Number plate localization in bulk of images - c++

Question

I have got bulk of car images and want to perform automatic number plate recognition but i am stuck at localization phase .I want to get license plate individually as output on which i can perform recognition.Here is my code for localization:
int main(int args,char* argv)
{
//String filename;
//filename="";
cv::Mat image=cv::imread("C:\\Users\\Sarora\\Downloads\\Images\\frame_1375.jpg",CV_LOAD_IMAGE_COLOR);
cv::Mat img;
cv::Mat img_sobel;
cv::Mat grad_x, grad_y;
cv::Mat abs_grad_x, abs_grad_y;
cv::Mat imgContours;
//vector <Plate>result;
cv::cvtColor(image, img, CV_BGR2GRAY);
blur(img, img, cv::Size(5,5));
//cv::namedWindow("Img1.jpg", CV_WINDOW_AUTOSIZE );
//sobel filter applied on image..............................................................................................
cv::Sobel(img, grad_x, CV_16S, 1, 0,3,1,0, cv::BORDER_DEFAULT);
convertScaleAbs( grad_x, abs_grad_x );
cv::Sobel(img, grad_y, CV_16S, 0, 1,3,1,0, cv::BORDER_DEFAULT);
convertScaleAbs( grad_y, abs_grad_y );
addWeighted( abs_grad_x, 0.5, abs_grad_y, 0.5, 0, img_sobel );
cv::imwrite("Img2.jpg",img_sobel);
//Threshold the image...................................................................................................................
cv::Mat Thresh_img;
threshold(img_sobel, Thresh_img, 0, 255, CV_THRESH_OTSU+CV_THRESH_BINARY);
//imshow("Threshold", Thresh_img);
//Morphological close operation applied................................................................................................
cv::Mat element1=cv::getStructuringElement(cv::MORPH_RECT, cv::Size(3, 3));
cv::morphologyEx(Thresh_img,Thresh_img,CV_MOP_CLOSE,element1);
cv::imwrite("Close1.jpg",Thresh_img);
//cv::waitKey(5000);
//find Contours of whole image......................................................................................................
std::vector <std::vector<cv::Point>> contours;
cv::findContours(Thresh_img, contours,CV_RETR_LIST,CV_CHAIN_APPROX_NONE);
//cv::drawContours(image,contours,-1,cv::Scalar(0,0,255),3);
cv::imwrite("Contours1.jpg",image);
std::vector <std::vector<cv::Point>>::iterator itc= contours.begin();
std::vector <cv::RotatedRect> rects;
//vector<vector<Point> > contours_poly(rects.size());
//vector<Rect> boundRect(rects.size());
//Remove patch not inside the limits of aspect ratio and area..................................................................................
while (itc!=contours.end()) {
cv::RotatedRect mr= cv::minAreaRect(cv::Mat(*itc));
if( !verifySizes(mr))
{ itc= contours.erase(itc);
}else {
++itc;
rects.push_back(mr);
}
}
cv::Mat drawing;
vector<vector<cv::Point> > contours_poly(rects.size());
vector<cv::Rect> boundRect(rects.size());
//Draw contours
cv::Mat output;
image.copyTo(output);
for(int i=0;i<rects.size();i++)
{
approxPolyDP(cv::Mat(contours[i]), contours_poly[i], 10, true);
boundRect[i] = cv::boundingRect(cv::Mat(contours_poly[i]));
}
//cv::imwrite("Contours.jpg", output);
for (int i = 0; i < rects.size(); i++)
{
drawContours(output, contours_poly, i, CV_RGB(255, 255, 255), 1, 8, vector<cv::Vec4i>(), 0, cv::Point());
//rectangle(output, boundRect[i].tl(), boundRect[i].br(), CV_RGB(0, 255, 0), 3, 8, 0);
}
cv::imwrite("drawing1.jpg",output);
}
bool verifySizes(cv::RotatedRect mr){
float error=0.4;
//Set a min and max area. All other patches are discarded
int min= 5; // minimum area
int max=1000; // maximum area
//Get only patches that match
float rmin= 1;
float rmax= 10;
int area= mr.size.height * mr.size.width;
float r= (float)mr.size.width / (float)mr.size.height;
if(r<1)
r= (float)mr.size.height / (float)mr.size.width;
if(( area < min || area > max ) || ( r < rmin || r > rmax )){
return false;
}else{
return true;
}
}
I have performed sobel filter,Threshold(OTSU+binary),Morphological operation CLOSE,findContours(),removal of one not inside limits of area and aspect ratio and approxPolyDP on the imageThis is my input image
This is approxPolyDP image
Problem is output image is not forming rectangles around License plate.Can anyone tell what is wrong in the code and also how can i proceed further to automatically find license plates in bulk of images?I am confused.
Thank you