Added quad-segmentation.cpp

1 files changed, 138 insertions, 0 deletions

diff --git a/quad-segmentation.cpp b/quad-segmentation.cpp
new file mode 100644
index 0000000..bb341cd
--- /dev/null
+++ b/quad-segmentation.cpp
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+/**
+ * Automatic perspective correction for quadrilateral objects. See the tutorial at
+ * http://opencv-code.com/tutorials/automatic-perspective-correction-for-quadrilateral-objects/
+ */
+#include <opencv2/imgproc/imgproc.hpp>
+#include <opencv2/highgui/highgui.hpp>
+#include <iostream>
+
+cv::Point2f center(0,0);
+
+cv::Point2f computeIntersect(cv::Vec4i a, 
+                             cv::Vec4i b)
+{
+	int x1 = a[0], y1 = a[1], x2 = a[2], y2 = a[3], x3 = b[0], y3 = b[1], x4 = b[2], y4 = b[3];
+	float denom;
+
+	if (float d = ((float)(x1 - x2) * (y3 - y4)) - ((y1 - y2) * (x3 - x4)))
+	{
+		cv::Point2f pt;
+		pt.x = ((x1 * y2 - y1 * x2) * (x3 - x4) - (x1 - x2) * (x3 * y4 - y3 * x4)) / d;
+		pt.y = ((x1 * y2 - y1 * x2) * (y3 - y4) - (y1 - y2) * (x3 * y4 - y3 * x4)) / d;
+		return pt;
+	}
+	else
+		return cv::Point2f(-1, -1);
+}
+
+void sortCorners(std::vector<cv::Point2f>& corners, 
+                 cv::Point2f center)
+{
+	std::vector<cv::Point2f> top, bot;
+
+	for (int i = 0; i < corners.size(); i++)
+	{
+		if (corners[i].y < center.y)
+			top.push_back(corners[i]);
+		else
+			bot.push_back(corners[i]);
+	}
+
+	cv::Point2f tl = top[0].x > top[1].x ? top[1] : top[0];
+	cv::Point2f tr = top[0].x > top[1].x ? top[0] : top[1];
+	cv::Point2f bl = bot[0].x > bot[1].x ? bot[1] : bot[0];
+	cv::Point2f br = bot[0].x > bot[1].x ? bot[0] : bot[1];
+
+	corners.clear();
+	corners.push_back(tl);
+	corners.push_back(tr);
+	corners.push_back(br);
+	corners.push_back(bl);
+}
+
+int main()
+{
+	cv::Mat src = cv::imread("image.jpg");
+	if (src.empty())
+		return -1;
+
+	cv::Mat bw;
+	cv::cvtColor(src, bw, CV_BGR2GRAY);
+	cv::blur(bw, bw, cv::Size(3, 3));
+	cv::Canny(bw, bw, 100, 100, 3);
+
+	std::vector<cv::Vec4i> lines;
+	cv::HoughLinesP(bw, lines, 1, CV_PI/180, 70, 30, 10);
+
+	// Expand the lines
+	for (int i = 0; i < lines.size(); i++)
+	{
+		cv::Vec4i v = lines[i];
+		lines[i][0] = 0;
+		lines[i][1] = ((float)v[1] - v[3]) / (v[0] - v[2]) * -v[0] + v[1]; 
+		lines[i][2] = src.cols; 
+		lines[i][3] = ((float)v[1] - v[3]) / (v[0] - v[2]) * (src.cols - v[2]) + v[3];
+	}
+	
+	std::vector<cv::Point2f> corners;
+	for (int i = 0; i < lines.size(); i++)
+	{
+		for (int j = i+1; j < lines.size(); j++)
+		{
+			cv::Point2f pt = computeIntersect(lines[i], lines[j]);
+			if (pt.x >= 0 && pt.y >= 0)
+				corners.push_back(pt);
+		}
+	}
+
+	std::vector<cv::Point2f> approx;
+	cv::approxPolyDP(cv::Mat(corners), approx, cv::arcLength(cv::Mat(corners), true) * 0.02, true);
+
+	if (approx.size() != 4)
+	{
+		std::cout << "The object is not quadrilateral!" << std::endl;
+		return -1;
+	}
+
+	// Get mass center
+	for (int i = 0; i < corners.size(); i++)
+		center += corners[i];
+	center *= (1. / corners.size());
+
+	sortCorners(corners, center);
+
+	cv::Mat dst = src.clone();
+
+	// Draw lines
+	for (int i = 0; i < lines.size(); i++)
+	{
+		cv::Vec4i v = lines[i];
+		cv::line(dst, cv::Point(v[0], v[1]), cv::Point(v[2], v[3]), CV_RGB(0,255,0));
+	}
+
+	// Draw corner points
+	cv::circle(dst, corners[0], 3, CV_RGB(255,0,0), 2);
+	cv::circle(dst, corners[1], 3, CV_RGB(0,255,0), 2);
+	cv::circle(dst, corners[2], 3, CV_RGB(0,0,255), 2);
+	cv::circle(dst, corners[3], 3, CV_RGB(255,255,255), 2);
+
+	// Draw mass center
+	cv::circle(dst, center, 3, CV_RGB(255,255,0), 2);
+
+	cv::Mat quad = cv::Mat::zeros(300, 220, CV_8UC3);
+
+	std::vector<cv::Point2f> quad_pts;
+	quad_pts.push_back(cv::Point2f(0, 0));
+	quad_pts.push_back(cv::Point2f(quad.cols, 0));
+	quad_pts.push_back(cv::Point2f(quad.cols, quad.rows));
+	quad_pts.push_back(cv::Point2f(0, quad.rows));
+
+	cv::Mat transmtx = cv::getPerspectiveTransform(corners, quad_pts);
+	cv::warpPerspective(src, quad, transmtx, quad.size());
+
+	cv::imshow("image", dst);
+	cv::imshow("quadrilateral", quad);
+	cv::waitKey();
+	return 0;
+}
+