这个函数作用是从输入的图像中提取检测到的最大矩形区域，但是对矩形的畸变程度鲁棒性还有待改进，
否则矩形区域的提取可能出现问题；
该函数一般可以用于文档扫描等；
图像输入输出示例：
代码部分如下：
头文件：
#include<opencv2/opencv.hpp>
using namespace std;
using namespace cv;
extern Mat extractedRect;
int RectSegmentation(const Mat& imgIn);
int PreOperation(const Mat& imgIn);
int InContours(Mat& imgIn);
int largestSquare(const vector<vector<Point>>& squares, vector<Point>& largest_square);
int rectExtract(vector<Point>& corners);
double getAngle(Point pt0, Point pt1, Point pt2);
源文件
#include"extract_the_biggest_rectangle.h"
Mat tmpImg, tmpImg2;
Mat grayImg;
vector<Point> largest_square;
static vector<vector<Point>> squaresExp, hullsExp;
double pointDist(Point pt1, Point pt2);
Point2f computeCorner(Vec4i line1, Vec4i line2);
void sortCorners(vector<Point>& points);
int RectSegmentation(const Mat& imgIn)
{
resize(imgIn, tmpImg, Size(), 0.25, 0.25, 1);
tmpImg2 = tmpImg.clone();
PreOperation(tmpImg);
InContours(grayImg);
return 0;
}
int PreOperation(const Mat& imgIn)
{
cvtColor(imgIn, grayImg, COLOR_BGR2GRAY);
GaussianBlur(grayImg, grayImg, Size(3, 3), 0, 0, BORDER_DEFAULT);
return 0;
}
int InContours(Mat& imgIn)
{
Mat CannyImg;
int threshLow = 35;
Canny(imgIn, CannyImg, threshLow, 3 * threshLow, 3);
dilate(CannyImg, CannyImg, Mat(), Point(-1, -1), 10, 1, Scalar(1));
erode(CannyImg, CannyImg, Mat(), Point(-1, -1), 10, 1, Scalar(1));
vector<vector<Point>> contoursExp;
vector<Vec4i> hierarchyExp;
findContours(CannyImg, contoursExp, hierarchyExp, RETR_LIST, CHAIN_APPROX_SIMPLE);
Mat contourImg = tmpImg.clone();
int i = 0;
for (; i >= 0; i = hierarchyExp[i][0]) {
drawContours(contourImg, contoursExp, i, Scalar(0, 255, 255), 2, 8, hierarchyExp);
}
vector<Point> hull, approx;
for (size_t i = 0; i < contoursExp.size(); i++)
{
convexHull(contoursExp[i], hull);
approxPolyDP(hull, approx, arcLength(hull, true)*0.02, true);
if (approx.size() == 4 && fabs(contourArea(Mat(approx))) >= 40000 && isContourConvex(Mat(approx)))
{
double maxCosine = 0;
for (int j = 2; j < 5; j++) {
double tmpCosine = fabs(getAngle(approx[j % 4], approx[j - 2], approx[j - 1]));
maxCosine = MAX(tmpCosine, maxCosine);
}
if (maxCosine <= 0.5) {
squaresExp.push_back(approx);
hullsExp.push_back(hull);
}
}
}
int index = largestSquare(squaresExp, largest_square);
if (largest_square.size() == 0 || index == -1) return -1;
hull = hullsExp[index];
approxPolyDP(Mat(hull), approx, 3, true);
vector<Point> newApprox;
double maxDistance = arcLength(Mat(approx), true)*0.02;
for (Point p : approx) {
if (!(
pointDist(p, largest_square[0]) > maxDistance&&
pointDist(p, largest_square[1]) > maxDistance&&
pointDist(p, largest_square[2]) > maxDistance&&
pointDist(p, largest_square[3]) > maxDistance
)) {
newApprox.push_back(p);
}
}
vector<Vec4i> lines;
for (int i = 0; i < newApprox.size(); i++) {
Point p1 = newApprox[i];
Point p2 = newApprox[(i + 1) % newApprox.size()];
if (pointDist(p1, p2) > 2 * maxDistance) {
lines.push_back(Vec4i(p1.x, p1.y, p2.x, p2.y));
line(grayImg, p1, p2, Scalar(255), 2, 8);
}
}
vector<Point> corners1;
for (int i = 0; i < lines.size(); i++) {
Point corner = computeCorner(lines[i], lines[(i + 1) % lines.size()]);
corners1.push_back(corner);
}
for (int i = 0; i < corners1.size(); i++) {
circle(tmpImg2, corners1[i], 5, Scalar(255, 255, 255), -1);
line(tmpImg2, corners1[i], corners1[(i + 1) % corners1.size()], Scalar(255, 0, 0), 1, 8);
}
imshow("outPutImg", tmpImg2);//
sortCorners(corners1);
rectExtract(corners1);
return 0;
}
double getAngle(Point pt0, Point pt1, Point pt2)
{
double dx1 = pt0.x - pt2.x;
double dy1 = pt0.y - pt2.y;
double dx2 = pt1.x - pt2.x;
double dy2 = pt1.y - pt2.y;
double cos1 = (dx1*dx2 + dy1 * dy2) / sqrt((dx1*dx1 + dy1 * dy1)*(dx2*dx2 + dy2 * dy2) + 1e-10);
return cos1;
}
int largestSquare(const vector<vector<Point>>& squares, vector<Point>& largest_square)
{
if (!squares.size()) return -1;
int maxWidth = 0;
int maxHeight = 0;
int maxIndex = 0;
for (int i = 0; i < squares.size(); i++) {
Rect rectangleIn = boundingRect(Mat(squares[i]));
if ((rectangleIn.width >= maxWidth) && (rectangleIn.height >= maxHeight)) {
maxWidth = rectangleIn.width;
maxHeight = rectangleIn.height;
maxIndex = i;
}
}
largest_square = squares[maxIndex];
return maxIndex;
}
double pointDist(Point pt1, Point pt2) {
int a = pt1.x - pt2.x;
int b = pt1.y - pt2.y;
int c = a * a + b * b;
return sqrt(c);
}
Point2f computeCorner(Vec4i line1, Vec4i line2) {
int x1 = line1[0], y1 = line1[1], x2 = line1[2], y2 = line1[3];
int x3 = line2[0], y3 = line2[1], x4 = line2[2], y4 = line2[3];
double d = ((x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4));
if (d) {
Point2f cornerIn;
cornerIn.x = ((x1*y2 - x2 * y1)*(x3 - x4) - (x1 - x2)*(x3*y4 - x4 * y3)) / d;
cornerIn.y = ((x1*y2 - x2 * y1)*(y3 - y4) - (y1 - y2)*(x3*y4 - x4 * y3)) / d;
return cornerIn;
}
else
return Point2f(-1, -1);
}
int rectExtract(vector<Point>& corners)
{
sortCorners(corners);
Point2f p0 = corners[0];
Point2f p1 = corners[1];
Point2f p2 = corners[2];
Point2f p3 = corners[3];
double space0 = pointDist(p0, p1);
double space1 = pointDist(p1, p2);
double space2 = pointDist(p2, p3);
double space3 = pointDist(p3, p0);
double imgWidth = space1 > space3 ? space1 : space3;
double imgHeight = space0 > space2 ? space0 : space2;
//Add the perspective correction
double paraFix1 = (space3 / space1) > 1 ? (space3 / space1) : (space1 / space3);
double paraFix2 = (space2 / space0) > 1 ? (space2 / space0) : (space0 / space2);
if (paraFix1 > paraFix2) imgHeight = imgHeight * paraFix1;
else imgWidth = imgWidth * paraFix2;
if (imgWidth < imgHeight) {
double temp = imgWidth;
imgWidth = imgHeight;
imgHeight = temp;
Point2f tempPoint = p0;
p0 = p1;
p1 = p2;
p2 = p3;
p3 = tempPoint;//rotate the Image
}
vector<Point2f> cornersIn;
cornersIn.push_back(p0);
cornersIn.push_back(p1);
cornersIn.push_back(p2);
cornersIn.push_back(p3);
Mat imgRect(imgHeight * 2, imgWidth * 2, CV_8UC3);
vector<Point2f> rect_pts;
rect_pts.push_back(Point2f(0, imgRect.rows));
rect_pts.push_back(Point2f(0, 0));
rect_pts.push_back(Point2f(imgRect.cols, 0));
rect_pts.push_back(Point2f(imgRect.cols, imgRect.rows));
Mat transmtx;
transmtx = getPerspectiveTransform(cornersIn, rect_pts);
warpPerspective(tmpImg, imgRect, transmtx, imgRect.size());
cout << "size" << (int)(imgRect.rows) << (int)(imgRect.cols) << endl;
imshow("outPutimg", imgRect);
imwrite("outputImg.jpg", imgRect);
return 0;
}
void sortCorners(vector<Point>& points) {
if (points.size() == 0) return;
Point pl = points[0];
int index = 0;
for (int i = 1; i < points.size(); i++)
{
Point point = points[i];
if (pl.x > point.x)
{
pl = point;
index = i;
}
}
points[index] = points[0];
points[0] = pl;
Point lp = points[0];
for (int i = 1; i < points.size(); i++)
{
for (int j = i + 1; j<points.size(); j++)
{
cv::Point point1 = points[i];
cv::Point point2 = points[j];
if ((point1.y - lp.y*1.0) / (point1.x - lp.x)>(point2.y - lp.y*1.0) / (point2.x - lp.x))
{
cv::Point temp = point1;
points[i] = points[j];
points[j] = temp;
}
}
}
}