PerspectiveTransform PerspectiveTransform::quadrilateralToSquare(float x0, float y0, float x1, float y1, float x2,
float y2, float x3, float y3) {
// Here, the adjoint serves as the inverse:
return squareToQuadrilateral(x0, y0, x1, y1, x2, y2, x3, y3).buildAdjoint();
}
PerspectiveTransform PerspectiveTransform::buildAdjoint() {
// Adjoint is the transpose of the cofactor matrix:
PerspectiveTransform result(PerspectiveTransform(a22 * a33 - a23 * a32, a23 * a31 - a21 * a33, a21 * a32
- a22 * a31, a13 * a32 - a12 * a33, a11 * a33 - a13 * a31, a12 * a31 - a11 * a32, a12 * a23 - a13 * a22,
a13 * a21 - a11 * a23, a11 * a22 - a12 * a21));
return result;
}
PerspectiveTransform PerspectiveTransform::times(PerspectiveTransform other) {
PerspectiveTransform result(PerspectiveTransform(a11 * other.a11 + a21 * other.a12 + a31 * other.a13,
a11 * other.a21 + a21 * other.a22 + a31 * other.a23, a11 * other.a31 + a21 * other.a32 + a31
* other.a33, a12 * other.a11 + a22 * other.a12 + a32 * other.a13, a12 * other.a21 + a22
* other.a22 + a32 * other.a23, a12 * other.a31 + a22 * other.a32 + a32 * other.a33, a13
* other.a11 + a23 * other.a12 + a33 * other.a13, a13 * other.a21 + a23 * other.a22 + a33
* other.a23, a13 * other.a31 + a23 * other.a32 + a33 * other.a33));
return result;
}
void PerspectiveTransform::transformPoints(vector<float> &points) {
int max = points.size();
for (int i = 0; i < max; i += 2) {
float x = points[i];
float y = points[i + 1];
float denominator = a13 * x + a23 * y + a33;
points[i] = (a11 * x + a21 * y + a31) / denominator;
points[i + 1] = (a12 * x + a22 * y + a32) / denominator;
}
}
对一张透视图片变换回正面图的效果:
int main(){
Mat img=imread("boy.png");
int img_height = img.rows;
int img_width = img.cols;
Mat img_trans = Mat::zeros(img_height,img_width,CV_8UC3);
PerspectiveTransform tansform = PerspectiveTransform::quadrilateralToQuadrilateral(
0,0,
img_width-1,0,
0,img_height-1,
img_width-1,img_height-1,
150,250, // top left
771,0, // top right
0,1023,// bottom left
650,1023
);
vector<float> ponits;
for(int i=0;i<img_height;i++){
for(int j=0;j<img_width;j++){
ponits.push_back(j);
ponits.push_back(i);
}
}
tansform.transformPoints(ponits);
for(int i=0;i<img_height;i++){
uchar* t= img_trans.ptr<uchar>(i);
for (int j=0;j<img_width;j++){
int tmp = i*img_width+j;
int x = ponits[tmp*2];
int y = ponits[tmp*2+1];
if(x<0||x>(img_width-1)||y<0||y>(img_height-1))
continue;
uchar* p = img.ptr<uchar>(y);
t[j*3] = p[x*3];
t[j*3+1] = p[x*3+1];
t[j*3+2] = p[x*3+2];
}
}
imwrite("trans.png",img_trans);
return 0;
}