function averageColor(image img, int start_x, int start_y, int width, int height) {
    int r, g, b;
    for (int x = start_x; x < start_x + width; ++x) {
        for (int y = start_y; y < start_y + height; ++y) {
            r, g, b += img.at(x, y);
        }
    }
    int num_tiles = width * height;
    r, g, b = (x / num_tiles for x in r, g, b)
    return pixel(r, g, b);
}
function shrink(image largeImage, int x_tiles, int y_tiles) {
    int tile_width = int(largeImage.width / x_tiles);
    int tile_height = int(largeImage.height / y_tiles);
    image smallImage(x_tiles, y_tiles);
    for (int x = 0, sx = 0; x < largeImage.size; x += tile_width, ++sx) {
        for (int y = 0, sy = 0; y < largeImage.size; y += tile_height, ++sy) {
            pixel p = averageColor(largeImage, x, y, tile_width, tile_height);
            smallImage.at(sx, sy) = p;
        }
    }
    return smallImage;
}