C++ 提取图像ROI保存到Mat

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只要给定待提取ROI的四个角点坐标，利用OpenCV的透视变换计算出变换矩阵，就可以实现提取并保存到Mat；

void ls::getROI(cv::Mat &src, float vertices[8],cv::Mat &dst)    {        float w2 = sqrt(pow(vertices[0] - vertices[2], 2) + pow(vertices[1] - vertices[3] ,2 ));        float h2 = sqrt(pow(vertices[0] - vertices[4], 2) + pow(vertices[1] - vertices[5] ,2));        dst = cv::Mat::zeros(h2, w2, CV_8UC3);                //__android_log_print(ANDROID_LOG_INFO, "SRC", "error%d", src.rows);                        // corners of destination image with the sequence [tl, tr, bl, br]        vector<Point2f> dst_pts, img_pts;        dst_pts.push_back(cv::Point(0, 0));        dst_pts.push_back(cv::Point(w2 - 1, 0));        dst_pts.push_back(cv::Point(0, h2 - 1));        dst_pts.push_back(cv::Point(w2 - 1, h2 - 1));                // corners of source image with the sequence [tl, tr, bl, br]        img_pts.push_back(cv::Point(vertices[0], vertices[1]));        img_pts.push_back(cv::Point(vertices[2],vertices[3]));        img_pts.push_back(cv::Point(vertices[4],vertices[5]));        img_pts.push_back(cv::Point(vertices[6], vertices[7]));                                // convert to original image scale        //    for (size_t i = 0; i < img_pts.size(); i++) {        //        img_pts[i].x *= scale;        //        img_pts[i].y *= scale;        //    }                // get transformation matrix        cv::Mat M_trans = getPerspectiveTransform(img_pts, dst_pts);                // apply perspective transformation        warpPerspective(src, dst, M_trans, dst.size());    }

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