我在研究膨胀效应，我引用了下面的链接：https://math.stackexchange.com/questions/266250/explanation-of-this-image-warping-bulge-filter-algorithm 示例图像都是nxn类型，如果图像是mxn怎么办。我试图编写代码，但它总是抛出异常：行超出界限。我的代码如下：

public static Picture positionalTransform(Picture picture) {
        int w = picture.width();
        int h = picture.height();

        double X = 0;
        double Y = 0;

        Picture newPic = new Picture(w,h);

        for(int x=0; x<w; x++){
            for(int y=0; y<h; y++){
                X = x - x/2;
                Y = y - y/2;
                double r = Math.hypot(X, Y);
                double angle = Math.atan2(X, Y);
                double rn = Math.pow(r, 2.5)/0.5;

                X = (int) (rn * Math.sin(angle) + x/2);
                Y = (int) (rn * Math.cos(angle) + y/2);

                newPic.setColor((int)X, (int)Y, picture.getColor(x, y));                                    
            }
        }      
        picture = newPic;
        return picture;
    }