adaptiveThreshold(~gray_src, binImg, 255, ADAPTIVE_THRESH_MEAN_C, THRESH_BINARY, 15, -2);

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
int main(int argc, char** argv) {
    Mat src, dst;
    src = imread("E:/opencv3.2/TestOpenCVInstall/Debug/chars.png");
    if (!src.data) {
        printf("could not load image...\n");
        return -1;
    }

    char INPUT_WIN[] = "input image";
    char OUTPUT_WIN[] = "result image";
    namedWindow(INPUT_WIN, CV_WINDOW_AUTOSIZE);
    imshow(INPUT_WIN, src);

    Mat gray_src;
    cvtColor(src, gray_src, CV_BGR2GRAY);
    imshow("gray image", gray_src);
    
    Mat binImg;
    adaptiveThreshold(~gray_src, binImg, 255, ADAPTIVE_THRESH_MEAN_C, THRESH_BINARY, 15, -2);
    imshow("binary image", binImg);

    // 水平结构元素
    Mat hline = getStructuringElement(MORPH_RECT, Size(src.cols / 16, 1), Point(-1, -1));
    // 垂直结构元素
    Mat vline = getStructuringElement(MORPH_RECT, Size(1, src.rows / 16), Point(-1, -1));
    // 矩形结构
    Mat kernel = getStructuringElement(MORPH_RECT, Size(3, 3), Point(-1, -1));

    Mat temp;
    erode(binImg, temp, kernel);
    dilate(temp, dst, kernel);
    // morphologyEx(binImg, dst, CV_MOP_OPEN, vline);
    bitwise_not(dst, dst);
    //blur(dst, dst, Size(3, 3), Point(-1, -1));
    imshow("Final Result", dst);

    waitKey(0);
    return 0;
}