图像旋转算法的实现

上一篇转载的文章（http://blog.csdn.net/carson2005/article/details/36900161）介绍了图像旋转的原理，这里给出代码实现，具体原理请参考上面的链接；

实现代码：

void ImgRotate(cv::Mat imgIn, float theta, cv::Mat& imgOut)
{
	int oldWidth = imgIn.cols;
	int oldHeight = imgIn.rows;

	// 源图四个角的坐标（以图像中心为坐标系原点）
	float fSrcX1,fSrcY1,fSrcX2,fSrcY2,fSrcX3,fSrcY3,fSrcX4,fSrcY4;
	fSrcX1 = (float) (- (oldWidth  - 1) / 2);
	fSrcY1 = (float) (  (oldHeight - 1) / 2);
	fSrcX2 = (float) (  (oldWidth  - 1) / 2);
	fSrcY2 = (float) (  (oldHeight - 1) / 2);
	fSrcX3 = (float) (- (oldWidth  - 1) / 2);
	fSrcY3 = (float) (- (oldHeight - 1) / 2);
	fSrcX4 = (float) (  (oldWidth  - 1) / 2);
	fSrcY4 = (float) (- (oldHeight - 1) / 2);

	// 旋转后四个角的坐标（以图像中心为坐标系原点）
	float fDstX1,fDstY1,fDstX2,fDstY2,fDstX3,fDstY3,fDstX4,fDstY4;
	fDstX1 =  cos(theta) * fSrcX1 + sin(theta) * fSrcY1;
	fDstY1 = -sin(theta) * fSrcX1 + cos(theta) * fSrcY1;
	fDstX2 =  cos(theta) * fSrcX2 + sin(theta) * fSrcY2;
	fDstY2 = -sin(theta) * fSrcX2 + cos(theta) * fSrcY2;
	fDstX3 =  cos(theta) * fSrcX3 + sin(theta) * fSrcY3;
	fDstY3 = -sin(theta) * fSrcX3 + cos(theta) * fSrcY3;
	fDstX4 =  cos(theta) * fSrcX4 + sin(theta) * fSrcY4;
	fDstY4 = -sin(theta) * fSrcX4 + cos(theta) * fSrcY4;

	int newWidth  = ( max( fabs(fDstX4 - fDstX1), fabs(fDstX3 - fDstX2) ) + 0.5);
	int newHeight = ( max( fabs(fDstY4 - fDstY1), fabs(fDstY3 - fDstY2) )  + 0.5);

	imgOut.create(newHeight, newWidth, imgIn.type());

	float dx = -0.5*newWidth*cos(theta) - 0.5*newHeight*sin(theta) + 0.5*oldWidth;
	float dy = 0.5*newWidth*sin(theta) - 0.5*newHeight*cos(theta) + 0.5*oldHeight;

	int x,y;
	for (int i=0; i<newHeight; i++)
	{
		for (int j=0; j<newWidth; j++)
		{
			x = float(j)*cos(theta) + float(i)*sin(theta) + dx;
			y = float(-j)*sin(theta) + float(i)*cos(theta) + dy;

			if ((x<0) || (x>=oldWidth) || (y<0) || (y>=oldHeight))
			{
				if (imgIn.channels() == 3)
				{
					imgOut.at<cv::Vec3b>(i,j) = cv::Vec3b(0,0,0);
				}
				else if (imgIn.channels() == 1)
				{
					imgOut.at<uchar>(i,j) = 0;
				}
			}
			else
			{
				if (imgIn.channels() == 3)
				{
					imgOut.at<cv::Vec3b>(i,j) = imgIn.at<cv::Vec3b>(y,x);
				}
				else if (imgIn.channels() == 1)
				{
					imgOut.at<uchar>(i,j) = imgIn.at<uchar>(y,x);
				}
			}
		}
	}
}

测试代码：

void ImgRotateTest()
{
	cv::Mat srcImg = cv::imread("test.jpg");
	if (srcImg.empty())
	{
		printf("srcImg load error \n");
		system("pause");
		exit(-1);
	}

	float angle = 30.0f*3.1415926/180.0f;

	cv::Mat dstImg;
	ImgRotate(srcImg, angle, dstImg);
	cv::imwrite("result.jpg", dstImg);
	cv::imshow("src", srcImg);
	cv::imshow("dst", dstImg);
	cv::waitKey(0);

}

测试结果：