OpenCV实时显示滑动条当前数值

Question

OpenCV C++创建滑动条后，如何显示滑动条的当前数值？
如下，我写了个Canny边缘检测的程序，依靠滑动条来调整低阈值和高阈值，请问怎样才能显示当前的阈值是多少呢？

Mat object = imread("D:\\object.jpg");
int high_thresh, low_thresh;

void call_thresh(int, void*)
{
    resize(object, object, Size(480, 720));

    Mat canny;
    Canny(object, canny, low_thresh, high_thresh);

    Mat contour;

    imshow("边缘", canny);

    waitKey();
}

void find_contour()
{
    namedWindow("边缘");
    createTrackbar("低阈值", "边缘", &low_thresh, 255, call_thresh, 0);
    createTrackbar("高阈值", "边缘", &high_thresh, 255, call_thresh, 0);
    call_thresh(0, 0);
}

Answer 1

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为了实现实时显示滑动条当前数值，你可以在call_thresh函数中通过putText函数将当前阈值显示在图像上。具体实现如下：

#include <opencv2/opencv.hpp>
using namespace cv;

Mat object = imread("D:\\object.jpg");
int high_thresh, low_thresh;

void call_thresh(int, void*)
{
    resize(object, object, Size(480, 720));

    Mat canny;
    Canny(object, canny, low_thresh, high_thresh);

    // 将当前阈值显示在图像上
    std::string low_thresh_str = "低阈值: " + std::to_string(low_thresh);
    std::string high_thresh_str = "高阈值: " + std::to_string(high_thresh);
    putText(canny, low_thresh_str, Point(20, 20), FONT_HERSHEY_SIMPLEX, 0.7, Scalar(255, 255, 255));
    putText(canny, high_thresh_str, Point(20, 50), FONT_HERSHEY_SIMPLEX, 0.7, Scalar(255, 255, 255));

    imshow("边缘", canny);
    waitKey(1);  // 加入适当的延时，以保持实时显示
}

void find_contour()
{
    namedWindow("边缘");
    createTrackbar("低阈值", "边缘", &low_thresh, 255, call_thresh, 0);
    createTrackbar("高阈值", "边缘", &high_thresh, 255, call_thresh, 0);
    call_thresh(0, 0);
}

**注意：**上面代码中的putText函数用于将文本显示在图像上，其中的参数可以根据需要进行调整。此外，为了实现实时显示滑动条当前数值，需要将waitKey函数的参数调整为一个适当的延时时间。你可以根据实际情况进行调整，比如1毫秒（waitKey(1)）。

这样，你就可以在窗口显示的边缘图像上看到当前的低阈值和高阈值了。