CODEWITHSUNDEEP
c++opencvsift
tqjustc
tqjustc

Reputation: 3814

how to use SIFT in opencv

I am learning C++ and OpenCV these days. Given an image, I want to extract its SIFT features. From http://docs.opencv.org/modules/nonfree/doc/feature_detection.html, we can know that OpenCV 2.4.8 has the SIFT module. See here: enter image description here

But I do not know how to use it. Currently, to use SIFT, I need to first call the class SIFT to get a SIFT instance. Then, I need to use SIFT::operator()() to do SIFT.

But what is OutputArray , InputArray, KeyPoint? Could anyone give a demo to show how to use SIFT class to do SIFT?

Upvotes: 15

Views: 66992

Answers (5)

Marian
Marian

Reputation: 7472

Update for OpenCv 4.5 and those who (like me) do not know quickly translate @mcy 's comment to code.

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/features2d.hpp>

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

    cv::Ptr<cv::SIFT> siftPtr = cv::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);

    return 0;
}

Upvotes: 0

Julien Busset
Julien Busset

Reputation: 315

Update for OpenCV 4.2.0 (don’t forget to link opencv_xfeatures2d420.lib, of course)

#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;
}

Upvotes: 7

Yirga
Yirga

Reputation: 881

I was having the same question for opencv3 but i found this. It explains why SIFT and SURF removed from the default install of OpenCV 3.0 and how to use SIFT and SURF in OpenCV 3.

The algorithms and associated implementations in opencv_contrib are not installed by default and you need to explicitly enable them when compiling and installing OpenCV to obtain access to them.

They are move to xfeatures2d library.
#include <opencv2/xfeatures2d.hpp>

Upvotes: 0

andrewchan2022
andrewchan2022

Reputation: 5290

update for OpenCV3

#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;
}

Upvotes: 5

Liam McInroy
Liam McInroy

Reputation: 4356

See the example from Sift implementation with OpenCV 2.2

#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;
}

Tested on OpenCV 2.4.8

Upvotes: 18

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