opencv关键点描述符矩阵的打印值

Question

我在打印通过使用任何opencv描述符提取器的“compute”方法获得的描述符矩阵的值时遇到了一些麻烦。我想逐个打印一个特征的描述符到一个文件，但总是当我访问带有'at'的描述符矩阵的某个元素时，我收到该元素的不同值。下面是一个'for'循环，我用来测试使用'at'时描述符矩阵的输出值：

for(int i=0; i<nF; i++){

    if(lpx != keypoints[i].pt.x && lpy != keypoints[i].pt.y){
        usedFeatures++;
        cerr << descriptors.row(i) << endl << endl; // printing row of descriptor matrix
        fileS << keypoints[i].pt.y << " " << keypoints[i].pt.x << " ";
        fileS << keypoints[i].size << " " << keypoints[i].angle << endl;

        if(i == nF - 2){
            //printing subvector of descriptor matrix made of the element at row i and col 0
            cerr << "get row i, col 0 " << descriptors.row(i).col(0) << endl;

            //same as before just inverting the order of access
            cerr << "get col 0, row i: " << descriptors.col(0).row(i) << endl;


            //printing the value of the element with 'at'
            cerr << (int)descriptors.at<uchar>(i, 0);

            //creating a new int and giving it the value of element (i, 0) of descriptor matrix. Should be the same
            //value shown on the subvector before
            int test = descriptors.at<uchar>(i, 0);

            //printing value of element
            cerr << "i, 0: " << test << endl;
        }

cerr << descriptors.row(i) << endl << endl;

[20, 11, 0, 18, 51, 3, 0, 3, 133, 50, 0, 0, 0, 0, 0, 11, 133, 18, 0, 0, 0, 0, 0, 3,
119, 2, 0, 0, 0, 0, 0, 2, 19, 5, 0, 4, 55, 27, 1, 1, 133, 25, 0, 1, 4, 1, 0, 22, 133,
18, 0, 0, 0, 0, 0, 14, 131, 13, 1, 0, 0, 0, 0, 1, 12, 1, 0, 1, 56, 133, 25, 13, 133,
14, 0, 0, 3, 8, 20, 80, 133, 38, 0, 0, 0, 0, 0, 51, 106, 11, 1, 0, 0, 0, 0, 23, 0, 0,
0, 0, 19, 126, 70, 11, 23, 0, 0, 0, 0, 9, 83, 133, 53, 1, 0, 0, 0, 0, 2, 133, 26, 
3, 2, 0, 0, 0, 0, 28]

和预期的一样，前两个打印在第二个“if”中：

cerr << "get row i, col 0 " << descriptors.row(i).col(0) << endl;

cerr << "get col 0, row i: " << descriptors.col(0).row(i) << endl;

给我[20]

但另外两个指纹

cerr << (int)descriptors.at<uchar>(i, 0);

int test = descriptors.at<uchar>(i, 0);
cerr << "i, 0: " << test << endl;

 0 0 160 65 0 0 48 65 0 0 0 0 0 0 144 65 0 0 76 66
 0 0 64 64 0 0 0 0 0 0 64 64 0 0 5 67 0 0 72 66
 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
 0 0 48 65 0 0 5 67 0 0 144 65 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0 0 0 0 0 0 64 64 0 0 238 66
 0 0 0 64 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 64

提前谢谢，抱歉我的英语和问题的大小。

Answer 1

找到答案了。这确实是一个类型问题。返回的描述符矩阵的类型不像我想的那样是uchar，它实际上是float。获取值

(float)descriptors.at<float>(i, 0);

给了我正确的价值。有趣的是，我发誓我以前试过浮车，但没有用。我肯定只试过int,double和unsigned int。