如何在opencv中使用SIFT

Question

这些天我正在学习C++和OpenCV。给定一幅图像，我想提取它的SIFT特征。从http://docs.opencv.org/modules/nonfree/doc/feature_detection.html我们可以知道OpenCV 2.4.8有SIFT模块。请看这里：

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但是我不知道如何使用它。目前，要使用SIFT，我需要首先调用SIFT类来获取SIFT实例。然后，我需要使用SIFT::operator()()来做筛选。

但是什么是OutputArray，InputArray，KeyPoint呢？谁能演示一下如何使用SIFT类来做SIFT？

Answer 1

请参阅来自Sift implementation with OpenCV 2.2的示例

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/nonfree/features2d.hpp> //Thanks to Alessandro

int main(int argc, const char* argv[])
{
    const cv::Mat input = cv::imread("input.jpg", 0); //Load as grayscale

    cv::SiftFeatureDetector detector;
    std::vector<cv::KeyPoint> keypoints;
    detector.detect(input, keypoints);

    // Add results to image and save.
    cv::Mat output;
    cv::drawKeypoints(input, keypoints, output);
    cv::imwrite("sift_result.jpg", output);

    return 0;
}

在OpenCV 2.4.8上测试

Answer 2

OpenCV 4.2.0的更新(当然，不要忘记链接opencv_xfeatures2d420.lib )

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/xfeatures2d.hpp>

int main(int argc, char** argv)
{
    const cv::Mat input = cv::imread("input.jpg", 0); //Load as grayscale

    cv::Ptr<cv::xfeatures2d::SIFT> siftPtr = cv::xfeatures2d::SIFT::create();
    std::vector<cv::KeyPoint> keypoints;
    siftPtr->detect(input, keypoints);

    // Add results to image and save.
    cv::Mat output;
    cv::drawKeypoints(input, keypoints, output);
    cv::imwrite("sift_result.jpg", output);it.

    return 0;
}

Answer 3

OpenCV3更新

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/nonfree/features2d.hpp> //Thanks to Alessandro

int main(int argc, const char* argv[])
{
    const cv::Mat input = cv::imread("input.jpg", 0); //Load as grayscale

    cv::Ptr<cv::SiftFeatureDetector> detector = cv::SiftFeatureDetector::create();
    std::vector<cv::KeyPoint> keypoints;
    detector->detect(input, keypoints);

    // Add results to image and save.
    cv::Mat output;
    cv::drawKeypoints(input, keypoints, output);
    cv::imwrite("sift_result.jpg", output);

    return 0;
}