Calculate white areas pixels in contours using opencv and Javacv

Question

I have develop a program to detect motions using JavaCV. up to now i have completed cvFindContours of the processed image. source code is given below,

public class MotionDetect {

public static void main(String args[]) throws Exception, InterruptedException {

    //FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(new File("D:/pool.avi"));
    OpenCVFrameGrabber grabber = new OpenCVFrameGrabber("D:/2.avi");
    final CanvasFrame canvas = new CanvasFrame("My Image");
    final CanvasFrame canvas2 = new CanvasFrame("ROI");
    canvas.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
    grabber.start();
    IplImage frame = grabber.grab();
    CvSize imgsize = cvGetSize(frame);
    IplImage grayImage = cvCreateImage(imgsize, IPL_DEPTH_8U, 1);
    IplImage ROIFrame = cvCreateImage(cvSize((265 - 72), (214 - 148)), IPL_DEPTH_8U, 1);
    IplImage colorImage;
    IplImage movingAvg = cvCreateImage(imgsize, IPL_DEPTH_32F, 3);
    IplImage difference = null;
    IplImage temp = null;
    IplImage motionHistory = cvCreateImage(imgsize, IPL_DEPTH_8U, 3);


    CvRect bndRect = cvRect(0, 0, 0, 0);
    CvPoint pt1 = new CvPoint(), pt2 = new CvPoint();
    CvFont font = null;

    //Capture the movie frame by frame.
    int prevX = 0;
    int numPeople = 0;
    char[] wow = new char[65];

    int avgX = 0;

    //Indicates whether this is the first time in the loop of frames.
    boolean first = true;

    //Indicates the contour which was closest to the left boundary before the object
    //entered the region between the buildings.
    int closestToLeft = 0;
    //Same as above, but for the right.
    int closestToRight = 320;


    while (true) {
        colorImage = grabber.grab();
        if (colorImage != null) {
            if (first) {
                difference = cvCloneImage(colorImage);
                temp = cvCloneImage(colorImage);
                cvConvertScale(colorImage, movingAvg, 1.0, 0.0);
                first = false;
                //cvShowImage("My Window1", difference);
            } //else, make a running average of the motion.
            else {
                cvRunningAvg(colorImage, movingAvg, 0.020, null);
            }

            //Convert the scale of the moving average.
            cvConvertScale(movingAvg, temp, 1.0, 0.0);

            //Minus the current frame from the moving average.
            cvAbsDiff(colorImage, temp, difference);

            //Convert the image to grayscale.
            cvCvtColor(difference, grayImage, CV_RGB2GRAY);
            //canvas.showImage(grayImage);
            //Convert the image to black and white.
            cvThreshold(grayImage, grayImage, 70, 255, CV_THRESH_BINARY);

            //Dilate and erode to get people blobs
            cvDilate(grayImage, grayImage, null, 18);
            cvErode(grayImage, grayImage, null, 10);
            canvas.showImage(grayImage);


            ROIFrame = cvCloneImage(grayImage);
            cvSetImageROI(ROIFrame, cvRect(72, 148, (265 - 72), (214 - 148)));
            //cvOr(outFrame, tempFrame, outFrame);
            cvShowImage("ROI Frame", ROIFrame);



            cvRectangle(colorImage, /* the dest image */
                    cvPoint(72, 148), /* top left point */
                    cvPoint(265, 214), /* bottom right point */
                    cvScalar(255, 0, 0, 0), /* the color; blue */
                    1, 8, 0);

            CvMemStorage storage = cvCreateMemStorage(0);
            CvSeq contour = new CvSeq(null);
            cvFindContours(grayImage, storage, contour, Loader.sizeof(CvContour.class),  CV_RETR_CCOMP,  CV_CHAIN_APPROX_SIMPLE);

        }




            //Show the frame.
            cvShowImage("My Window", colorImage);

            //Wait for the user to see it.
            cvWaitKey(10);

        }

        //If this is the first time, initialize the images.

        //Thread.sleep(50);
    }

   }
}

In this code ROIFrame, i need to calculate white contours area or pixel numbers??.. is there any way that i can proceed with

cyberdecker · Answer 1 · 2012-11-13T15:50:12.317

2

Use the function cvContourArea() Documentation here.

In your code, after your cvFindContours, do a loop with all of your contours like as:

CvSeq* curr_contour = contour;

while (curr_contour != NULL) {
   area = fabs(cvContourArea(curr_contour,CV_WHOLE_SEQ, 0));
   current_contour = current_contour->h_next;
}

Don't forget to store the area somewhere.

edited Nov 13 '12 at 15:50

answered Nov 13 '12 at 15:45

cyberdecker

574
12
24

really appreciate your answer. what if i want to calculate the white pixel how im going to do that – thusi Nov 13 '12 at 16:21
But you binarize the image before finding the contours, right? Everything will be black or white after the thresholding, so the cvContourArea will calculate the area for each contour (that include the white pixels). – cyberdecker Nov 14 '12 at 11:16
thanks got it. i managed to do it with cvContourArea.. thanks again – thusi Nov 14 '12 at 14:05

Calculate white areas pixels in contours using opencv and Javacv

1 Answers1