仿射变换（给定一组三个点前和后的变换，获得变换矩阵）

#include "stdafx.h"
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;
using namespace std;

int main(int argc, char **argv)
{
 // (1)load a specified file as a 3-channel color image
 const string imagename = argc > 1 ? argv[1] : "../image/fruits.jpg";
 Mat src_img = imread(imagename);
 if(!src_img.data)
  return -1;
 // (2)setting three points before and after transformation,
 //    an affine transformation matrix was calculated by getAffineTransform
 const Point2f src_pt[] = { Point2f(200.0, 200.0), Point2f(250.0, 200.0), Point2f(200.0, 100.0) };
 const Point2f dst_pt[] = { Point2f(300.0, 100.0), Point2f(300.0, 50.0), Point2f(200.0, 100.0) };
 const Mat affine_matrix = getAffineTransform(src_pt, dst_pt);
 // (3)rotate the image by warpAffine taking the affine matrix
 Mat dst_img;
 warpAffine(src_img, dst_img, affine_matrix, src_img.size());
 // (4)show source and destination image with two triangles representing the transformation
 line(src_img, src_pt[0], src_pt[1], Scalar(255,255,0), 2);
 line(src_img, src_pt[1], src_pt[2], Scalar(255,255,0), 2);
 line(src_img, src_pt[2], src_pt[0], Scalar(255,255,0), 2);
 line(src_img, dst_pt[0], dst_pt[1], Scalar(255,0,255), 2);
 line(src_img, dst_pt[1], dst_pt[2], Scalar(255,0,255), 2);
 line(src_img, dst_pt[2], dst_pt[0], Scalar(255,0,255), 2);
 namedWindow("src", CV_WINDOW_AUTOSIZE);
 namedWindow("dst", CV_WINDOW_AUTOSIZE);
 imshow("src", src_img);
 imshow("dst", dst_img);
 waitKey(0);
 return 0; 
}

运行结果：