在opencv中裁剪旋转的图像

Question

Ok so I am having problems cropping my rotated image in opencv. First off does it matter what order the points are in the array fed into minAreaRect? If not then I don't know what is wrong with my code but as soon as I crop the rotated image the cropped image is just a black square. I assume because my box is wrong somehow. Anyway here is my code. Edit: my method was fine the problem is my points for the roi are wrong.

                int len = max(ImageAd.cols, ImageAd.rows);
            cv::Point2f pt(len/2., len/2.);
            cv:: Mat r = cv::getRotationMatrix2D(pt, -angled, 1.0);
            cv::warpAffine(ImageAd, ImageAd, r, ImageAd.size(), INTER_CUBIC);
            vector<cv::Point> points;
            points.push_back(Pt3);
            points.push_back(Pt4);
            points.push_back(Pt1);
            points.push_back(Pt2);

            cv::RotatedRect box = cv::minAreaRect(cv::Mat(points));
            cv::Size box_size = box.size;

            cv::getRectSubPix(ImageAd, box_size, box.center, ImageAd);
            cv::imshow("cropped", ImageAd);

Answer 1

Honestly I never used getRectSubPix so I don't know exactly what is wrong but.. why do just not take a roi? the C++ API with cv::Mat class are very handy for this..

Here is a documentation , you can take a ROI (that is a Region of Interest if you don't know it yet) with the overloaded function call operator of cv::Mat

Anyway here is a snippet for take ROI

cv::Mat img = …;
cv::Mat subImg = img(cv::Rect(0, 0, 100, 100));
cv::Mat subImg = img(cv::Range(0, 0), cv::Range(100, 100));

You have a cv::RotatedRect so you can directly use the RotatedRect::boundingRect property.