Object tracking in Java - detect position of colored spot in image

Red spot in image - position to be detected later

Object Tracking plays important role in Image Processing research projects. In this example, I am showing how we can detect the position [(x, y) coordinates ] of a colored spot in given image using JavaCV (Java wrapper for OpenCV ).



Input image :
This image has a red colored spot. And our objective is to track the position coordinate of the spot in image.The example below uses thresholding in HSV space and simple moment calculations given in OpenCV library.





You can use this code to track an object in a video sequence - say live web-cam capture video.

• The code for capturing webcam using JavaCV is here.
• Help on Configuring a JavaCV project in Eclipse+windows is here.

Detecting Position of a spot in Threshold image:

    static Dimension getCoordinates(IplImage thresholdImage) {
        int posX = 0;
        int posY = 0;        CvMoments moments = new CvMoments();
        cvMoments(thresholdImage, moments, 1);
        // cv Spatial moment : Mji=sumx,y(I(x,y)•xj•yi)
        // where I(x,y) is the intensity of the pixel (x, y).
        double momX10 = cvGetSpatialMoment(moments, 1, 0); // (x,y)
        double momY01 = cvGetSpatialMoment(moments, 0, 1);// (x,y)
        double area = cvGetCentralMoment(moments, 0, 0);
        posX = (int) (momX10 / area);
        posY = (int) (momY01 / area);
        return new Dimension(posX, posY);
    }

The complete working source  Code:

//imports
import static com.googlecode.javacv.cpp.opencv_core.cvCreateImage;
import static com.googlecode.javacv.cpp.opencv_core.cvGetSize;
import static com.googlecode.javacv.cpp.opencv_core.cvInRangeS;
import static com.googlecode.javacv.cpp.opencv_core.cvReleaseImage;
import static com.googlecode.javacv.cpp.opencv_core.cvScalar;
import static com.googlecode.javacv.cpp.opencv_highgui.cvLoadImage;
import static com.googlecode.javacv.cpp.opencv_highgui.cvSaveImage;
import static com.googlecode.javacv.cpp.opencv_imgproc.CV_BGR2HSV;
import static com.googlecode.javacv.cpp.opencv_imgproc.CV_MEDIAN;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvCvtColor;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvSmooth;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvGetSpatialMoment;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvGetCentralMoment;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvMoments;
import java.awt.Dimension;

import com.googlecode.javacv.cpp.opencv_core.IplImage;
import com.googlecode.javacv.cpp.opencv_imgproc.CvMoments;

public class ObjectPositionDetect {
    static int hueLowerR = 160;
    static int hueUpperR = 180;

    public static void main(String[] args) {
        IplImage orgImg = cvLoadImage("finding-red-color-spot.JPG");
        IplImage thresholdImage = hsvThreshold(orgImg);
        cvSaveImage("hsvthreshold.jpg", thresholdImage);
        Dimension position = getCoordinates(thresholdImage);
        System.out.println("Dimension of original Image : " + thresholdImage.width() + " , " + thresholdImage.height());
        System.out.println("Position of red spot    : x : " + position.width + " , y : " + position.height);
    }

    static Dimension getCoordinates(IplImage thresholdImage) {
        int posX = 0;
        int posY = 0;
        CvMoments moments = new CvMoments();
        cvMoments(thresholdImage, moments, 1);
        // cv Spatial moment : Mji=sumx,y(I(x,y)•xj•yi)
        // where I(x,y) is the intensity of the pixel (x, y).
        double momX10 = cvGetSpatialMoment(moments, 1, 0); // (x,y)
        double momY01 = cvGetSpatialMoment(moments, 0, 1);// (x,y)
        double area = cvGetCentralMoment(moments, 0, 0);
        posX = (int) (momX10 / area);
        posY = (int) (momY01 / area);
        return new Dimension(posX, posY);
    }

    static IplImage hsvThreshold(IplImage orgImg) {
        // 8-bit, 3- color =(RGB)
        IplImage imgHSV = cvCreateImage(cvGetSize(orgImg), 8, 3);
        System.out.println(cvGetSize(orgImg));
        cvCvtColor(orgImg, imgHSV, CV_BGR2HSV);
        // 8-bit 1- color = monochrome
        IplImage imgThreshold = cvCreateImage(cvGetSize(orgImg), 8, 1);
        // cvScalar : ( H , S , V, A)
        cvInRangeS(imgHSV, cvScalar(hueLowerR, 100, 100, 0), cvScalar(hueUpperR, 255, 255, 0), imgThreshold);
        cvReleaseImage(imgHSV);
        cvSmooth(imgThreshold, imgThreshold, CV_MEDIAN, 13);
        // save
        return imgThreshold;
    }
}

Outputs :
Thresolding in HSV space : also given in my earlier post

Output of image thresholding in hsv - of image above

Detected Position :

Dimension of original Image : 800 , 600
Position of red spot : x : 84 , y : 320
Demo Video: Drawing by tracking the position of red object