How to find and draw contour around license plate in java?

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Java

OpenCV

I try to detect the license plate from image.

My steps:

1/ Filter noise (Smooth Gaussian)

2/Convert to gray Image

3/ThresholdBinary

4/Dilation and Erosion

5/ Cany filter and findCOntours

But I have a problem with find and draw contours around the license. I am binner in java.Please help me. Thanks very much.

Here is my code:

public class ex1 {
public static void main(String[] args) {
    //read image
    IplImage orgImg = cvLoadImage("F:\\bs9.jpg");
    //smooth Gaussian
    cvSmooth(orgImg,orgImg,CV_GAUSSIAN,7);
    // gray image
    IplImage grayImg = cvCreateImage(cvGetSize(orgImg),orgImg.depth(),1);
    cvCvtColor(orgImg,grayImg,CV_BGR2GRAY);
    //Threshold binary
    cvThreshold(grayImg,grayImg,230,255,CV_THRESH_BINARY_INV);      


    //dalition - erosion

    cvErode(grayImg,grayImg,null,3);
    cvDilate(grayImg,grayImg,null,2);

    // canny filter
    IplImage egde = cvCreateImage(cvSize(grayImg.width(),grayImg.height()),IPL_DEPTH_8U,1);
    cvCanny(grayImg,egde,140,240,7);
    // show image
    cvShowImage("org",orgImg);
    cvShowImage("binary",grayImg);
    cvShowImage("edge",egde);
    //save image
    cvWaitKey();