private Picture edgeDetector(
                      Picture picture,int threshold){
    for(int row = 0;row < butterflyHeight - 1;row++){
      for(int col = 0;col < butterflyWidth - 1;col++){
        pix1 = picture.getPixel(col,row);
        displayPixel = display.getPixel(col,row);

        //First process two adjacent pixels on the
        // same row.
        pix2 = picture.getPixel(col + 1,row);

        //Get and save the color distance between the
        // two pixels.
        distance = pix1.colorDistance(pix2.getColor());

        //Compare the color distance to the threshold
        // and set the color of the pixel in the
        // display picture accordingly.
        if(distance > threshold){
          displayPixel.setColor(Color.RED);
        }else{
          displayPixel.setColor(Color.WHITE);
        }//end else