gpu::reprojectImageTo3D

Reprojects a disparity image to 3D space.

C++:`` void `gpu::``reprojectImageTo3D`(const GpuMat& disp, GpuMat& xyzw, const Mat& Q, int dst_cn=4, Stream& stream=Stream::Null())

  Parameters:

  - disp – Input disparity image. `CV_8U` and `CV_16S` types are supported.
  - xyzw – Output 3- or 4-channel floating-point image of the same size as `disp` . Each element of `xyzw(x,y)` contains 3D coordinates `(x,y,z)` or `(x,y,z,1)` of the point `(x,y)` , computed from the disparity map.
  - Q – 4 \times 4 perspective transformation matrix that can be obtained via `stereoRectify()` .
  - dst_cn – The number of channels for output image. Can be 3 or 4.
  - stream – Stream for the asynchronous version.

See also

`reprojectImageTo3D()`

## gpu::solvePnPRansac

Finds the object pose from 3D-2D point correspondences.

C++:`` void `gpu::``solvePnPRansac`(const Mat& object, const Mat& image, const Mat& camera_mat, const Mat& dist_coef, Mat& rvec, Mat& tvec, bool use_extrinsic_guess=false, int num_iters=100, float max_dist=8.0, int min_inlier_count=100, vector<int>* inliers=NULL)

  Parameters:

  - object – Single-row matrix of object points.
  - image – Single-row matrix of image points.
  - camera_mat – 3x3 matrix of intrinsic camera parameters.
  - dist_coef – Distortion coefficients. See `undistortPoints()` for details.
  - rvec – Output 3D rotation vector.
  - tvec – Output 3D translation vector.
  - use_extrinsic_guess – Flag to indicate that the function must use `rvec` and `tvec` as an initial transformation guess. It is not supported for now.
  - num_iters – Maximum number of RANSAC iterations.
  - max_dist – Euclidean distance threshold to detect whether point is inlier or not.
  - min_inlier_count – Flag to indicate that the function must stop if greater or equal number of inliers is achieved. It is not supported for now.
  - inliers – Output vector of inlier indices.

See also

`solvePnPRansac()`

[Felzenszwalb2006] | (1, 2) Pedro F. Felzenszwalb algorithm [Pedro F. Felzenszwalb and Daniel P. Huttenlocher. Efficient belief propagation for early vision. International Journal of Computer Vision, 70(1), October 2006

[Yang2010]

(1, 2, 3)

17. Yang, L. Wang, and N. Ahuja. A constant-space belief propagation algorithm for stereo matching. In CVPR, 2010.

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