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Hello all, I am new to openCV and trying to learn how to write an image recognition application in java. Samples have been tough to find but I am scouring the web. I found an example to train images and create a data file. But even though it compiles it fails on one particular line. Here is the whole source code:

        import java.io.File;

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Size;
import org.opencv.highgui.Highgui;
import org.opencv.ml.CvSVM;
import org.opencv.ml.CvSVMParams;

public class TrainOpenCV {

        protected static final String PATH_POSITIVE = "data/positive/";
        protected static final String PATH_NEGATIVE = "data/negative/";
        protected static final String XML = "data/test.xml";
        protected static final String FILE_TEST = "data/negative/1.jpg";

        private static Mat trainingImages;
        private static Mat trainingLabels;
        private static Mat trainingData;
        private static Mat classes;
        private static CvSVM clasificador;

        static {
            System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
            trainingImages = new Mat();
            trainingLabels = new Mat();
            trainingData = new Mat();
            classes = new Mat();
        }

        public static void main( String[ ] args ) {
            trainPositive();
            trainNegative();
            train();
            test();
        }

        protected static void test() {
            Mat in = Highgui.imread( new File( FILE_TEST ).getAbsolutePath(), Highgui.CV_LOAD_IMAGE_GRAYSCALE );
            clasificador.load( new File( XML ).getAbsolutePath() );
            System.out.println( clasificador );
            Mat out = new Mat();
            in.convertTo( out, CvType.CV_32FC1 );
            out = out.reshape( 1, 1 );
            System.out.println( out );
            System.out.println( clasificador.predict( out ) );
        }

        protected static void train() {
            trainingImages.copyTo( trainingData );
            trainingData.convertTo( trainingData, CvType.CV_32FC1 );
            trainingLabels.copyTo( classes );
            CvSVMParams params = new CvSVMParams();
            params.set_kernel_type( CvSVM.LINEAR );
            System.out.println("c");
               // **** The line below is where it breaks ****
            clasificador = new CvSVM(trainingData, classes, new Mat(), new Mat(), params );
            System.out.println("d");
            clasificador.save( XML );

            }

        protected static void trainPositive() {
            for ( File file : new File( PATH_POSITIVE ).listFiles() ) {
                Mat img = getMat( file.getAbsolutePath() );
                System.out.println("img = "+ img.empty() + img.height());
                trainingImages.push_back( img.reshape( 1, 1 ) );
                trainingLabels.push_back( Mat.ones( new Size( 1, 1 ), CvType.CV_32FC1 ) );
            }
        }

        protected static void trainNegative() {
            for ( File file : new File( PATH_NEGATIVE ).listFiles() ) {
                Mat img = getMat( file.getAbsolutePath() );
                trainingImages.push_back( img.reshape( 1, 1 ) );
                trainingLabels.push_back( Mat.zeros( new Size( 1, 1 ), CvType.CV_32FC1 ) );
            }
        }

        protected static Mat getMat( String path ) {
            Mat img = new Mat();
            Mat con = Highgui.imread( path, Highgui.CV_LOAD_IMAGE_GRAYSCALE );
            con.convertTo( img, CvType.CV_32FC1, 1.0 / 255.0 );
            return img;
        }

}

When it hits the line "clasificador = new CvSVM(trainingData, classes, new Mat(), new Mat(), params );" I get the following error:

"OpenCV Error: Bad argument (There is only a single class) in cvPreprocessCategoricalResponses, file ........\opencv\modules\ml\src\inner_functions.cpp, line 729 Exception in thread "main" CvException [org.opencv.core.CvException: cv::Exception: ........\opencv\modules\ml\src\inner_functions.cpp:729: error: (-5) There is only a single class in function cvPreprocessCategoricalResponses ] at org.opencv.ml.CvSVM.CvSVM_1(Native Method) at org.opencv.ml.CvSVM.<init>(CvSVM.java:90) at TrainOpenCV.train(TrainOpenCV.java:71) at TrainOpenCV.main(TrainOpenCV.java:35)"

I appreciate any help!