1. 使用矩形将图像中某个区域置为黑色

推荐参考博客：OpenCV实现将任意形状ROI区域置黑（多边形区域置黑）

比较常用的是使用 Rect 矩形实现该功能，代码如下：

#include <opencv2\opencv.hpp>int main() {std::string filePath = "img.png";cv::Mat img = cv::imread(filePath);//创建矩形int x = img.cols / 2;    // x 对应列坐标int y = img.rows / 2;    // y 对应行坐标int width = 150;int height = 80;cv::Rect rect(x, y, width, height);//将矩形贴到img中，并将矩形区域置为黑色cv::Mat subImg = img(rect);subImg.setTo(0);cv::imwrite("img_rect.png", img);return 0;
}

效果如下：

2. cv::Rect 类介绍

推荐参考博客：OpenCV 中 cv::Rect 矩形类用法

cv::Rect 用于创建矩形，API 参数如下：

int x;    // 左上角 x 坐标，对应列坐标
int y;    // 左上角 y 坐标，对应列坐标
int width;     // 宽
int height;    // 高

源码如下：

template<typename _Tp> class Rect_
{
public:typedef _Tp value_type;//! default constructorRect_();Rect_(_Tp _x, _Tp _y, _Tp _width, _Tp _height);Rect_(const Rect_& r);Rect_(Rect_&& r) CV_NOEXCEPT;Rect_(const Point_<_Tp>& org, const Size_<_Tp>& sz);Rect_(const Point_<_Tp>& pt1, const Point_<_Tp>& pt2);Rect_& operator = ( const Rect_& r );Rect_& operator = ( Rect_&& r ) CV_NOEXCEPT;//! the top-left cornerPoint_<_Tp> tl() const;//! the bottom-right cornerPoint_<_Tp> br() const;//! size (width, height) of the rectangleSize_<_Tp> size() const;//! area (width*height) of the rectangle_Tp area() const;//! true if emptybool empty() const;//! conversion to another data typetemplate<typename _Tp2> operator Rect_<_Tp2>() const;//! checks whether the rectangle contains the pointbool contains(const Point_<_Tp>& pt) const;_Tp x; //!< x coordinate of the top-left corner_Tp y; //!< y coordinate of the top-left corner_Tp width; //!< width of the rectangle_Tp height; //!< height of the rectangle
};typedef Rect_<int> Rect2i;
typedef Rect_<float> Rect2f;
typedef Rect_<double> Rect2d;
typedef Rect2i Rect;