Java OpenCV haarcascade_frontalface_default.xml

Question

import com.googlecode.javacv.cpp.opencv_core.IplImage;
import static com.googlecode.javacv.cpp.opencv_core.*;
import static com.googlecode.javacv.cpp.opencv_highgui.*;
import static com.googlecode.javacv.cpp.opencv_objdetect.*;

public class FaceDetection{

    public static final String XML_FILE = 
            "resources/haarcascade_frontalface_default.xml";

    public static void main(String[] args){

        IplImage img = cvLoadImage("resources/lena.jpg");       
        detect(img);        
    }   

    public static void detect(IplImage src){

        CvHaarClassifierCascade cascade = new 
                CvHaarClassifierCascade(cvLoad(XML_FILE));
        CvMemStorage storage = CvMemStorage.create();
        CvSeq sign = cvHaarDetectObjects(
                src,
                cascade,
                storage,
                1.5,
                3,
                CV_HAAR_DO_CANNY_PRUNING);

        cvClearMemStorage(storage);

        int total_Faces = sign.total();     

        for(int i = 0; i < total_Faces; i++){
            CvRect r = new CvRect(cvGetSeqElem(sign, i));
            cvRectangle (
                    src,
                    cvPoint(r.x(), r.y()),
                    cvPoint(r.width() + r.x(), r.height() + r.y()),
                    CvScalar.RED,
                    2,
                    CV_AA,
                    0);

        }

        cvShowImage("Result", src);
        cvWaitKey(0);

    }           

Exception

OpenCV Error: Unspecified error (The node does not represent a user
object (unknown type?)) in cvRead, file src\persistence.cpp, line 4976
Exception in thread "main" java.lang.RuntimeException:
src\persistence.cpp:4976: error: (-2) The node does not represent a
user object (unknown type?) in function cvRead

Anyone know how to fix this?

Answer 1

As far as I understood, you are trying to pass OpenCV haarcascades XML resource file into cvLoad function, which is not designed to work with Java resource files, since it is a C++ function, which has no idea about this notion.

I had the same problem and the only workaround I found was copying this xml file from Java resource into temporary directory, feed it to cvLoad function and then delete it. It worked. And moreover there is a special OpenCV function for it, which does exactly all that.

I used an example from https://github.com/bytedeco/javacv/blob/master/samples/FaceApplet.java

String classiferName = "haarcascade_frontalface_alt.xml";

// copying xml file into temp directory
File classifierFile = Loader.extractResource(classiferName, null, "classifier", ".xml");
if (classifierFile == null || classifierFile.length() <= 0) {
    throw new IOException("Could not extract \"" + classiferName + "\" from Java resources.");
}

// Preload the opencv_objdetect module to work around a known bug.
Loader.load(opencv_objdetect.class);

classifier = new CvHaarClassifierCascade(cvLoad(classifierFile.getAbsolutePath()));

// deleting temp file
classifierFile.delete();
if (classifier.isNull()) {
     throw new IOException("Could not load the classifier file.");
}

Hope it helps!