One method of scaling, rotating and cropping image by using OpenCV

.cpp

void imageScaleAndRotate(const cv::Mat &src, cv::Mat &out, double scale, double roll) {
    // scaling
		cv::Mat imSmall;
		cv::resize(src, imSmall, cv::Size(), scale, scale);
    
    // prepare for rotating
		int width = imSmall.cols, height = imSmall.rows;
		int diagonal = int(sqrt(height * height + width * width));

		int offsetX = (diagonal - width) / 2, offsetY = (diagonal - height) / 2;
		cv::Mat tmp(diagonal, diagonal, imSmall.type(), cv::Scalar(0, 0, 0, 0));
		imSmall.copyTo(tmp.rowRange(offsetY, offsetY + height).colRange(offsetX, offsetX + width));

    // rotating
		cv::Mat rotated;
		cv::Point2f center(diagonal / 2.0f, diagonal / 2.0f);
		cv::Mat rot_mat = cv::getRotationMatrix2D(center, roll, 1.0f);
		cv::warpAffine(tmp, rotated, rot_mat, tmp.size());
    
    // cropping
		cv::RotatedRect rc(cv::Point2f(width / 2, height / 2), cv::Size2f(width, height), -roll);
		cv::Rect_<float> rcBound = rc.boundingRect2f();
		out = rotated(cv::Rect2f(cv::Point2f(center.x - rcBound.width / 2, center.y - rcBound.height / 2), cv::Size(rcBound.width, rcBound.height)));
	}