如何在ios中将cv :: Mat转换为json格式

Question

-(void) processImage:(cv::Mat &)image{

    cvtColor(image, img2, CV_BGR2GRAY);

    orb -> detect(img2, keypoints1);

    orb -> compute(img2, keypoints1, descriptors1);

    drawKeypoints(img2, keypoints1, outImage);

}

OutImage采用cv :: Mat格式。如何使用openCV ORB算法将其转换为NSDictionary格式。