OpenCV (3) OpenCV Drawing and Annotating

1. Draw a circle:

OpenCV provides some functions to make lines, squares, circles on the top of an image.

For example, we can draw a circle on our image.

#include
#include

using namespace std;
using namespace cv;

int main() {
    Mat img = imread("mini.jpg");
    circle(
        img, // draw on the top of this image 
        Point(100, 60),           // center
        60,                       // radius
        Scalar(0x00, 0x00, 0xFF), // color (BGR)
        2                         // thickness
        );

    imshow("Image", img);
    
    waitKey(0);
    destroyAllWindows();

    return 0;
}

2. Annotation:

Furthermore, we can put some text on our image.

#include
#include

using namespace std;
using namespace cv;

int main() {
    Mat img = imread("mini.jpg");
    circle(
        img, 
        Point(100, 60),           // center
        60,                       // radius
        Scalar(0x00, 0x00, 0xFF), // color (BGR)
        2                         // thickness
        );

    putText(
        img,
        String("minion A"),        // annotation
        Point(10, 30),           // position
        FONT_HERSHEY_PLAIN,      // font
        1,                       // font size
        Scalar(0x00, 0x00, 0xFF) // color (BGR)
        );

    imshow("Image", img);
    
    waitKey(0);
    destroyAllWindows();

    return 0;
}

Reference

[1] Adrian Kaehler, Gary Bradski, Learning OpenCV 3 , O'Reilly Media (2017)