学习OpenCV3：warpAffine旋转图片，鼠标操作截图

太过爱你忘了你带给我的痛 2023-02-18 06:28 22阅读 0赞

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# 1、背景 #

现有如下一张图片，发现其图案与图片并不平行，故希望先通过滑动条旋转图片角度使图案水平，再将旋转好后的图片截图保存下来。

测试图片：

![format_png_pic_center][]

# 2、实现 #

**初始版本：实现图片旋转功能。**  
缺陷：旋转时超出图片大小的部分无法显示。

#include <opencv2/opencv.hpp>
    #include <iostream>
    #include <string>
    #include <cmath>
    
    // 全局变量
    cv::Mat g_image_original, g_image_result; // 原始图片，处理后的图片
    
    // 滑动条回调函数
    void trackbar_callback(int angle, void *)
    {
        // 旋转中心，旋转角度，缩放比例
        cv::Mat img = cv::getRotationMatrix2D(cv::Point2f(g_image_original.cols * 0.5f, g_image_original.rows * 0.5f), angle, 1);
        // 旋转图片
        warpAffine(g_image_original, g_image_result, img, g_image_original.size());
    }
    
    int main()
    {
        const std::string window_name = "image";
        const std::string path = "E:/VSCode/git/my_program/image/5_1.PNG";
        cv::namedWindow(window_name, cv::WINDOW_AUTOSIZE);
        g_image_original = cv::imread(path);
        if (g_image_original.empty())
        {
            std::cout << "can not open image!" << std::endl;
            return -1;
        }
        // 进度条
        int angle = 0; // 图片旋转的角度
        cv::createTrackbar("angle", window_name, &angle, 360, trackbar_callback);
        while (true)
        {
            trackbar_callback(angle, 0); // 进度条回调函数
            cv::imshow(window_name, g_image_result);
            if (cv::waitKey(10) >= 0)
                break;
        }
        cv::destroyAllWindows();
        return 0;
    }

旋转前：

![format_png_pic_center 1][]

旋转后：

![format_png_pic_center 2][]

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**中间版本：解决图片旋转后无法全部显示的问题。**  
实现方法：旋转前，放大图片使其大小足以容纳原图旋转。旋转时，将已放大的图片缩小至原大小。  
缺陷：无参照物以确保图案平行。

#include <opencv2/opencv.hpp>
    #include <iostream>
    #include <string>
    #include <cmath>
    
    // 全局变量
    cv::Mat g_image_original, g_image_result; // 原始图片，处理后的图片
    
    // 滑动条回调函数
    void trackbar_callback(int angle, void *enlarge)
    {
        double m = *(double *)enlarge;
        // 旋转中心，旋转角度，缩放比例
        cv::Mat img = cv::getRotationMatrix2D(cv::Point2f(g_image_original.cols * 0.5f, g_image_original.rows * 0.5f), angle, 1 / m); // 缩小图片
        // 旋转图片
        warpAffine(g_image_original, g_image_result, img, g_image_original.size());
    }
    
    int main()
    {
        const std::string window_name = "image";
        const std::string path = "E:/VSCode/git/my_program/image/5_1.PNG";
        cv::namedWindow(window_name, cv::WINDOW_AUTOSIZE);
        g_image_original = cv::imread(path);
        if (g_image_original.empty())
        {
            std::cout << "can not open image!" << std::endl;
            return -1;
        }
        // 放大图片
        double m1 = std::sqrt(std::pow(g_image_original.cols, 2) + std::pow(g_image_original.rows, 2)); //计算对角线长度
        double m2 = g_image_original.cols > g_image_original.rows ? g_image_original.rows : g_image_original.cols;
        double m = m1 / m2; // 放大比例
        cv::resize(g_image_original, g_image_original, cv::Size(g_image_original.cols * m, g_image_original.rows * m));
        // 进度条
        int angle = 0; // 图片旋转的角度
        cv::createTrackbar("angle", window_name, &angle, 360, trackbar_callback, &m);
        while (true)
        {
            trackbar_callback(angle, &m); // 进度条回调函数
            cv::imshow(window_name, g_image_result);
            if (cv::waitKey(10) >= 0)
                break;
        }
        cv::destroyAllWindows();
        return 0;
    }

旋转前：

![format_png_pic_center 3][]

旋转后：

![format_png_pic_center 4][]

--------------------

**最终版本：通过鼠标调整4条直线使其分布在图案四周，方便确定图案已平行，同时也可用于截取图案。**  
操作方法：首先按下鼠标左键选择任意一条绿线，然后一直按住左键移动鼠标使绿线接近图案。同样方法移动其它3条绿线，使其包围住图案。通过滑动条旋转角度使图案与绿线平行，按`s`键保存4条绿线包围的矩形图片。

#include <opencv2/opencv.hpp>
    #include <iostream>
    #include <string>
    #include <cmath>
    
    // 全局变量
    cv::Mat g_image_original, g_image_result; // 原始图片，处理后的图片
    cv::Rect g_image_xywh;                    // 可通过鼠标移动由4条直线组成的矩形
    
    // 画4条直线
    void draw_lines(cv::Mat img, cv::Rect rect)
    {
        cv::Scalar color(0, 255, 0); // 颜色
        int thickness = 2;           // 厚度
        // 按顺时针画4条线
        cv::line(img, cv::Point(0, rect.y), cv::Point(img.cols, rect.y), color, thickness);                             // 上边
        cv::line(img, cv::Point(rect.x + rect.width, 0), cv::Point(rect.x + rect.width, img.rows), color, thickness);   // 右边
        cv::line(img, cv::Point(0, rect.y + rect.height), cv::Point(img.cols, rect.y + rect.height), color, thickness); // 下边
        cv::line(img, cv::Point(rect.x, 0), cv::Point(rect.x, img.rows), color, thickness);                             // 左边
    }
    
    // 滑动条的回调函数，用于旋转图片
    void trackbar_callback(int angle, void *enlarge)
    {
        double m = *(double *)enlarge;
        // 旋转中心，旋转角度，缩放比例
        cv::Mat img = cv::getRotationMatrix2D(cv::Point2f(g_image_original.cols * 0.5f, g_image_original.rows * 0.5f), angle, 1 / m); // 缩小图片
        // 旋转图片
        warpAffine(g_image_original, g_image_result, img, g_image_original.size());
        // 画4条直线
        draw_lines(g_image_result, g_image_xywh);
    }
    
    // 确定鼠标所点击在那一条线上
    int mouse_location(cv::Rect rect, cv::Point p)
    {
        static int n = 10;
        if (p.y > rect.y - n && p.y < rect.y + n) //上边
            return 1;
        else if (p.x > rect.x + rect.width - n && p.x < rect.x + rect.width + n) //右边
            return 2;
        else if (p.y > rect.y + rect.height - n && p.y < rect.y + rect.height + n) //下边
            return 3;
        else if (p.x > rect.x - n && p.x < rect.x + n) //左边
            return 4;
        else
            return -1;
    }
    
    // 矫正坐标
    void correct(int &m, int n1, int n2)
    {
        if (m < n1)
            m = n1;
        else if (m > n2)
            m = n2;
    }
    
    // 鼠标事件的回调函数，用于移动4条直线以判断图片是否平行，按's'键截取图片并保存
    void mouse_callback(int event, int x, int y, int flags, void *param)
    {
        static cv::Rect rect(0, 0, 0, 0);    // 暂存g_image_xywh
        static cv::Point p1(0, 0), p2(0, 0); // 鼠标左键点击的点、鼠标按住左键移动的点
        static int location = -1;            // 鼠标左键点击落在那条直线上
        cv::Size size(0, 0);                 // 鼠标移动距离
        switch (event)
        {
        case cv::EVENT_LBUTTONDOWN: // 鼠标左键点击
            rect = g_image_xywh;
            p1 = cv::Point(x, y);
            location = mouse_location(g_image_xywh, p1);
            break;
        case cv::EVENT_MOUSEMOVE: // 鼠标移动
            p2 = cv::Point(x, y);
            size = cv::Size(p2.x - p1.x, p2.y - p1.y);
            if (location == 1) //上边
            {
                g_image_xywh.y = rect.y + size.height;
                correct(g_image_xywh.y, 0, g_image_result.rows); // 矫正坐标
                g_image_xywh.height = rect.y + rect.height - g_image_xywh.y;
            }
            else if (location == 2) //右边
            {
                g_image_xywh.width = rect.width + size.width;
                correct(g_image_xywh.width, g_image_xywh.width < -rect.x, g_image_result.cols - rect.x); // 矫正坐标
            }
            else if (location == 3) //下边
            {
                g_image_xywh.height = rect.height + size.height;
                correct(g_image_xywh.height, -rect.y, g_image_result.rows - rect.y); // 矫正坐标
            }
            else if (location == 4) //左边
            {
                g_image_xywh.x = rect.x + size.width;
                correct(g_image_xywh.x, 0, g_image_result.cols); // 矫正坐标
                g_image_xywh.width = rect.x + rect.width - g_image_xywh.x;
            }
            draw_lines(g_image_result, g_image_xywh);
            break;
        case cv::EVENT_LBUTTONUP: // 鼠标左键释放
            rect = cv::Rect(0, 0, 0, 0);
            p1 = cv::Point(0, 0);
            p2 = cv::Point(0, 0);
            location = -1;
            break;
        default:
            break;
        }
    }
    
    int main()
    {
        const std::string window_name = "image";
        const std::string path = "E:/VSCode/git/my_program/image/5_1.PNG";
        int angle = 0; //图片旋转的角度
        g_image_original = cv::imread(path);
        if (g_image_original.empty())
        {
            std::cout << "can not open image!" << std::endl;
            return -1;
        }
        cv::namedWindow(window_name, cv::WINDOW_AUTOSIZE);
    
        // 初始化g_image_xywh
        g_image_xywh.width = g_image_original.cols;
        g_image_xywh.height = g_image_original.rows;
    
        //放大图片，以确保旋转图片时图片保持放大前的尺寸
        double m1 = std::sqrt(std::pow(g_image_original.cols, 2) + std::pow(g_image_original.rows, 2)); //计算对角线长度
        double m2 = g_image_original.cols > g_image_original.rows ? g_image_original.rows : g_image_original.cols;
        double m = m1 / m2; // 放大比例
        cv::resize(g_image_original, g_image_original, cv::Size(g_image_original.cols * m, g_image_original.rows * m));
    
        // 初始化g_image_xywh
        g_image_xywh.x = (g_image_original.cols - g_image_xywh.width) / 2;
        g_image_xywh.y = (g_image_original.rows - g_image_xywh.height) / 2;
    
        //鼠标回调函数
        cv::setMouseCallback(window_name, mouse_callback);
        // 进度条回调函数
        cv::createTrackbar("   angle:", window_name, &angle, 180, trackbar_callback, &m);
        while (true)
        {
            trackbar_callback(angle, &m);
            cv::imshow(window_name, g_image_result);
            char c = cv::waitKey(10);
            if (c == 's') // 按's'保存图片
            {
                int x1 = g_image_xywh.width > 0 ? g_image_xywh.x : g_image_xywh.x + g_image_xywh.width;
                int y1 = g_image_xywh.height > 0 ? g_image_xywh.y : g_image_xywh.y + g_image_xywh.height;
                int thickness = 2; // 由于在图片上画线，截取时需减去线的厚度
                cv::Rect rect(x1 + thickness, y1 + thickness, abs(g_image_xywh.width) - 2 * thickness, abs(g_image_xywh.height) - 2 * thickness);
                cv::imwrite("1.png", g_image_result(rect));
            }
            else if (c > 0 && c != 's') // 按除's'外的键以退出循环
                break;
        }
        cv::destroyAllWindows();
        return 0;
    }

旋转前：

![format_png_pic_center 5][]

旋转后：

![format_png_pic_center 6][]

截取的图片：

![format_png_pic_center 7][]

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