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人脸相关应用的重要预处理，very useful!

// find affine transformation between two pointsets (use least square matching)bool computeAffine(const vector
   
     &srcPoints, const vector
    
      &dstPoints, Mat &transf){    // sanity check    if ((srcPoints.size() < 3) || (srcPoints.size() != dstPoints.size()))        return false;    // container for output    transf.create(2, 3, CV_32F);    // fill the matrices    const int n = (int)srcPoints.size(), m = 3;    Mat A(n,m,CV_32F), xc(n,1,CV_32F), yc(n,1,CV_32F);    for(int i=0; i
     
      (i,0) = dstPoints[i].x;        yc.at
      
       (i,0) = dstPoints[i].y;    }    // solve linear equations (for x and for y)    Mat aTa, resX, resY;    mulTransposed(A, aTa, true);    solve(aTa, A.t()*xc, resX, DECOMP_CHOLESKY);    solve(aTa, A.t()*yc, resY, DECOMP_CHOLESKY);    // store result    memcpy(transf.ptr
       
        (0), resX.data, m*sizeof(float));    memcpy(transf.ptr
        
         (1), resY.data, m*sizeof(float)); return true;}int faceAlign(Mat src, Mat &output, vector
         
           pointSrc){ if(!src.data) { cout << "image not read properly" << endl; return -1; } // Dimensions of output image int w = 200; int h = 200; vector
          
            pointDst; pointDst.push_back(Point2f( 64, 100)); //左眼角 pointDst.push_back(Point2f( 136, 100)); //右眼角 pointDst.push_back(Point2f(100,130)); //鼻尖 pointDst.push_back(Point2f(68,150)); //左嘴角 pointDst.push_back(Point2f(132,150)); //右嘴角 // Calculate similarity transform Mat tform; computeAffine(pointSrc, pointDst, tform); // Apply transform to input image Mat AffineImg = Mat::zeros(h, w, CV_32FC3); warpAffine(src, AffineImg, tform, AffineImg.size()); output = AffineImg; imshow("img", AffineImg); //waitKey(); return 1;}
          
         
        
       
      
     
    
   

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