如何从图像遮罩旋转的矩形？

Question

I have an image that I need to mask some portion of it. The portion is a rotated rectangle. When I pass on the arguments of top-left corner and bottom-right corner to the function cv.rectangle() , it does not form a rotated rectangle, instead, it draws a rectangle with no tilt. However, I want to mask a rotated rectangle in an image and I have all the four coordinates of the rectangle. Is there any way to do this? Thank you. Any help is appreciated. I am using OpenCV in python.

Answer 1

To draw a rotated rectangle, extract the four corners into a contour, then use cv::drawContours

cv::RotatedRect rr(cv::Point(x, y), cv::Size(w, h), angle);
cv::Point2f pts[4];
rr.points(pts);
std::vector<std::vector<cv::Point>> contours;
contours.push_back(std::vector<cv::Point>());
for(int i = 0; i < 4; i++) contours[0].push_back(pts[i]);
cv::drawContours(image, contours, 0, cv::Scalar::all(255), -1);

oops, that's C++ ... but transcoding to python should be straightforward :) Section 7 of this tutorial has what you need.