OpenCV：透视变换/仿射变换

//@ 对棋盘格原图透视变换
    //@ 将棋盘格图像变换到屏幕大小，但是周边还是会有边框，图像中的屏幕是没有铺满的，误差
    Mat chessboard_warp;
    cv::warpPerspective(model_var.chessboard_image, chessboard_warp, model_var.warpMatrix, cv::Size(model_var.SCREEN_WIDTH, model_var.SCREEN_HEIGHT), cv::INTER_LINEAR, cv::BORDER_CONSTANT);
    //cv::warpPerspective(model_var.chessboard_image, chessboard_warp, model_var.warpMatrix, cv::Size(5000,5000), cv::INTER_LINEAR, cv::BORDER_CONSTANT);
    cv::namedWindow("chessboard_warp", cv::WINDOW_NORMAL);
    imshow("chessboard_warp", chessboard_warp);


    Mat chessboard_warp_Affine;
    chessboard_warp_Affine.create(model_var.SCREEN_WIDTH, model_var.SCREEN_HEIGHT, CV_16UC1);
    cv::Point2f chess_center;
    chess_center = (model_var.allCorners[17] + model_var.allCorners[24]) / 2;
    cv::Point2i chess_center_warp;
    chess_center_warp = transPoint(chess_center);

    //float offset_x = model_var.SCREEN_WIDTH / 2 - chess_center_warp.x;
    //float offset_y = model_var.SCREEN_HEIGHT / 2 - chess_center_warp.y;
    float offset_x = 800 / 2 - chess_center_warp.x;
    float offset_y = 700 / 2 - chess_center_warp.y;
    Mat trans_mat = (cv::Mat_(2, 3) << 1, 0, offset_x, 0, 1, offset_y);
    cv::warpAffine(chessboard_warp, chessboard_warp_Affine, trans_mat, cv::Size(800,700));
    cv::namedWindow("chessboard_warp_Affine", cv::WINDOW_NORMAL);
    imshow("chessboard_warp_Affine", chessboard_warp_Affine);

给定一个棋盘格图像，灰白色矩形大小为1000*2000，棋盘格在其中心，大小为700*800，每个棋盘格大小为100*100

 通过SB函数可以检测出所有角点，SB函数检测出的角点顺序是颠倒的，需要注意一下，然后就可以将角点坐标与角点在1000*2000中的实际坐标一一对应（这个实际坐标可以方便的推算出来），计算变换矩阵

void getWarpMatrix()
{
    vector dst_coners;
    int ini_x, ini_y;
    ini_x = model_var.CHESS_SIZE_W + (model_var.SCREEN_WIDTH - model_var.CHESS_SIZE_W * (model_var.chessboard_col + 1)) / 2;
    ini_y = model_var.CHESS_SIZE_H + (model_var.SCREEN_HEIGHT - model_var.CHESS_SIZE_H * (model_var.chessboard_row + 1)) / 2;
    
    Point2f tmp;
    for (int i = 0; i < model_var.chessboard_row; i++)
    {
        for (int j = 0; j < model_var.chessboard_col; j++)
        {
            tmp.x = ini_x + j * model_var.CHESS_SIZE_W;
            tmp.y = ini_y + i * model_var.CHESS_SIZE_H;
            dst_coners.push_back(tmp);

#ifdef DEBUG_TEST_IMSHOW_AND_PRINT
            cout << "[" << i << ", " << j << "] ==> (" << tmp.x << ", " << tmp.y << ")" << endl;
#endif // DEBUG_TEST_IMSHOW_AND_PRINT

        }
    }
    model_var.warpMatrix = cv::findHomography(model_var.allCorners, dst_coners);
}

将角点在图像上画出来

cv::drawChessboardCorners(drawChessboardImage, boardSize,
        imageCorners, found); // 找到的角点
cv::namedWindow("drawChessboardImage", cv::WINDOW_NORMAL);
cv::imshow("drawChessboardImage", drawChessboardImage);

进行透视变换，

//@ 对棋盘格原图透视变换
    //@ 将棋盘格图像变换到屏幕大小，但是周边还是会有边框，图像中的屏幕是没有铺满的，误差
    Mat chessboard_warp;
    cv::warpPerspective(model_var.chessboard_image, chessboard_warp, model_var.warpMatrix, cv::Size(model_var.SCREEN_WIDTH, model_var.SCREEN_HEIGHT), cv::INTER_LINEAR, cv::BORDER_CONSTANT);
    //cv::warpPerspective(model_var.chessboard_image, chessboard_warp, model_var.warpMatrix, cv::Size(5000,5000), cv::INTER_LINEAR, cv::BORDER_CONSTANT);
    cv::namedWindow("chessboard_warp", cv::WINDOW_NORMAL);
    imshow("chessboard_warp", chessboard_warp);

由于变换矩阵确定了，变换矩阵是由角点之间相互对应确定的，所以变换前后的原点也是对应的，上图中的红框，所以，不论warpPerspective函数中的那个Size参数如何变化，原点（0,0）不变。Size设为1000*2000的时候，刚好是棋盘格整图，假如Size设小点，则不会显示整个棋盘格图像

仿射变换，假如想在透视变换的基础上，截取棋盘格700*800的部分

Mat chessboard_warp_Affine;
    chessboard_warp_Affine.create(model_var.SCREEN_WIDTH, model_var.SCREEN_HEIGHT, CV_16UC1);
    cv::Point2f chess_center;
    chess_center = (model_var.allCorners[17] + model_var.allCorners[24]) / 2;
    cv::Point2i chess_center_warp;
    chess_center_warp = transPoint(chess_center);

    //float offset_x = model_var.SCREEN_WIDTH / 2 - chess_center_warp.x;
    //float offset_y = model_var.SCREEN_HEIGHT / 2 - chess_center_warp.y;
    float offset_x = 800 / 2 - chess_center_warp.x;
    float offset_y = 700 / 2 - chess_center_warp.y;
    Mat trans_mat = (cv::Mat_(2, 3) << 1, 0, offset_x, 0, 1, offset_y);
    cv::warpAffine(chessboard_warp, chessboard_warp_Affine, trans_mat, cv::Size(800,700));
    cv::namedWindow("chessboard_warp_Affine", cv::WINDOW_NORMAL);
    imshow("chessboard_warp_Affine", chessboard_warp_Affine);