public static Picture randomPicture(int W, int H) {
        Picture p = new Picture(W, H);
        for (int i = 0; i < W; i++)
            for (int j = 0; j < H; j++) {
                int r = StdRandom.uniform(255);
                int g = StdRandom.uniform(255);
                int b = StdRandom.uniform(255);
                Color c = new Color(r, g, b);
                p.set (i, j, c);
            }
        return p;
    }