问题
I have a cylindrical object on which a circular label is pasted. I extract the contour of the image.
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I know the radius of the cylindrical object as well as the label. But not every time the ellipse obtained will be exactly symmetrical. How can I unwrap the ellipse into a circle?
Here's an image which is not symmetrical
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EDITED I tried to extend @Haris's solution something like this
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Instead of just just 4 points, I want to use an array of points to get a more accurate circle. But getPerspectiveTransform
won't allow me to have more than 4 points. Is there a better way to this?
回答1:
So you want to transform your object to minimum enclosing circle,
Like in the below image transform reed rectangle to green circle. That is transform bounding rectangle to bounding circle.
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So do the following,
Threshold the image
Find contour and calculate bounding rect and minmum enclosing circle for contour.
Mat src=imread("src.png");
Mat thr;
cvtColor(src,thr,CV_BGR2GRAY);
threshold( thr, thr, 20, 255,CV_THRESH_BINARY_INV );
bitwise_not(thr,thr);
vector< vector <Point> > contours; // Vector for storing contour
vector< Vec4i > hierarchy;
Mat dst(src.rows,src.cols,CV_8UC1,Scalar::all(0)); //create destination image
findContours( thr.clone(), contours, hierarchy,CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE ); // Find the contours in the image
drawContours( dst,contours, 0, Scalar(255,255,255),CV_FILLED, 8, hierarchy );
Rect R=boundingRect(contours[0]);
Point2f center;
float radius;
minEnclosingCircle( (Mat)contours[0], center, radius);`
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- Apply warpPerspective
Here you need calculate transformation matrix from bounding box and circle like
std::vector<Point2f> src_pts;
std::vector<Point2f> dst_pts;
src_pts.push_back(Point(R.x,R.y));
src_pts.push_back(Point(R.x+R.width,R.y));
src_pts.push_back(Point(R.x,R.y+R.height));
src_pts.push_back(Point(R.x+R.width,R.y+R.height));
dst_pts.push_back(Point2f(center.x-radius,center.y-radius));
dst_pts.push_back(Point2f(center.x+radius,center.y-radius));
dst_pts.push_back(Point2f(center.x-radius,center.y+radius));
dst_pts.push_back(Point2f(center.x+radius,center.y+radius));
Mat transmtx = getPerspectiveTransform(src_pts,dst_pts);
and then apply perspective transform,
Mat transformed = Mat::zeros(src.rows, src.cols, CV_8UC3);
warpPerspective(src, transformed, transmtx, src.size());
imshow("transformed", transformed);
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来源:https://stackoverflow.com/questions/23240141/unwarp-curved-surface