学步园

图像旋转矩阵为 T = [ cos(alpha)  sin(alpha); -sin(alpha)  cos(alpha) ],  该矩阵为顺时针旋转alpha角度的矩阵。但图像中原点位于左上角，施加该矩阵得到的是逆时针旋转alpha角度的图像，所以顺时针旋转的变换矩阵为T = [ cos(alpha)  -sin(alpha); sin(alpha)  cos(alpha) ]。

代码如下：

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
#include <cmath>

using namespace cv;
using namespace std;

#define PI 3.14159265


void MyRotation(Mat& src, Mat& dst, float TransMat[3][3]);

/**
 * @function main
 */
int main( int argc, char** argv )
{
  // load image
  char* imageName = "images/Lenna_256.png";

  Mat image;
  image = imread(imageName,1);
  if(!image.data)
  {
	  cout << "No image data" << endl;
	  return -1;
  }

  // show image
  namedWindow("image", CV_WINDOW_AUTOSIZE);
  imshow("image", image);
  
  
  Mat dst;
  float alpha = 36.0*PI/180;
  float transMat[3][3] = { {cos(alpha), -sin(alpha), 0}, {sin(alpha), cos(alpha), 0}, {0, 0, 1} };// !!! counter clockwise transform matrix, for clockwise rotation !!!
  MyRotation(image, dst, transMat);
  
  namedWindow("out_image", CV_WINDOW_AUTOSIZE);
  imshow("out_image", dst);

  //imwrite("Lenna_rotate.jpg", dst);

  waitKey(0);
  return 0;
}





void MyRotation(Mat& src, Mat& dst, float TransMat[3][3])
{
	CV_Assert(src.data);
	CV_Assert(src.depth() != sizeof(uchar));
	
	// calculate margin point of dst image
	float left =  0;
	float right =  0;
	float top =  0;
	float down =  0;

	float x = src.cols * 1.0f;
	float y = 0.0f;
	float u1 = x * TransMat[0][0] + y * TransMat[0][1];
	float v1 = x * TransMat[1][0] + y * TransMat[1][1];
	x = src.cols * 1.0f;
	y = src.rows * 1.0f;
	float u2 = x * TransMat[0][0] + y * TransMat[0][1];
	float v2 = x * TransMat[1][0] + y * TransMat[1][1];
	x = 0.0f;
	y = src.rows * 1.0f;
	float u3 = x * TransMat[0][0] + y * TransMat[0][1];
	float v3 = x * TransMat[1][0] + y * TransMat[1][1];

	left =  min( min( min(0.0f,u1), u2 ), u3);
	right =  max( max( max(0.0f,u1), u2 ), u3);
	top =  min( min( min(0.0f,v1), v2 ), v3);
	down =  max( max( max(0.0f,v1), v2 ), v3);

	// create dst image
	dst.create(int(abs(right-left)), int(abs(down-top)), src.type());
	

	CV_Assert( dst.channels() == src.channels() );
	int channels = dst.channels();

	int i,j;
	uchar* p;
	uchar* q;
	for( i = 0; i < dst.rows; ++i)
	{
		p = dst.ptr<uchar>(i);
		for ( j = 0; j < dst.cols; ++j)
		{
			// rotation
			int x = (j+left)*TransMat[0][0] - (i+top)*TransMat[0][1] ; // NOTE: adverse rotation here!!!
			int y = -(j+left)*TransMat[1][0] + (i+top)*TransMat[1][1] ;


			if( (x >= 0) && (x < src.cols) && (y >= 0) && (y < src.rows) ) 
			{
				q = src.ptr<uchar>(y);
				switch(channels)
				{
					case 1:
						{
							p[j] = q[x];
							break;
						}
					case 3:
						{
							p[3*j] = q[3*x] ;
							p[3*j+1] = q[3*x+1];
							p[3*j+2] = q[3*x+2];
							break;
						}
				}
			}
		}
	}
}