图像的透视变换（opencv2实现）

#include <opencv2/imgproc/imgproc.hpp>

#include <opencv2/highgui/highgui.hpp>

#include <iostream>

#include <cv.h>

using namespace std;

using namespace cv;

Point2f center(0,0);

Point2f computeIntersect(Vec4i a, 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)))
//若d=0，则直线AB与CD平行或重合

{

Point2f pt;

pt.x = ((x1 * y2 - y1 * x2) * (x3 - x4) - (x1 - x2) * (x3 * y4 - y3 * x4)) / d; //求两条直线的交点x坐标

pt.y = ((x1 * y2 - y1 * x2) * (y3 - y4) - (y1 - y2) * (x3 * y4 - y3 * x4)) / d; //求两条直线的交点x坐标

return pt;

}

else

return Point2f(-1, -1);

}

void sortCorners(std::vector<Point2f>& corners,Point2f center)

{

vector<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]);

}

corners.clear();

if (top.size() == 2 && bot.size() == 2){

Point2f tl = top[0].x > top[1].x ? top[1] : top[0];

Point2f tr = top[0].x > top[1].x ? top[0] : top[1];

Point2f bl = bot[0].x > bot[1].x ? bot[1] : bot[0];

Point2f br = bot[0].x > bot[1].x ? bot[0] : bot[1];

corners.push_back(tl);

corners.push_back(tr);

corners.push_back(br);

corners.push_back(bl);

}

}

int main()

{

Mat srcImage = imread("E:\\图片\\image.jpg");//原图

if (srcImage.empty())

return -1;

Mat grayImage; //灰度图

cvtColor(srcImage, grayImage, CV_BGR2GRAY); //转化为灰度图

blur(grayImage, grayImage, Size(3, 3)); //滤波

Canny(grayImage, grayImage, 100, 100, 3);

vector<Vec4i> lines; //直线输出向量

HoughLinesP(grayImage, lines, 1, CV_PI/180, 70, 30, 10); //霍夫直线检测

// 延伸直线

for (int i = 0; i < lines.size(); i++)

{

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] = srcImage.cols;

lines[i][3] = ((float)v[1] - v[3]) / (v[0] - v[2]) * (srcImage.cols - v[2]) + v[3];

}

vector<Point2f> corners;

for (int i = 0; i < lines.size(); i++)

{

for (int j = i+1; j < lines.size(); j++)

{

Point2f pt = computeIntersect(lines[i], lines[j]);//调用自定义函数求相交直线的交点

if (pt.x >= 0 && pt.y >= 0)

corners.push_back(pt);

}

}

vector<Point2f> approx;

approxPolyDP(Mat(corners), approx, arcLength(Mat(corners), true) * 0.02, true);
//approxPolyDP //arcLength计算轮廓周长或曲线长度

if (approx.size() != 4)

{

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); //调用自定义函数

if (corners.size() == 0){

cout << "The corners were not sorted correctly!" << std::endl;

return -1;

}

Mat dst = srcImage.clone();

// Draw lines

for (int i = 0; i < lines.size(); i++)

{

Vec4i v = lines[i];

line(dst, Point(v[0], v[1]), Point(v[2], v[3]), CV_RGB(0,255,0));

}

// Draw corner points

circle(dst, corners[0], 3, CV_RGB(255,0,0), 2);

circle(dst, corners[1], 3, CV_RGB(0,255,0), 2);

circle(dst, corners[2], 3, CV_RGB(0,0,255), 2);

circle(dst, corners[3], 3, CV_RGB(255,255,255), 2);

// Draw mass center

circle(dst, center, 3, CV_RGB(255,255,0), 2);

Mat quad = Mat::zeros(300, 220, CV_8UC3);

vector<Point2f> quad_pts;

quad_pts.push_back(Point2f(0, 0));

quad_pts.push_back(Point2f(quad.cols, 0));

quad_pts.push_back(Point2f(quad.cols, quad.rows));

quad_pts.push_back(Point2f(0, quad.rows));

Mat transmtx = getPerspectiveTransform(corners, quad_pts);
//getPerspectiveTransform由四对点计算透射变换

warpPerspective(srcImage, quad, transmtx, quad.size());
//warpPerspective对图像进行透视变换

imshow("image", dst);

imshow("quadrilateral", quad);

waitKey();

return 0;

}