c++ - Opencv Flannbasedmatcher

Question

我遇到了一个问题: CV::FlannBasedMatcher 更准确地说，使用 knnMatch 方法。 我的程序将 IplImage* 作为输入并检测人脸，然后切割人脸并将创建的人脸与我计算机上存储的图像进行比较。如果我得到超过 10 个良好匹配，它会写入标准输出匹配。

加载的图像不是灰度图像。这很重要吗？

我的问题是它可以工作，但时间是随机的，从 1 分钟到 3 分钟不等。

错误消息总是出现在 knnMatch 方法上。它们在这里(注意每次只有一个):

OpenCV Error: Assertion failed ((globalDescIdx>=0) && (globalDescIdx < size())) in           getLocalIdx, file    /opt/local/var/macports/build/_opt_mports_dports_graphics_opencv/opencv/work/opencv-  2.4.9/modules/features2d/src/matchers.cpp, line 163
 libc++abi.dylib: terminating with uncaught exception of type cv::Exception:   /opt/local/var/macports/build/_opt_mports_dports_graphics_opencv/opencv/work/opencv-2.4.9/modules/features2d/src/matchers.cpp:163: error: (-215) (globalDescIdx>=0) && (globalDescIdx < size()) in function getLocalIdx

我不明白为什么抛出这个异常...

这是我的代码:

int        DroneCV::matchFaces()
{
std::vector<cv::KeyPoint> keypointsO;
std::vector<cv::KeyPoint> keypointsS;
cv::Mat descriptors_object, descriptors_scene;
cv::Mat foundFaces(this->_faceCut);
cv::FlannBasedMatcher matcher;
std::vector<std::vector<cv::DMatch>> matches;
std::vector<cv::DMatch> good_matches;
cv::SurfDescriptorExtractor extractor;
cv::SurfFeatureDetector surf(this->_minHessian);

surf.detect(foundFaces,keypointsS);
surf.detect(this->_faceToRecognize,keypointsO);
if (!this->_faceToRecognize.data || !foundFaces.data)
{
    this->log("Fail to init data in DronceCV::matchFaces");
    return (0);
}

extractor.compute(foundFaces, keypointsS, descriptors_scene);
extractor.compute(this->_faceToRecognize, keypointsO, descriptors_object);

if(descriptors_scene.empty())//descriptors_scene.type()!=CV_32F)
{
    this->log("Descriptor got wrong type");
    descriptors_scene.convertTo(descriptors_scene, CV_32F);
    return 0;
 }
if(descriptors_object.type()!=CV_32F || descriptors_scene.type()!=CV_32F)
{
    this->log("TYPE OBJECT " + std::to_string(descriptors_object.type()));
    this->log("TYPE SCENE " + std::to_string(descriptors_scene.type()));
    return (0);
}
//Both image must be in grayscale ???
try {
    matcher.knnMatch( descriptors_object, descriptors_scene, matches, 5 ); // find the 2 nearest neighbors

} catch (cv::Exception e) {
    this->log(e.err);
}
good_matches.reserve(matches.size());
for (size_t i = 0; i < matches.size(); ++i)
{
    if (matches[i].size() < 2)
        continue;
    const cv::DMatch &m1 = matches[i][0];
    const cv::DMatch &m2 = matches[i][1];

    if(m1.distance <= this->_nndrRatio * m2.distance)
        good_matches.push_back(m1);
}
this->log("Number of good matches" + std::to_string(good_matches.size()));
foundFaces.release();
if (good_matches.size() > 8)
    return (1);
else
    return (0);

void        DroneCV::analyzeFrame(IplImage *img)
{
if (!img)
{
    this->log("Frame empty");
    return;
}

if (this->detectFaces(img) == 1)
{
    if (this->matchFaces() == 1)
    {
        this->log("Matched");
        cvReleaseImage(&this->_faceCut);
    }
}
}

预先感谢您的帮助

Answer 1

我也遇到了这个问题，我花了将近 3-4 个小时才弄明白。当您应用 knn match 时，请确保测试图像和查询图像中的特征数量大于或等于 knn 匹配中的最近邻居数量。
比如说，我们有这样的代码:

Mat img1,img2,desc1,desc2;
vector<KeyPoint> kpt1,kpt2;

FAST(img1,kpt1,30,true) ;
FAST(img2,kpt1,30,true) ;

SurfDescriptorExtractor sfdesc1,sfdesc2;
sfdesc1.compute(img1,kpt1,desc1);
sfdesc2.compute(img2,kpt2,desc2);

FlannBasedMatcher matcher;
vector< vector<DMatch> > matches1,matches2;
matcher.knnMatch(desc1,desc2,matches1,2);

这段代码会像文章中那样返回异常，只需修改代码如下:

if(kpt1.size()>=2 && kpt2.size()>=2) 
matcher.knnMatch(desc1,desc2,matches1,2);

这个方法对我有用..!!