OpenCV-将FLANN与ORB描述符配合使用以匹配功能 [英] OpenCV - Use FLANN with ORB descriptors to match features

问题描述

我正在使用OpenCV 3.2

I am using OpenCV 3.2

我正在尝试使用FLANN以比蛮力更快的方式匹配特征描述符.

I am trying to use FLANN to match features descriptors in a faster way than brute force.

// Ratio to the second neighbor to consider a good match.
#define RATIO    0.75

void matchFeatures(const cv::Mat &query, const cv::Mat &target,
                   std::vector<cv::DMatch> &goodMatches) {
    std::vector<std::vector<cv::DMatch>> matches;
    cv::Ptr<cv::FlannBasedMatcher> matcher = cv::FlannBasedMatcher::create();
    // Find 2 best matches for each descriptor to make later the second neighbor test.
    matcher->knnMatch(query, target, matches, 2);
    // Second neighbor ratio test.
    for (unsigned int i = 0; i < matches.size(); ++i) {
        if (matches[i][0].distance < matches[i][1].distance * RATIO)
            goodMatches.push_back(matches[i][0]);
    }
}

此代码可用于SURF和SIFT描述符，但不适用于ORB.

This code is working me with SURF and SIFT descriptors, but not with ORB.

OpenCV Error: Unsupported format or combination of formats (type=0) in buildIndex

正如在此处所述，FLANN需要描述符为CV_32F类型，因此我们需要转换它们.

As it's said here, FLANN needs the descriptors to be of type CV_32F so we need to convert them.

if (query.type() != CV_32F) query.convertTo(query, CV_32F);
if (target.type() != CV_32F) target.convertTo(target, CV_32F);

但是，这种假定的修复方法使我在convertTo函数中返回了另一个错误.

However, this supposed fix is returning me another error in convertTo function.

OpenCV Error: Assertion failed (!fixedType() || ((Mat*)obj)->type() == mtype) in create

此断言在opencv/modules/core/src/matrix.cpp文件的第2277行中.

This assertion is in opencv/modules/core/src/matrix.cpp file, line 2277.

发生了什么事?

用于复制问题的代码.

#include <opencv2/opencv.hpp>

int main(int argc, char **argv) {
    // Read both images.
    cv::Mat image1 = cv::imread(argv[1], cv::IMREAD_GRAYSCALE);
    if (image1.empty()) {
        std::cerr << "Couldn't read image in " << argv[1] << std::endl;
        return 1;
    }
    cv::Mat image2 = cv::imread(argv[2], cv::IMREAD_GRAYSCALE);
    if (image2.empty()) {
        std::cerr << "Couldn't read image in " << argv[2] << std::endl;
        return 1;
    }
    // Detect the keyPoints and compute its descriptors using ORB Detector.
    std::vector<cv::KeyPoint> keyPoints1, keyPoints2;
    cv::Mat descriptors1, descriptors2;
    cv::Ptr<cv::ORB> detector = cv::ORB::create();
    detector->detectAndCompute(image1, cv::Mat(), keyPoints1, descriptors1);
    detector->detectAndCompute(image2, cv::Mat(), keyPoints2, descriptors2);
    // Match features.
    std::vector<cv::DMatch> matches;
    matchFeatures(descriptors1, descriptors2, matches);
    // Draw matches.
    cv::Mat image_matches;
    cv::drawMatches(image1, keyPoints1, image2, keyPoints2, matches, image_matches);
    cv::imshow("Matches", image_matches);
}

推荐答案

您是否调整了FLANN参数?

Did you adjust the FLANN parameters?

来自 http://docs.opencv. org/3.0-beta/doc/py_tutorials/py_feature2d/py_matcher/py_matcher.html

在使用ORB时，您可以传递以下内容.根据文档建议使用带注释的值，但在某些情况下并不能提供必需的结果.其他值工作正常.

While using ORB, you can pass the following. The commented values are recommended as per the docs, but it didn’t provide required results in some cases. Other values worked fine.:

index_params = dict(算法= FLANN_INDEX_LSH， table_number = 6，#12 key_size = 12，#20 multi_probe_level = 1)#2

index_params= dict(algorithm = FLANN_INDEX_LSH, table_number = 6, # 12 key_size = 12, # 20 multi_probe_level = 1) #2

可能您可以将其转换为C ++ API?

Probably you can convert that to C++ api?

根据评论，C ++方式为:

According to the comment, the C++ way is:

cv::FlannBasedMatcher matcher = cv::FlannBasedMatcher(cv::makePtr<cv::flann::LshIndexParams>(12, 20, 2));

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