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what is your OpenCV version? i tested with OpenCV 3.4 and setting IMWRITE_PNG_BILEVEL to 1 seems working

test code:

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.MatOfInt;
import org.opencv.imgcodecs.Imgcodecs;
public class test
{
   public static void main( String[] args )
   {
      System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
      Mat img = new Mat(1000, 1000, CvType.CV_8UC1);
      Core.randu(img, 0, 2);
      MatOfInt parameters = new MatOfInt(
                Imgcodecs.IMWRITE_PNG_BILEVEL, 1
        );
      Imgcodecs.imwrite("c:/test/test.png", img, parameters);
   }
}

result image is 126.283 bayt