ovelayImage JAVA API

    void overlayImage(Mat background,Mat foreground,Mat output,Point location){
        Log.i("call","Calling OVerlay Image");
        background.copyTo(output);
        // start at the row indicated by location, or at row 0 if location.y is negative.
        for(int y = (int) Math.max(location.y , 0); y < background.rows(); ++y){
            int fY = (int) (y - location.y); // because of the translation
            // we are done of we have processed all rows of the foreground image.
            if(fY >= foreground.rows())
                break;
            // start at the column indicated by location,
            // or at column 0 if location.x is negative.
            for(int x = (int) Math.max(location.x, 0); x < background.cols(); ++x){
                int fX = (int) (x - location.x); // because of the translation.
                // we are done with this row if the column is outside of the foreground image.
                if(fX >= foreground.cols()){
                    break;
                }
                //determine the opacity of the foregrond pixel, using its fourth (alpha) channel.
                /// here tried other type of arrays like short , int and float but same problem is there
                double[] opacity = new double[(int) (foreground.total()*foreground.channels())];
                /// Mat type not compatible error over here
                foreground.get(fY , fX, opacity);

                                    ///OR
                //double[] opacity = foreground.get(fY , fX, opacity);
                Log.i("Length", String(opacity.length));

                /// assuming that opacity will be array of 4 values and
                /// opacity[3] will contain alpha channel values
                if ( opacity[3] > 0){
                    double[] foregroundPx = foreground.get(fY, fX);
                    double[] backgroundPx = background.get(fY, fX);
                    double[] finalPixelValue = new double[3] ;
                    finalPixelValue[0] = backgroundPx[0] * ( 1.0 - opacity[3]) + foregroundPx[0] * opacity[3];
                    finalPixelValue[1] = backgroundPx[1] * ( 1.0 - opacity[3]) + foregroundPx[1] * opacity[3];
                    finalPixelValue[2] = backgroundPx[2] * ( 1.0 - opacity[3]) + foregroundPx[2] * opacity[3];
                    output.put(fY, fX,finalPixelValue);
                }
            }
        }
    }