使用 OpenCV Cuda ORB 特征检测器

Posted 2023-03-13

【中文标题】使用 OpenCV Cuda ORB 特征检测器

【英文标题】：Using OpenCV Cuda ORB feature detector

【发布时间】：2018-04-21 21:08:08

【问题描述】：

我有一个应用程序，我正在接收一个图像流，我想在其中监控一组 ROI 内检测到的特征。这是使用 ORB 检测器完成的。在第一张图片中，我使用检测器来查找给定 ROI 的“参考”关键点和描述符。对于后续图像，我会找到相同 ROI 的“测试”关键点和描述符。然后我使用 knn 匹配器来查找引用和测试描述符之间的匹配。最后，我尝试找到“最佳”匹配，将关联的关键点添加到“匹配关键点”集合中，然后计算“匹配强度”。此匹配强度旨在指示在参考图像中找到的关键点与测试图像中的关键点的匹配程度。

我有几个问题：

1 - 这是对特征检测器的有效使用吗？我知道一个简单的模板匹配可能会给我类似的结果，但我希望避免光照轻微变化的问题。

2 - 我是否正确筛选“好”匹配项，然后我是否获得了与该匹配项正确关联的关键点？

3 - 我的代码似乎按原样工作，但是，如果我尝试使用流移动到 OpenCV 调用的异步版本，我会得到一个异常： “函数 cv::cuda::GpuMat::setTo 中的资源句柄无效”，这发生在对 ORB_Impl::buildScalePyramids 的调用（从 ORB_Impl::detectAndComputeAsync 调用）中。请参阅下面我的“NewFrame”函数的异步版本。这只是让我觉得我没有正确设置所有这些。

这是我的代码：

void Matcher::Matcher()

    // create ORB detector and descriptor matcher
    m_b = cuda::ORB::create(500, 1.2f, 8, 31, 0, 2, 0, 31, 20, true);   
    m_descriptorMatcher =       cv::cuda::DescriptorMatcher::createBFMatcher(cv::NORM_HAMMING); 


void Matcher::Configure(int imageWidth, int imageHeight, int roiX, int roiY, int roiW, int roiH)

    // set member variables
    m_imageWidth = imageWidth;
    m_imageHeight = imageHeight;
    m_roiX = roiX;
    m_roiY = roiY;
    m_roiW = roiW;
    m_roiH = roiH;

    m_GpuRefSet = false; // set flag indicating reference not yet set

    // create mask for specified ROI
    m_mask = GpuMat(imageHeight,imageWidth, CV_8UC1, Scalar::all(0));
    cv::Rect rect = cv::Rect(m_roiX, m_roiY, m_roiW, m_roiH);
    m_mask(rect).setTo(Scalar::all(255));       



double Matcher::NewFrame(void *pImagedata)

    // pImagedata = pointer to BGRA byte array
    // m_imageHeight and m_imageWidth have already been set
    // m_b is a pointer to the ORB detector

    if (!m_GpuRefSet)
     // 1st time through (after call to Matcher::Configure), set reference keypoints and descriptors

        cv::cuda::GpuMat mat1(m_imageHeight, m_imageWidth, CV_8UC4, pImagedata);  // put image data into GpuMat

        cv::cuda::cvtColor(mat1, m_refImage, CV_BGRA2GRAY); // convert to grayscale as required by ORB

        m_keyRef.clear(); // clear the vector<KeyPoint>, keypoint vector for reference image

        m_b->detectAndCompute(m_refImage, m_mask, m_keyRef, m_descRef, false); // detect keypoints and compute descriptors

        m_GpuRefSet = true;     
    

    cv::cuda::GpuMat mat2(m_imageHeight, m_imageWidth, CV_8UC4, pImagedata);  // put image data into GpuMat

    cv::cuda::cvtColor(mat2, m_testImage, CV_BGRA2GRAY, 0);  // convert to grayscale as required by ORB

    m_keyTest.clear(); // clear vector<KeyPoint>, keypoint vector for test image

    m_b->detectAndCompute(m_testImage, m_mask, m_keyTest, m_descTest, false);  // detect keypoints and compute descriptors


    double value = 0.0f;  // used to store return value ("match intensity")

        // calculate best match for each descriptor
        if (m_descTest.rows > 0)
           
            m_goodKeypoints.clear(); // clear vector of "good" KeyPoints, vector<KeyPoint> 

            m_descriptorMatcher->knnMatch(m_descTest, m_descRef, m_matches, 2, noArray());  // find matches

            // examine all matches, and collect the KeyPoints whose match distance mets given criteria
            for (int i = 0; i<m_matches.size(); i++)
                if (m_matches[i][0].distance < m_matches[i][1].distance * m_nnr) // m_nnr = nearest neighbor ratio (typically 0.6 - 0.8)
                    m_goodKeypoints.push_back(m_keyRef.at(m_matches[i][0].trainIdx));  // not sure if getting the correct keypoint here
                
            

            // calculate "match intensity", i.e. percent of the keypoints found in the reference image that are also in the test image
            value = ((double)m_goodKeypoints.size()) / ((double)m_keyRef.size());
        
        else
        
            value = 0.0f;
        

    return value;

这是失败的 NewFrame 函数的流/异步版本：

double Matcher::NewFrame(void *pImagedata)

    if (m_b.empty()) return 0.0f;

    if (!m_GpuRefSet)
    
        try
        
            cv::cuda::GpuMat mat1(m_imageHeight, m_imageWidth, CV_8UC4, pImagedata);

            cv::cuda::cvtColor(mat1, m_refImage, CV_BGRA2GRAY);

            m_keyRef.clear();

            m_b->detectAndComputeAsync(m_refImage, m_mask, m_keyRef, m_descRef, false,m_stream);  // FAILS HERE

            m_stream.waitForCompletion();

            m_GpuRefSet = true;
        
        catch (Exception e)
        
            string msg = e.msg;
        

    

    cv::cuda::GpuMat mat2(m_imageHeight, m_imageWidth, CV_8UC4, pImagedata);

    cv::cuda::cvtColor(mat2, m_testImage, CV_BGRA2GRAY, 0, m_stream);

    m_keyTest.clear();

    m_b->detectAndComputeAsync(m_testImage, m_mask, m_keyTest, m_descTest, false, m_stream);

    m_stream.waitForCompletion();

    double value = 0.0f;

    // calculate best match for each descriptor

    if (m_descTest.rows > 0)
    
        m_goodKeypoints.clear();
        m_descriptorMatcher->knnMatchAsync(m_descTest, m_descRef, m_matches, 2, noArray(), m_stream);

        m_stream.waitForCompletion(); 

        for (int i = 0; i<m_matches.size(); i++)
            if (m_matches[i][0].distance < m_matches[i][1].distance * m_nnr) // m_nnr = nearest neighbor ratio
            
                m_goodKeypoints.push_back(m_keyRef.at(m_matches[i][0].trainIdx));
            
        

        value = ((double)m_goodKeypoints.size()) / ((double)m_keyRef.size());
    
    else
    
        value = 0.0f;
    


    if (value > 1.0f) value = 1.0f;

    return value;

任何建议/建议将不胜感激。

谢谢！！

【参考方案1】：

经过一些试验，我确信这确实是 ORB 检测器的合理使用，而且我使用最近邻比方法对“好”的测试似乎也有效。这回答了上面的问题 #1 和 #2。

与问题 #3 相关，我确实发现了一些对我来说大有裨益的发现。

首先，事实证明我对 cv::cuda::Stream 和 cpu 线程不够小心。尽管我确信这对许多人来说是显而易见的，并且在 OpenCV 文档中有所提及，但任何放在特定 cv::cuda::Stream 上的东西都应该从同一个 cpu 线程中完成。不这样做不一定会产生异常，但会产生可能包含异常的未确定行为。

其次，对我来说，事实证明，使用异步版本的 detectAndCompute 和 knnMatch 在多线程中更可靠。这似乎与异步版本使用所有基于 GPU 的参数这一事实有关，其中非异步版本具有基于 CPU 的矢量参数。异步和非异步版本似乎都适用于我编写的简单单线程测试应用程序。但是，我的实际应用程序有其他 CUDA 内核和 CUDA 视频解码器在其他线程上运行，所以 GPU 上的东西很拥挤。

无论如何，这是我如何进行异步函数调用的版本，它为我清理了所有内容。它演示了 ORB 检测器和描述符匹配器的 Async/Stream 版本的使用。传递给它的 cv::cuda::Stream 可以是 cv::cuda::Stream::NullStream() 或您创建的 cv::cuda::Stream。请记住在使用它的同一 cpu 线程上创建流。

我仍然对改进建议感兴趣，但以下似乎可行。

orb = cuda::ORB::create(500, 1.2f, 8, 31, 0, 2, 0, 31, 20, true);   
matcher = cv::cuda::DescriptorMatcher::createBFMatcher(cv::NORM_HAMMING);  

// process 1st image
GpuMat imgGray1;  // load this with your grayscale image
GpuMat keys1; // this holds the keys detected
GpuMat desc1; // this holds the descriptors for the detected keypoints
GpuMat mask1; // this holds any mask you may want to use, or can be replace by noArray() in the call below if no mask is needed
vector<KeyPoint> cpuKeys1;  // holds keypoints downloaded from gpu

//ADD CODE TO LOAD imgGray1

orb->detectAndComputeAsync(imgGray1, mask1, keys1, desc1, false, m_stream);
stream.waitForCompletion();
orb->convert(keys1, cpuKeys1); // download keys to cpu if needed for anything...like displaying or whatever

// process 2nd image
GpuMat imgGray2;  // load this with your grayscale image
GpuMat keys2; // this holds the keys detected
GpuMat desc2; // this holds the descriptors for the detected keypoints
GpuMat mask2; // this holds any mask you may want to use, or can be replace by noArray() in the call below if no mask is needed
vector<KeyPoint> cpuKeys2;  // holds keypoints downloaded from gpu

//ADD CODE TO LOAD imgGray2

orb->detectAndComputeAsync(imgGray2, mask2, keys2, desc2, false, m_stream);
stream.waitForCompletion();
orb->convert(keys2, cpuKeys2); // download keys to cpu if needed for anything...like displaying or whatever

if (desc2.rows > 0)

    vector<vector<DMatch>> cpuKnnMatches;
    GpuMat gpuKnnMatches;  // holds matches on gpu
    matcher->knnMatchAsync(desc2, desc1, gpuKnnMatches, 2, noArray(), *stream);  // find matches
    stream.waitForCompletion();

    matcher->knnMatchConvert(gpuKnnMatches, cpuKnnMatches); // download matches from gpu and put into vector<vector<DMatch>> form on cpu

    vector<DMatch> matches;         // vector of good matches between tested images

    for (std::vector<std::vector<cv::DMatch> >::const_iterator it = cpuKnnMatches.begin(); it != cpuKnnMatches.end(); ++it) 
                if (it->size() > 1 && (*it)[0].distance / (*it)[1].distance < m_nnr)   // use Nearest-Neighbor Ratio to determine "good" matches
            DMatch m = (*it)[0];
            matches.push_back(m);       // save good matches here