using StereoBM in java on Android -> some results

edit

Hello is someone could give me an example to show how to use org.opencv.calib3d.StereoBM in Java (on Android in my case) ? I only found examples in C++ and Python on the web...

EDIT2 : I tried to calibrate one camera before trying to calibrate both. So I wrote the following java code :

init variables :

        imageCorners = new MatOfPoint2f();
        savedImage = new Mat();
        imagePoints = new ArrayList<>();
        objectPoints = new ArrayList<>();
        intrinsic = new Mat(3, 3, CvType.CV_32FC1);
        distCoeffs = new Mat();
        boardSize = new Size(numCornersHor, numCornersVer);
        obj = new MatOfPoint3f();
        for (int j = 0; j < numSquares; j++)
            obj.push_back(new MatOfPoint3f(new Point3(j / numCornersHor, j % numCornersVer, 0.0f)));

In the main loop :

                if (!isCalibrated) {
                    if (touch_screen_down) {
                        Mat grayImage = new Mat(rgba.size(), CvType.CV_8UC1);
                        Imgproc.cvtColor(rgba, grayImage, Imgproc.COLOR_BGR2GRAY);

                        boolean found = Calib3d.findChessboardCorners(
                                grayImage, boardSize, imageCorners,
                                Calib3d.CALIB_CB_ADAPTIVE_THRESH + Calib3d.CALIB_CB_NORMALIZE_IMAGE + Calib3d.CALIB_CB_FAST_CHECK);

                        if (found && successes <= boardsNumber) {
                            // optimization
                            TermCriteria term = new TermCriteria(TermCriteria.EPS | TermCriteria.MAX_ITER, 30, 0.001);
                            Imgproc.cornerSubPix(grayImage, imageCorners,
                                    new Size(11, 11), new Size(-1, -1), term);

                            // save the current frame for further elaborations
                            grayImage.copyTo(savedImage);

                            // show the chessboard inner corners on screen
                            Calib3d.drawChessboardCorners(rgba, boardSize,
                                    imageCorners, found);

                            imagePoints.add(imageCorners);
                            imageCorners = new MatOfPoint2f();
                            objectPoints.add(obj);
                            successes++;
                        }

                        if (successes == boardsNumber) {
                            List<Mat> rvecs = new ArrayList<>();
                            List<Mat> tvecs = new ArrayList<>();
                            intrinsic.put(0, 0, 1);
                            intrinsic.put(1, 1, 1);

                            calib_error = Calib3d.calibrateCamera(objectPoints, imagePoints, savedImage.size(), intrinsic, distCoeffs, rvecs, tvecs);
                            isCalibrated = true;
                        }
                    }
                }
                else {   // is already calibrated so undistord the picture
                    Mat undistored = new Mat();
                    Imgproc.undistort(rgba, undistored, intrinsic, distCoeffs);
                    undistored.copyTo(rgba);
                }

BUT the calibration error (calib_error) is bad when I run this code with 20 pictures of a chessboard : values are between 150 and 200. I read that the calibration error should be less than 0.5 !! And when calibration is done, news pictures from my camera are very distorded... What is the problem ?

EDIT1 : I wrote the following java code :

                // load left and right images
                Mat rgba_left = Utils.loadResource(
                        MainActivity.this, 
                        R.drawable.trampoline3d_gauche,
                        Imgcodecs.CV_LOAD_IMAGE_COLOR);
                Mat rgba_right = Utils.loadResource(
                        MainActivity.this, 
                        R.drawable.trampoline3d_droite,
                        Imgcodecs.CV_LOAD_IMAGE_COLOR);

                // create matrix with 1 channel
                Mat mleft= new Mat(rgba_left.size(), CvType.CV_8UC1);
                Mat mright= new Mat(rgba_right.size(), CvType.CV_8UC1);
                Mat mdisparity= new Mat(rgba_left.size(), CvType.CV_8UC1);

                // convert images to gray scale
                Imgproc.cvtColor(rgba_left, mleft, Imgproc.COLOR_BGR2GRAY);
                Imgproc.cvtColor(rgba_right, mright, Imgproc.COLOR_BGR2GRAY);

                StereoBM stereo = StereoBM.create(16*5, 21);
                stereo.setPreFilterSize(5);
                stereo.setPreFilterCap(61);
                stereo.setMinDisparity(-10);
                stereo.setNumDisparities(16*5);
                stereo.setTextureThreshold(300);
                stereo.setUniquenessRatio(5);
                stereo.setSpeckleWindowSize(0);
                stereo.setSpeckleRange(8);

                stereo.compute(mleft, mright, mdisparity);

                // normalize from float to bytes
                Core.normalize(mdisparity,rgba_right,0,255,Core.NORM_MINMAX,CvType.CV_8UC1);

                // display the result
                Imgproc.cvtColor(rgba_right, rgba_left, Imgproc.COLOR_GRAY2BGRA, 4);
                Imgproc.resize(rgba_left, rgba, rgba.size());

but I obtain poor result ...

left image :

right image :

result :