crop_image_openCvCXX/main.cpp

#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/opencv.hpp>

#include <vector>
#include <algorithm>
#include <tuple>
#include <iostream>


using namespace cv;


struct comparator{
    bool operator() (std::tuple<std::vector<cv::Point>, bool, double> t1,
                     std::tuple<std::vector<cv::Point>, bool, double> t2) {
        return std::get<2>(t1) > std::get<2>(t2);
    }
} comparator;

int main(int, char**)
{
    // get image
    cv::Mat image = cv::imread("C:\\Users\\Sky\\Downloads\\name.png");
    cv::Mat grayImg;

    // convert to greyscale
    cv::cvtColor(image, grayImg, COLOR_BGRA2GRAY);

//    cv::Mat canny;
//    cv::Canny(grayImg,canny, 120, 255, 3);

    // finding threshes
    cv::Mat thresh;
    cv::threshold(grayImg,thresh, 127, 255, THRESH_BINARY_INV | THRESH_OTSU);


    // finding contours
    std::vector<std::vector<cv::Point>> contours;
    std::vector<cv::Vec4i> hierarchy;

    findContours( thresh, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE, Point(0, 0) );


    // finding max contour
    std::vector<std::tuple<std::vector<cv::Point>, bool, double>> vec;


    for(size_t i = 0; i < contours.size(); ++i){

        vec.push_back(std::make_tuple(contours.at(i), cv::isContourConvex(contours.at(i)),cv::contourArea(contours.at(i))));
    }

    std::sort(vec.begin(), vec.end(), comparator);

    std::tuple<std::vector<cv::Point>, bool, double> maxContour;
    maxContour = vec.at(0);



    // create mask
    cv::Mat mask = Mat::zeros(thresh.size(), CV_8U);

    for(size_t i = 0; i < contours.size(); ++i){
        cv::fillConvexPoly(mask, std::get<0>(vec.at(i)), Scalar(255,0,0),8,0);
    }

//    cv::fillConvexPoly(mask, std::get<0>(maxContour), Scalar(255,0,0),8,0);


    // bitwise
    cv::Mat res;
    cv::bitwise_and(image, image, res, mask);

    // show process
    imshow("result", res);
    imshow("mask", mask);
    imshow("canny", thresh);
    imshow("source", image);


    // create transparent background
    Mat dst;

    Mat rgb[3];
    split(res,rgb);

    Mat rgba[4]={rgb[0],rgb[1],rgb[2], mask};
    merge(rgba,4,dst);


    // save to file transparent and cropped images
    imwrite("C:/Documents/1.png", res);
    imwrite("C:/Documents/dst.png",dst);
    imwrite("C:/Documents/mask.png",mask);
    imwrite("C:/Documents/thresh.png",thresh);
    imwrite("C:/Documents/src.png",image);

    while (true) {
        if (waitKey() == 27) { //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
            std::cout << "esc key is pressed by user";
            break;
        }
    }

    return 0;

}