env/opencv-4.8.0/samples/cpp/tutorial_code/ImgProc/Threshold.cpp

/**
 * @file Threshold.cpp
 * @brief Sample code that shows how to use the diverse threshold options offered by OpenCV
 * @author OpenCV team
 */

#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>

using namespace cv;
using std::cout;

/// Global variables

int threshold_value = 0;
int threshold_type = 3;
int const max_value = 255;
int const max_type = 4;
int const max_binary_value = 255;

Mat src, src_gray, dst;
const char* window_name = "Threshold Demo";

const char* trackbar_type = "Type: \n 0: Binary \n 1: Binary Inverted \n 2: Truncate \n 3: To Zero \n 4: To Zero Inverted";
const char* trackbar_value = "Value";

//![Threshold_Demo]
/**
 * @function Threshold_Demo
 */
static void Threshold_Demo( int, void* )
{
    /* 0: Binary
     1: Binary Inverted
     2: Threshold Truncated
     3: Threshold to Zero
     4: Threshold to Zero Inverted
    */
    threshold( src_gray, dst, threshold_value, max_binary_value, threshold_type );
    imshow( window_name, dst );
}
//![Threshold_Demo]

/**
 * @function main
 */
int main( int argc, char** argv )
{
    //! [load]
    String imageName("stuff.jpg"); // by default
    if (argc > 1)
    {
        imageName = argv[1];
    }
    src = imread( samples::findFile( imageName ), IMREAD_COLOR ); // Load an image

    if (src.empty())
    {
        cout << "Cannot read the image: " << imageName << std::endl;
        return -1;
    }

    cvtColor( src, src_gray, COLOR_BGR2GRAY ); // Convert the image to Gray
    //! [load]

    //! [window]
    namedWindow( window_name, WINDOW_AUTOSIZE ); // Create a window to display results
    //! [window]

    //! [trackbar]
    createTrackbar( trackbar_type,
                    window_name, &threshold_type,
                    max_type, Threshold_Demo ); // Create a Trackbar to choose type of Threshold

    createTrackbar( trackbar_value,
                    window_name, &threshold_value,
                    max_value, Threshold_Demo ); // Create a Trackbar to choose Threshold value
    //! [trackbar]

    Threshold_Demo( 0, 0 ); // Call the function to initialize

    /// Wait until the user finishes the program
    waitKey();
    return 0;
}