Android: GridView make one image of a different size

I'm trying to get my application to look like this:

However, I'm not able to get the first image to be of a large size. Here is my code for the Adapter:

public class ImageAdapter extends BaseAdapter {
    private Context mContext;

    // create a new ImageView for each item referenced by the Adapter
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;

        int imgSize = 0;

        if (convertView == null) {

            //Size of the screen
            WindowManager wm = (WindowManager) mContext
                    .getSystemService(Context.WINDOW_SERVICE);
            Display display = wm.getDefaultDisplay();
            Point size = new Point();
            display.getSize(size);
            imgSize = size.x / 4;

            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(imgSize,
                    imgSize));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);

        } else {
            imageView = (ImageView) convertView;
        }

        imageView.setImageResource(mThumbIds[position]);

       //Trying to set image of the first column to be two times bigger than small images
        imageView.setLayoutParams(new GridView.LayoutParams(imgSize * 2,
                imgSize * 2));
        imageView.setImageResource(mThumbIds2[0]);

        return imageView;
    }

    public Integer[] mThumbIds = { R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic, R.drawable.mysmallpic,
            R.drawable.mysmallpic, R.drawable.mysmallpic };

    public Integer[] mThumbIds2 = { R.drawable.mybigpic };
}

How would I be able to make my first image bigger that the rest?

Thanks!