Javacv Blob detection

Question

I would like to use some blob detection in my application which is written in Java and thus using JavaCV instead of OpenCV. I found many classes like:

SimpleBlobDetector, CvBlobDetector, CvBlob, ... but I can't find any tutorial or demo/example code to use these in Java. Could anyone please tell me how to use these as I can't figure it out and there's no good documentation for them. Thanks!

Answer 1

I am just in this moment working on the same problem and have a first solution. There's a lot of approaches out there but unfortunately most of them are ugly and slow. My main goal to this point was to stay in the JavaCV/OpenCV-World.

These Links pushed me in the right direction:

1. Blob extraction in OpenCV
2. http://voices.yahoo.com/connected-components-using-opencv-5462975.html?cat=15
3. http://opencv.willowgarage.com/documentation/cpp/structural_analysis_and_shape_descriptors.html#cv-findcontours

Here's a complete Demo class that should show you how it's done. Try it with a black background image with simple objects and sharp corners for best results. Make sure to check the second link above to get informed about what's happening in the code.

import static com.googlecode.javacpp.Loader.sizeof;
import static com.googlecode.javacv.cpp.opencv_core.CV_FILLED;
import static com.googlecode.javacv.cpp.opencv_core.CV_RGB;
import static com.googlecode.javacv.cpp.opencv_core.IPL_DEPTH_8U;
import static com.googlecode.javacv.cpp.opencv_core.cvCreateImage;
import static com.googlecode.javacv.cpp.opencv_core.cvCreateMemStorage;
import static com.googlecode.javacv.cpp.opencv_core.cvDrawContours;
import static com.googlecode.javacv.cpp.opencv_core.cvGetSize;
import static com.googlecode.javacv.cpp.opencv_core.cvPoint;
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_BGR2GRAY;
import static com.googlecode.javacv.cpp.opencv_imgproc.CV_CHAIN_APPROX_SIMPLE;
import static com.googlecode.javacv.cpp.opencv_imgproc.CV_RETR_CCOMP;
import static com.googlecode.javacv.cpp.opencv_imgproc.CV_THRESH_BINARY;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvCvtColor;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvFindContours;
import static com.googlecode.javacv.cpp.opencv_imgproc.cvThreshold;

import java.awt.Color;
import java.util.Random;

import com.googlecode.javacv.cpp.opencv_core.CvContour;
import com.googlecode.javacv.cpp.opencv_core.CvMemStorage;
import com.googlecode.javacv.cpp.opencv_core.CvScalar;
import com.googlecode.javacv.cpp.opencv_core.CvSeq;
import com.googlecode.javacv.cpp.opencv_core.IplImage;

/**
 * A demo for blob extraction using only JavaCV / OpenCV
 * @see https://stackoverflow.com/questions/4641817/blob-extraction-in-opencv
 * @see http://voices.yahoo.com/connected-components-using-opencv-5462975.html?cat=15
 * @see http://opencv.willowgarage.com/documentation/cpp/structural_analysis_and_shape_descriptors.html#cv-findcontours
 * @author happyburnout
 */

public class JavaCVBlobDemo {

    static String sourcePath = "c:/test/source.jpg";
    static String targetPath = "c:/test/target.jpg";

    public static void main (String args[]){
        IplImage image = cvLoadImage(sourcePath);
        IplImage grayImage = cvCreateImage(cvGetSize(image), IPL_DEPTH_8U, 1);
        cvCvtColor(image, grayImage, CV_BGR2GRAY);

        CvMemStorage mem;
        CvSeq contours = new CvSeq();
        CvSeq ptr = new CvSeq();
        cvThreshold(grayImage, grayImage, 150, 255, CV_THRESH_BINARY);
        mem = cvCreateMemStorage(0);

        cvFindContours(grayImage, mem, contours, sizeof(CvContour.class) , CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));

        Random rand = new Random();
        for (ptr = contours; ptr != null; ptr = ptr.h_next()) {
            Color randomColor = new Color(rand.nextFloat(), rand.nextFloat(), rand.nextFloat());
            CvScalar color = CV_RGB( randomColor.getRed(), randomColor.getGreen(), randomColor.getBlue());
            cvDrawContours(image, ptr, color, CV_RGB(0,0,0), -1, CV_FILLED, 8, cvPoint(0,0));
        }
        cvSaveImage(targetPath, image);
    }

}

Answer 2

public static IplImage detectObjects(IplImage srcImage){

    IplImage resultImage = cvCloneImage(srcImage);

    CvMemStorage mem = CvMemStorage.create();
    CvSeq contours = new CvSeq();
    CvSeq ptr = new CvSeq();

    cvFindContours(srcImage, mem, contours, Loader.sizeof(CvContour.class) , CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));

    CvRect boundbox;

    for (ptr = contours; ptr != null; ptr = ptr.h_next()) {
        boundbox = cvBoundingRect(ptr, 0);

        cvRectangle( resultImage, cvPoint( boundbox.x(), boundbox.y() ), cvPoint( boundbox.x() + boundbox.width(), boundbox.y() + boundbox.height()),cvScalar( 0, 255, 255, 0 ), 3, 0, 0 ); 
    }

    return resultImage;
}