Question

当我运行这个应该检测图像中的圆圈的程序时，当我调用drawCircles（）

时，我会在最后一个方法中获得数组索引超出范围的异常

findCircle（）读取图像并搜索圆圈，drawCircles（）使用Bresenaham算法绘制它们。

public class Assig1 {

    public static void main(String[] args) {
        try {
            // arg 0 is the input image name
            BufferedImage img = ImageIO.read(new File(args[0]));

            // arg 1 is the min radius
            int minr = Integer.parseInt(args[1]);
            // arg 2 is the max radius
            int maxr = Integer.parseInt(args[2]);

            // if present, arg 3 is the max width we consider
            int w = (args.length>3) ? Integer.parseInt(args[3]) : img.getWidth();
            // if present, arg 4 is the max height we consider
            int h = (args.length>4) ? Integer.parseInt(args[4]) : img.getHeight();

            // you can look at pixel values with this API call:
            int c = img.getRGB(0,0); // get RGB value of pixel at (0,0)

            // you can write out pixels with the setRGB() API.  However,
            // what you get will depend on the colour model, so here
            // we use a Graphics2D object.

            // graphical output
            Graphics2D g2 = img.createGraphics();
            // use red
            g2.setColor(Color.RED);

            // call circle drawing algorithm
           drawCircle(5,5,3,img,g2);


            //-----
            findCircle(minr,img, w, h);

            //----

            // write out the image
            File outputfile = new File("outputimage1.png");
            ImageIO.write(img, "png", outputfile);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // Bresenham's algorithm to draw a circle
    // requires circle center and radius, as well as the
    // image and Graphics2D object with drawing colour already set.
    static void drawCircle(int cx,int cy,int r,BufferedImage img,Graphics2D g) {
        int f = 1-r;
        int ddF_x = 1;
        int ddF_y = -2 * r;
        int x = 0;
        int y = r;

        // draw cardinal points
        g.drawLine(cx,cy+r,cx,cy+r);
        g.drawLine(cx,cy-r,cx,cy-r);
        g.drawLine(cx+r,cy,cx+r,cy);
        g.drawLine(cx-r,cy,cx-r,cy);

        // draw 1/8 of the circle, taking advantage of symmetry
        while(x < y) {
            if(f >= 0) {
                y--;
                ddF_y += 2;
                f += ddF_y;
            }
            x++;
            ddF_x += 2;
            f += ddF_x;

            g.drawLine(cx+x,cy+y,cx+x,cy+y);
            g.drawLine(cx-x,cy+y,cx-x,cy+y);
            g.drawLine(cx+x,cy-y,cx+x,cy-y);
            g.drawLine(cx-x,cy-y,cx-x,cy-y);
            g.drawLine(cx+y,cy+x,cx+y,cy+x);
            g.drawLine(cx-y,cy+x,cx-y,cy+x);
            g.drawLine(cx+y,cy-x,cx+y,cy-x);
            g.drawLine(cx-y,cy-x,cx-y,cy-x);
        }

    }

    static void findCircle(int r,BufferedImage img, int w, int h) {

        //getting all the pixels from an image
        int[][] pixels = new int[w][h];

        for( int i = 0; i < w; i++ ){
             for( int j = 0; j < h; j++ ){
                   pixels[i][j] = img.getRGB( i, j );
             }
        }

         // graphical output
        Graphics2D g2 = img.createGraphics();
        // use red
        g2.setColor(Color.RED);


        for (int i1=0; i1<pixels.length; i1++) {
             for (int j1=0; j1<pixels[i1].length; j1++) {

                 if(pixels[i1][j1] != pixels[i1+r][j1]
                        || pixels[i1][j1] != pixels[i1-r][j1]
                        || pixels[i1][j1] != pixels[i1][j1+r]
                        || pixels[i1][j1] != pixels[i1][j1-r]){
                    drawCircle(i1,j1,r,img,g2);
                }
             }

         }
    }
}

Answer 1

在findCircle方法中，

        if(pixels[i1][j1] != pixels[i1+r][j1]
                || pixels[i1][j1] != pixels[i1-r][j1]
                || pixels[i1][j1] != pixels[i1][j1+r]
                || pixels[i1][j1] != pixels[i1][j1-r]){
            drawCircle(i1,j1,r,img,g2);
        }

如果r不是0，这将导致数组索引超出范围异常，因为您基本上是从第0个索引循环到第n个索引。基本上你在增加或减去r的任何地方。例如，这是导致此错误的语句之一

pixels[i1+r][j1]

数组索引超出范围异常

1 个答案: