def calculate_xy_coords(image_size, screen_size):
    """Calculates x and y coordinates used to display image centered on screen.
    Args:
        image_size as tuple (int width in pixels, int height in pixels).
        screen_size as tuple (int width in pixels, int height in pixels).
    Returns:
        tuple (int x coordinate, int y coordinate).
    """
    image_width, image_height = image_size
    screen_width, screen_height = screen_size
    x = (screen_width - image_width) / 2
    y = (screen_height - image_height) / 2
    return (x, y)