public static void initializeImages() 
    {
        if(images == null) 
        {
            GreenfootImage baseImage = new GreenfootImage("wave.png");
            images = new GreenfootImage[NUMBER_IMAGES];
            int i = 0;
            while (i < NUMBER_IMAGES) 
            {
                int size = (i+1) * ( baseImage.getWidth() / NUMBER_IMAGES );
                images[i] = new GreenfootImage(baseImage);
                images[i].scale(size, size);
                i++;
            }
        }
    }