[置顶] 自动透视校正为四边形对象

参考opencv开源上的，跑通了  注释了一下，以便后续学习

 

 

#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];

	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 (unsigned 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();
	//注意以下存放顺序是顺时针，当时这里出错了，如果想任意顺序下文开辟的四边形矩阵注意对应
	corners.push_back(tl);
	corners.push_back(tr);
	corners.push_back(br);
	corners.push_back(bl);

}

算法流程：先彩色转灰度，然后模糊求canny边缘，再用hough检测直线，求出四线交点，利用opencv自带的求透视矩阵的函数求出透视矩阵，然后利用透视矩阵转换源图像所需的四边形，效果图后续见图片：

int main()
{
	cv::Mat src = cv::imread("C:/Users/Public/Pictures/Sample Pictures/perspective-quadrilateral-src-img.jpg");
	if (src.empty())
	{
		return -1;
	}

	cv::Mat bw;
	cv::cvtColor(src,bw,CV_BGR2GRAY);

	imshow("gray_src",bw);
	cv::blur(bw,bw,cv::Size(3,3));

	imshow("blur",bw);
	cv::Canny(bw,bw,100,100,3);

	imshow("cannyblur",bw);
	std::vector<cv::Vec4i> lines;
	cv::HoughLinesP(bw,lines,1,CV_PI/180,70,30,10);
	//1像素分辨能力  1度的角度分辨能力		>70可以检测成连线		30是最小线长
	//在直线L上的点（且点与点之间距离小于maxLineGap=10的）连成线段，然后这些点全部删除，并且记录该线段的参数，就是起始点和终止点



	//needed for visualization only//这里是将检测的线调整到延长至全屏，即射线的效果，其实可以不必这么做
	for (unsigned 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;//线的交点存储
	for (unsigned int i = 0;i<lines.size();i++)
	{
		for (unsigned 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（四边形）!"<<std::endl;
		return -1;
	}

	//get mass center
	for (unsigned 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 (unsigned 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));	//目标版块画绿线 
	}

	//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);//设定校正过的图片从320*240变为300*220

	//corners of the destination image
	std::vector<cv::Point2f> quad_pts;
	quad_pts.push_back(cv::Point2f(0,0));
	quad_pts.push_back(cv::Point2f(quad.cols,0));//(220,0)
	quad_pts.push_back(cv::Point2f(quad.cols,quad.rows));//(220,300)
	quad_pts.push_back(cv::Point2f(0,quad.rows));

	// Get transformation matrix
	cv::Mat transmtx = cv::getPerspectiveTransform(corners,quad_pts);	//求源坐标系（已畸变的）与目标坐标系的转换矩阵

	// Apply perspective transformation透视转换
	cv::warpPerspective(src,quad,transmtx,quad.size());
	cv::imshow("src",src);
	cv::imshow("image",dst);
	cv::imshow("quadrilateral",quad);

	cv::waitKey();
	return 0;
}

参考网址http://opencv-code.com/tutorials/automatic-perspective-correction-for-quadrilateral-objects/