Table of contents

1. GUI interface under OpenCV

OpenCV provides a powerful GUI interface, which can be used under MFC, Qt, WinForms, Cocoa and other platforms.

The new HighGUI interface functions include the following:

Create and control windows for displaying pictures and recording their contents

Added a sliding control bar to the window, which can be easily controlled by mouse and keyboard

The UI interface functions mainly include the following:

createTrackbar

getTracbarPos

setTrackbarPos

imshow

namedWindow

destroyWindow

destroyAllWindows

MoveWindow

ResizeWindow

setMouseCallback

waitKey

(1) Callback function

The callback function refers to the function that is called automatically when an event (such as the sliding of the slider controlled by the slider, mouse operation, keyboard operation, etc.) occurs.

(1) slider control trackbars

createTrackbar(const string &trackbarname,const string&winname,int * value,int count,TrackbarCallback onChange=0,void*userdata=0);
1.trackbarname: 是控件标签
2.winname: 是要添加滑杆控件的窗口名称
3.value: 是存储滑杆位置的变量地址，其范围为0~alpha_slider_max
4.count: 是滑杆的最大值，其最小值为0
5.onChange: 是移动滑杆时调用的回调函数，应具备void Foo(int,void*)的形式，其中，第一个参数为滑块当前的位置，第二个参数为用户的数据
6.userdata: 是需要传递给回调函数的数据。

Some basic operations (instances) of Mat class templates in OpenCV (details about ColorReduce)

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


using namespace cv;
using namespace std;

const int slider_max = 64;
int slider;
Mat image;
Mat result;

void colorReduce(Mat&inputImage,Mat&outputImage,int div){
    outputImage = inputImage.clone();
    int rows = outputImage.rows;
    int cols = outputImage.cols * outputImage.channels();
    if(outputImage.isContinuous()){
        cols = cols * rows;
        rows = 1;
    }
    for(int i = 0; i < rows ; i++){
        uchar*dataout = outputImage.ptr<uchar>(i);
        for(int j = 0; j < cols; j++){
            dataout[j] = dataout[j] / div * div + div / 2;
        }
    }

}

//rackbar事件的回调函数
void on_trackbar(int pos,void*){
    if(pos <= 0){
        result = image;
    }else{
        colorReduce(image,result,pos);
    }
    imshow("result image!",result);
}

int main()
{
    //读取图片
    image = imread("../images/cat.png");

    //创建两个窗口
    namedWindow("Original image!");
    namedWindow("result image!");

    slider = 0;
    createTrackbar("colorReduce","result image!",&slider,slider_max,on_trackbar);

    //显示图像
    imshow("Original image!",image);
    imshow("result image!",image);

    waitKey(0);

    return 0;
}

(2) Mouse operation callback function

setMouseCallback(const string&winname,MouseCallback onMouse,void*,userdata);
1.winname: 表示要添加的回调函数的窗口名称
2.onMouse: 是鼠标操作回调函数，函数原型如下：
            void Foo(int event,int x,int y,int flags,void * param);
            1.event:表示EVENT_*变量之一，
            2.x,y：表示鼠标指针在图像坐标位置（注意不是窗口坐标系）
            3.flags: 表示EVENT_FLAG的组合，
            4.param: 是用户定义的传递到setMouseCallback函数调用的参数
3.userdata：需要传递给回调函数的数据。

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


using namespace cv;
using namespace std;


//鼠标按键标志
bool ldown = false,lup = false;
//原始图像
Mat image;
//矩形起始点和终点坐标
Point corner1,corner2;
//感兴趣区域
Rect box;


//鼠标事件的回调函数

static void mouse_callback(int event,int x,int y,int ,void*){
    //当鼠标左键按下时，记录器状态和坐标

    if(event == EVENT_LBUTTONDOWN){
        ldown = true;
        corner1.x = x;
        corner1.y = y;
        cout<<"Corner1 recorded at" <<corner1<<endl;
    }
    //当鼠标左键放开时，记录器状态和坐标
    if(event == EVENT_LBUTTONUP){
        //判断选取的ROI区域是否大于20个像素
        if(abs(x - corner1.x) > 20 && abs(y - corner1.y) > 20){
            lup = true;
            corner2.x = x;
            corner2.y = y;
            cout<<"Corner2 recorded at" <<corner2<<endl;
        }else{
            cout<<"Please select a bigger region"<<endl;
            ldown = false;
        }
    }

    //当移动鼠标时，更新选择区域，并绘制矩形选择区域图形
    if(ldown == true && lup == false){
        Point pt;
        pt.x = x;
        pt.y = y;
        Mat local_img = image.clone();
        rectangle(local_img,corner1,pt,Scalar(0,0,255));
        imshow("Cropping app",local_img);
    }

    //定义ROI区域，并对原始图像进行裁剪
    if(ldown == true && lup == true){
        box.width = abs(corner1.x - corner2.x);
        box.height = abs(corner1.y - corner2.y);
        box.x = min(corner1.x,corner2.x);
        box.y = min(corner1.y,corner2.y);


        //对原始图像进行裁剪，并生成新的图像
        Mat crop(image,box);
        namedWindow("Crop");
        imshow("Crop",crop);
        ldown = false;
        lup = false;
    }
}


int main()
{
    //读取图片
    image = imread("../images/cat.png");

    //创建两个窗口
    namedWindow("Cropping app");
    imshow("Cropping app",image);

    //设置鼠标事件回调函数
    setMouseCallback("Cropping app",mouse_callback);

    //按下q关闭窗口
    while(char(waitKey(1)) != 'q'){}

    return 0;
}

(3) Keyboard response function

函数原型：
int waiKey(int delay = 0);
1.当delay<=0时，会永久的等待；
2.当delay>0时，表示等待delay毫秒，返回所按下键的扫描码
3.若为按下键，则返回-1.

Graphical interaction and media interface HighGUI under OpenCV

1. GUI interface under OpenCV

(1) Callback function

(1) slider control trackbars

(2) Mouse operation callback function

(3) Keyboard response function

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