private MatOfPoint OrderCornerPoints(MatOfPoint corners)
{
if (corners.size().area() <= 0 || corners.rows() < 4)
{
return(corners);
}
// rearrange the points in the order of upper left, upper right, lower right, lower left.
using (Mat x = new Mat(corners.size(), CvType.CV_32SC1))
using (Mat y = new Mat(corners.size(), CvType.CV_32SC1))
using (Mat d = new Mat(corners.size(), CvType.CV_32SC1))
using (Mat dst = new Mat(corners.size(), CvType.CV_32SC2))
{
Core.extractChannel(corners, x, 0);
Core.extractChannel(corners, y, 1);
// the sum of the upper left points is the smallest and the sum of the lower right points is the largest.
Core.add(x, y, d);
Core.MinMaxLocResult result = Core.minMaxLoc(d);
dst.put(0, 0, corners.get((int)result.minLoc.y, 0));
dst.put(2, 0, corners.get((int)result.maxLoc.y, 0));
// the difference in the upper right point is the smallest, and the difference in the lower left is the largest.
Core.subtract(y, x, d);
result = Core.minMaxLoc(d);
dst.put(1, 0, corners.get((int)result.minLoc.y, 0));
dst.put(3, 0, corners.get((int)result.maxLoc.y, 0));
dst.copyTo(corners);
}
return(corners);
}
private int CompareContourRows(MatOfPoint mp1, MatOfPoint mp2)
{
int rows1 = mp1.rows();
int rows2 = mp2.rows();
if (rows1 == rows2) { return 0; }
else if (rows1 > rows2) { return -1; }
else { return 1; }
}
private Mat PerspectiveTransform(Mat image, MatOfPoint corners)
{
if (corners.size().area() <= 0 || corners.rows() < 4)
{
return(image);
}
Point[] pts = corners.toArray();
Point tl = pts[0];
Point tr = pts[1];
Point br = pts[2];
Point bl = pts[3];
double widthA = Math.Sqrt((br.x - bl.x) * (br.x - bl.x) + (br.y - bl.y) * (br.y - bl.y));
double widthB = Math.Sqrt((tr.x - tl.x) * (tr.x - tl.x) + (tr.y - tl.y) * (tr.y - tl.y));
int maxWidth = Math.Max((int)widthA, (int)widthB);
double heightA = Math.Sqrt((tr.x - br.x) * (tr.x - br.x) + (tr.y - br.y) * (tr.y - br.y));
double heightB = Math.Sqrt((tl.x - bl.x) * (tl.x - bl.x) + (tl.y - bl.y) * (tl.y - bl.y));
int maxHeight = Math.Max((int)heightA, (int)heightB);
maxWidth = (maxWidth < 1) ? 1 : maxWidth;
maxHeight = (maxHeight < 1) ? 1 : maxHeight;
Mat src = new Mat();
corners.convertTo(src, CvType.CV_32FC2);
Mat dst = new Mat(4, 1, CvType.CV_32FC2);
dst.put(0, 0, 0, 0, maxWidth - 1, 0, maxWidth - 1, maxHeight - 1, 0, maxHeight - 1);
// compute and apply the perspective transformation matrix.
Mat outputMat = new Mat(maxHeight, maxWidth, image.type(), new Scalar(0, 0, 0, 255));
Mat perspectiveTransform = Imgproc.getPerspectiveTransform(src, dst);
Imgproc.warpPerspective(image, outputMat, perspectiveTransform, new Size(outputMat.cols(), outputMat.rows()));
// return the transformed image.
return(outputMat);
}