Mat类的构造函数有20多种，详见https://docs.opencv.org/4.1.1/d3/d63/classcv_1_1Mat.html#af1d014cecd1510cdf580bf2ed7e5aafc；
现列出几种常用构造函数以及方法：
1.Mat(int rows,int cols ,int type);
parameters：
| rows | Number of rows in a 2D array. |
| cols | Number of columns in a 2D array. |
| type | Array type. Use CV_8UC1, ..., CV_64FC4 to create 1-4 channel matrices, or CV_8UC(n), ..., CV_64FC(n) to create multi-channel (up to CV_CN_MAX channels) matrices. |
2.Mat(Size size ,int type);
Parameters :
| size | 2D array size: Size(cols, rows) . In the Size() constructor, the number of rows and the number of columns go in the reverse order. |
| type | Array type. Use CV_8UC1, ..., CV_64FC4 to create 1-4 channel matrices, or CV_8UC(n), ..., CV_64FC(n) to create multi-channel (up to CV_CN_MAX channels) matrices. |
3. Mat(int rows,int cols ,int type,const Scalar & s);
Parameters:
| rows | Number of rows in a 2D array. |
| cols | Number of columns in a 2D array. |
| type | Array type. Use CV_8UC1, ..., CV_64FC4 to create 1-4 channel matrices, or CV_8UC(n), ..., CV_64FC(n) to create multi-channel (up to CV_CN_MAX channels) matrices. |
| s | An optional value to initialize each matrix element with. To set all the matrix elements to the particular value after the construction, use the assignment operator Mat::operator=(const Scalar& value) . |
4.Mat(Size size ,int type,const Scalar & s);
Parameters:
| size | 2D array size: Size(cols, rows) . In the Size() constructor, the number of rows and the number of columns go in the reverse order. |
| type | Array type. Use CV_8UC1, ..., CV_64FC4 to create 1-4 channel matrices, or CV_8UC(n), ..., CV_64FC(n) to create multi-channel (up to CV_CN_MAX channels) matrices. |
| s | An optional value to initialize each matrix element with. To set all the matrix elements to the particular value after the construction, use the assignment operator Mat::operator=(const Scalar& value) . |
Mat img;//创建无初始化矩阵
Mat img1(200,100,CV_8UC1);//200行，100列（长200，宽100）
Mat img2(Size(200,100),CV_8UC3,Scalar(0,255,0));//长100，宽200
Mat img3(200,100,CV_8UC3,Scalar(0,255,0));//创建200行，100列的8位三通道矩阵
Mat img4(200,100,CV_8UC1,Scalar(255));//创建单通道矩阵
方法：
参考：https://docs.opencv.org/4.1.1/d3/d63/classcv_1_1Mat.html#a33fd5d125b4c302b0c9aa86980791a77；
Mat img2(img1);
Mat img3 = img1;
Mat img4 = img1.clone();
Mat img5;
img1.copyTo(img5);
// cvtColor(img1, img1, COLOR_BGR2GRAY);
imshow("img1", img1);
imshow("img2", img2);
imshow("img3", img3);//image1/2/3跟随原图变化
imshow("img4", img4);
imshow("img5", img5);//image4/5不会跟随原图变化
waitKey(0);
-
第一个参数，InputOutputArray img，要绘制椭圆的图像；
-
第二个参数，const RotatedRect& box，通过RotatedRect选择椭圆表示，这意味着函数在旋转矩形中画一个椭圆；
-
第三个参数，Point center，椭圆的中心点；
-
第四个参数，Size axes，椭圆主轴尺寸的一半；
-
第五个参数，double angle，椭圆旋转角，以度为单位；
-
第六个参数，double startAngle，椭圆弧的起始角，以度为单位；
-
第七个参数，double endAngle，椭圆弧的结束角，以度为单位；
-
第八个参数，const Scalar& color，绘制椭圆线的颜色；
-
第九个参数，int thickness = 1，线段的粗细；
-
第十个参数，int lineType = LINE_8，线段的类型；
-
线的类型：
FILLED，填充；
LINE_4，4连通的线条；
LINE_8 ，8连通的线条；
LINE_AA ，抗锯齿线条；
imshow("原图", image);
RNG rng = theRNG();
line(image, Point(20, 20), Point(100, 100), Scalar(0,0,0), 5, 8);
Scalar color(rng.uniform(0, 250), rng.uniform(0, 250), rng.uniform(0, 250));
circle(image, Point(60, 60), 60, color, 1, 8);
rectangle(image, Point(20, 20), Point(100, 100), color, 1, 8);
imshow("绘图", image);