CovarianceReducer.java

package org.hipi.tools.covar;

import org.hipi.opencv.OpenCVMatWritable;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Reducer;
import org.bytedeco.javacpp.opencv_core;
import org.bytedeco.javacpp.opencv_core.Mat;
import org.bytedeco.javacpp.opencv_core.Scalar;

import java.io.IOException;

public class CovarianceReducer extends
    Reducer<IntWritable, OpenCVMatWritable, NullWritable, OpenCVMatWritable> {

  @Override
  public void reduce(IntWritable key, Iterable<OpenCVMatWritable> values, Context context)
      throws IOException, InterruptedException {
    
    int N = Covariance.patchSize;
    
    Mat cov = new Mat(N * N, N * N, opencv_core.CV_32FC1, new Scalar(0.0));
    
    // Consolidate covariance matrices
    for(OpenCVMatWritable value : values) {
      opencv_core.add(value.getMat(), cov, cov);
    }
      
    context.write(NullWritable.get(), new OpenCVMatWritable(cov));
  }
}