[Image Stitching] How to stitch images using opencv library in c++

[Github Result]

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[Reference Site]

• Stitching related

[ https://www.geeksforgeeks.org/stitching-input-images-panorama-using-opencv-c/ ]
[ https://www.pyimagesearch.com/2018/12/17/image-stitching-with-opencv-and-python/ ]

• Compile C++ related

[ https://www.cyberciti.biz/faq/howto-compile-and-run-c-cplusplus-code-in-linux/ ]
[ https://stackoverflow.com/questions/48687259/undefined-reference-to-cvimreadcvstring-const-int ]

• Opencv related

[ https://diyver.tistory.com/51 ]
[ https://stackoverflow.com/questions/34497099/opencv-undefined-reference-to-imread ]

[ https://answers.opencv.org/question/221603/undefined-reference-to-imread/ ]

[ https://learnopencv.com/image-resizing-with-opencv/ ]

• Time duration related

[ https://www.geeksforgeeks.org/measure-execution-time-function-cpp/ ]

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[Code]

• 다음과 같은 opencv library들을 포함: imgcodecs, highgui, stitching

#include <iostream>
#include <fstream>

// Time duration related
#include <chrono>

// stitching related
#include "opencv2/imgcodecs/imgcodecs.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/stitching.hpp"

// Original Image Size: width * height = 4032 * 1908
bool RESIZE = false;

int main()
{
    // To check time
    auto start = std::chrono::high_resolution_clock::now();

    // Define mode for stitching as panorama
    cv::Stitcher::Mode mode = cv::Stitcher::PANORAMA;

    // Road images
    cv::Mat left = cv::imread("/home/sj/iros2022/image/left.jpg", 1);
    cv::Mat front = cv::imread("/home/sj/iros2022/image/front.jpg", 1);
    cv::Mat right = cv::imread("/home/sj/iros2022/image/right.jpg", 1);

    // Check image read correctly
    if(left.cols != 0)
        std::cout << "Correctly read left image !!" << std::endl;
    if(front.cols != 0)
        std::cout << "Correctly read front image !!" << std::endl;
    if(right.cols != 0)
        std::cout << "Correctly read right image !!" << std::endl;

    // Resize image 
    double height = left.cols / 4;
    double width = left.rows / 4;

    // Combine three images in one vector 
    std::vector<cv::Mat> imgs;
    imgs.push_back(left);
    imgs.push_back(front);
    imgs.push_back(right);

    // Initialization output image
    cv::Mat panorama;

    // Make panorama image using cv::Stitcher 
    cv::Ptr<cv::Stitcher> stitcher = cv::Stitcher::create(mode, false);
    cv::Stitcher::Status status = stitcher->stitch(imgs, panorama);

    // If we want to change image size, then please change variable "RESIZE" **false** to **true** !!
    if(RESIZE)
        cv::resize(panorama, panorama, cv::Size(height, width), CV_INTER_LINEAR);

    // Check time duration
    auto finish = std::chrono::high_resolution_clock::now();
    auto duration = std::chrono::duration_cast<std::chrono::microseconds>(finish - start);
    std::cout << "Time duration: " << (double)duration.count() / 1000000 << " sec" << std::endl;

    // Write and show result image 
    cv::imwrite("~/image/result.jpg", panorama);
    cv::imshow("Result", panorama);

    // Wait image not auto cancel
    cv::waitKey(0);

    return 0;
}

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[Compile]

• C++을 사용하였고 3개의 라이브러리를 포함하고 있으므로 stitching 이라는 이름을 가진 exeutive file을 만들어줌

g++ stitching.cpp -L/usr/local/include/opencv2 -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lopencv_core -lopencv_stitching -o stitching

• • g++: c++ & gcc: c
  • stitching.cpp: 현재 저장되어 있는 코드의 이름
  • -L: 포함된 라이브러리가 있는 경로
  • -lopencv_~: 코드에 포함된 라이브러리들
  • -o: 실행파일에 대한 정보를 입력할 flag
  • stitching: 실행파일의 이름

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[Run]

• 해당 파일에 다음과 같이 작성해주면 컴파일한 코드를 빌드 및 실행

# Example of current path: ~/src/Stitching
./stitching

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[Output]

• Input images

Left	Front	Right

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• Output image

RESIZE == true (원래 이미지 크기의 1/4배)

RESIZE == False

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[Analyze]

• 확실히 resize를 하게 되면 linear interpolation을 하기 때문에 영상의 resolution이 좋아지지 않음 (되도록이면 영상의 크기를 보존하는 것이 좋음)