Detect license plate

edit

ok i am working on how to detect the plate on different image sizes so i have read from this link that there is technique as follow link

    1.Rectangle check   
     Checking that the candidate regions for plate had rectangle shape by compare white pixels count of these regions to their areas with ±5% tolerance  
 If count of white pixels = ±5% area of these region   
This region may be a plate 
  Else This region not a plate
     2. Plate dimension check 
 The Egyptian plate had a fixed dimension with height equal to 17 cm and width equal to 32 cm, so the ratio between heights to width approximately 1:2.   After rectangle check, the dimension check applied of the succeed regions of rectangle shapes, 
 If 1.5 < width/height of the succeed region <2.5    
            This region may be a plate   
              Else This region not a plate

so after findcontours such if conditions should be applies and here is my code

Mat hierarchy = new Mat();
        Imgproc.findContours(image_threshold.clone(), contours, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_NONE);

//        Rect rectCrop = new Rect();
        Mat m = new Mat();
        for (MatOfPoint contour : contours) {

            Rect rec = Imgproc.boundingRect(contour);

            if (hierarchy.size().height > 0 && hierarchy.size().width > 0) {
                for (int i = 0; i < contours.size(); i++) {

                    if (verifysize(rec)) {
                        System.out.println("first test");
                        Core.extractChannel(contour, m, 0);
                        int n = Core.countNonZero(m);
                        float area = (float) (rec.size().height * (float) rec.size().width); 
                        int minarea = (int) area - (int) (area / 100 * 6);
                        int maxarea = (int) area + (int) (area / 100 * 6);
                        if (minarea < n || n < maxarea) {
                            System.err.println("second test");
//                            Imgproc.drawContours(image, contours, i, new Scalar(0, 0, 255), -1, 8, hierarchy, 0, new Point());
                            Imgproc.rectangle(image, rec.tl(), rec.br(), new Scalar(0, 0, 255), 3);
//                        rectCrop = new Rect(rec.x, rec.y, rec.width, rec.height);
                        }
                    }
                }

            }
            Imgcodecs.imwrite("/home/tomna/NetBeansProjects/MainClass/src/mainclass/121.jpg", image);
        }

public static boolean verifysize(Rect re) {

    float ratio = (float) re.size().width / (float) re.size().height;
    if (1.5 > ratio || ratio > 2.5) {
        return false;
    } else {
        return true;
    }

}