CODEWITHSUNDEEP
c++opencv
Adel Khatem
Adel Khatem

Reputation: 319

Draw rectangle in OpenCV

I want to draw a rectangle in OpenCV by using this function:

rectangle(Mat& img, Rect rec, const Scalar& color, int thickness=1, int lineType=8, int shift=0 )

But when I use it I am facing some errors. My question is: can anyone explain the function with an example? I found some examples but with another function: 

rectangle(Mat& img, Point pt1, Point pt2, const Scalar& color, int thickness=1, int lineType=8, int shift=0)

This example on the second function: 

rectangle(image, pt2, pt1, Scalar(0, 255, 0), 2, 8, 0);

This function I understand, but with the first function I'm facing a problem in parameter Rect. I don't know how I can deadlier it?

Upvotes: 20

Views: 96692

Answers (2)

Robert Prévost
Robert Prévost

Reputation: 1717

The cv::rectangle function that accepts two cv::Point's takes both the top left and the bottom right corner of a rectangle (pt1 and pt2 respectively in the documentation). If that rectangle is used with the cv::rectangle function that accepts a cv::Rect, then you will get the same result.

// just some valid rectangle arguments
int x = 0;
int y = 0;
int width = 10;
int height = 20;
// our rectangle...
cv::Rect rect(x, y, width, height);
// and its top left corner...
cv::Point pt1(x, y);
// and its bottom right corner.
cv::Point pt2(x + width, y + height);
// These two calls...
cv::rectangle(img, pt1, pt2, cv::Scalar(0, 255, 0));
// essentially do the same thing
cv::rectangle(img, rect, cv::Scalar(0, 255, 0))

Upvotes: 26

Saransh Kejriwal
Saransh Kejriwal

Reputation: 2533

Here's a simple example of drawing a pre-defined rectangle on an image

using namespace cv;

int main(){
Mat img=imread("myImage.jpg");

Rect r=Rect(10,20,40,60);
//create a Rect with top-left vertex at (10,20), of width 40 and height 60 pixels.

rectangle(img,r,Scalar(255,0,0),1,8,0);
//draw the rect defined by r with line thickness 1 and Blue color

imwrite("myImageWithRect.jpg",img);


return 0;
}

Upvotes: 9

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