如何关闭图片末尾附近的对象边缘（打开cv）

Question

我正在编写一个代码来检测图片中框的边缘，但附在图片边缘的框有缺少的行。

如上所述，第一个方块只有2条线出现。 我正在使用open cv C ++ 这是我的代码

cv::Mat src;
cv::Mat gray;
cv::Mat dst;
std::vector<std::vector<cv::Point> > contours;
std::vector<std::vector<cv::Point> > contours2;
std::vector<cv::Point> approx;
Mat img = imread("shapes-noisy.jpg", CV_LOAD_IMAGE_COLOR);
Mat _color = img.clone();
threshold(img, img, 250, 255, 0);
src = img;
cv::cvtColor(src, gray, CV_BGR2GRAY);
Mat img6, img7, img8, img9, img10;
cv::threshold(gray, img6, 250, 255.0, THRESH_BINARY);
Mat element = getStructuringElement( MORPH_RECT,Size(3, 3 ), Point( 1, 1 ) );
dilate( img6, img6, element);
Laplacian(img6, img7, CV_16S, 3, 1, 0, BORDER_DEFAULT);
convertScaleAbs(img7, img8);
vector<Vec4i> hierarchy;
RNG rng(0);
Scalar value;
cv::findContours(img8.clone(), contours, hierarchy,CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
Mat drawing,drawing2;
medianBlur(img8, drawing, 3);
threshold(drawing, drawing, 255, 0, 1);
threshold(drawing, drawing2, 255, 0, 1);
cv::findContours(img8.clone(), contours2, hierarchy,CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
for( int i = 0; i< contours.size(); i++ )
 {
       cv::approxPolyDP(cv::Mat(contours[i]), approx, 10, true);
       if(approx.size() > 3){
       Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
       drawContours( drawing2, contours2, i, color, 2, 8, hierarchy, 0, Point(0,0) );
       }
}

imshow("approx", drawing2);