我的opencv2的imread为什么不运作?

Question

为什么imread总是报错[ WARN:0@0.165] global loadsave.cpp:248 cv::findDecoder imread_(''): can't open/read file: check file path/integrity

#include <iostream>
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>

int Otsu(cv::Mat& src, cv::Mat& dst, int thresh) {
    const int Grayscale = 256;
    int graynum[Grayscale] = { 0 };
    int r = src.rows;
    int c = src.cols;
    for (int i = 0; i < r; ++i) {
        const uchar* ptr = src.ptr<uchar>(i);
        for (int j = 0; j < c; ++j) {        //直方图统计
            graynum[ptr[j]]++;
        }
    }

    double P[Grayscale] = { 0 };
    double PK[Grayscale] = { 0 };
    double MK[Grayscale] = { 0 };
    double srcpixnum = r * c, sumtmpPK = 0, sumtmpMK = 0;
    for (int i = 0; i < Grayscale; ++i) {
        P[i] = graynum[i] / srcpixnum;   //每个灰度级出现的概率
        PK[i] = sumtmpPK + P[i];         //概率累计和 
        sumtmpPK = PK[i];
        MK[i] = sumtmpMK + i * P[i];       //灰度级的累加均值                                                                                                                                                                                                                                                                                                                                                                                                        
        sumtmpMK = MK[i];
    }

    //计算类间方差
    double Var = 0;
    for (int k = 0; k < Grayscale; ++k) {
        if ((MK[Grayscale - 1] * PK[k] - MK[k]) * (MK[Grayscale - 1] * PK[k] - MK[k]) / (PK[k] * (1 - PK[k])) > Var) {
            Var = (MK[Grayscale - 1] * PK[k] - MK[k]) * (MK[Grayscale - 1] * PK[k] - MK[k]) / (PK[k] * (1 - PK[k]));
            thresh = k;
        }
    }

    //阈值处理
    src.copyTo(dst);
    for (int i = 0; i < r; ++i) {
        uchar* ptr = dst.ptr<uchar>(i);
        for (int j = 0; j < c; ++j) {
            if (ptr[j] > thresh)
                ptr[j] = 255;
            else
                ptr[j] = 0;
        }
    }
    return thresh;
}


int main() {
    cv::Mat src = cv::imread("F:\\Pan\\Pictures\\Screenshots\\rhino2.tif");
    if (src.empty()) {
        return -1;
    }
    if (src.channels() > 1)
        cv::cvtColor(src, src, CV_8U);

    cv::Mat dst, dst2;
    int thresh = 0;
    double t2 = (double)cv::getTickCount();
    thresh = Otsu(src, dst, thresh); //Otsu
    std::cout << "Mythresh=" << thresh << std::endl;
    t2 = (double)cv::getTickCount() - t2;
    double time2 = (t2 * 1000.) / ((double)cv::getTickFrequency());
    std::cout << "my_process=" << time2 << " ms. " << std::endl << std::endl;
    double  Otsu = 0;

    Otsu = cv::threshold(src, dst2, Otsu, 255, cv::THRESH_OTSU + cv::THRESH_BINARY);
    std::cout << "OpenCVthresh=" << Otsu << std::endl;

    cv::namedWindow("src", cv::WINDOW_NORMAL);
    cv::imshow("src", src);
    cv::namedWindow("dst", cv::WINDOW_NORMAL);
    cv::imshow("dst", dst);
    cv::namedWindow("dst2", cv::WINDOW_NORMAL);
    cv::imshow("dst2", dst2);
    cv::waitKey(0);
}

尝试了各种：放在同一目录调用，单引号调用，更改图片类型（png），都是报错。恳请大佬帮助。