How do I divide a picture into 4 sections and change each section?

In the body of the Picture class create a new public method named "specialEffect" that has return type void and takes no parameters. The method should contain four loops that each iterate over the pixels of an image in such a way that each loop itera开发者_运维知识库tes through 1/4 of the total number of pixels and performs a different effect as follows: The first loop is to apply an effect that removes the both the blue and green component from each pixel leaving the red component unchanged. The next loop continuing from where the last left off is to remove the blue and red component from each pixel leaving the green component unchanged. The next loop continuing from where the last left off it to remove the green and red component from each pixel leaving the blue component unchanged. The final loop continuing from where the last off is to convert each pixel to greyscale.

How would I go about doing that? I only know how to divide it in half and change the top part.. not sure how to go about doing sections.

Thanks!

The code below produces this picture:

private static BufferedImage specialEffect(BufferedImage in) {

    BufferedImage out = new BufferedImage(in.getWidth(), in.getHeight(), 
            BufferedImage.TYPE_INT_ARGB);

    for (int x = 0; x < out.getWidth() / 2; x++) {
        for (int y = 0; y < out.getHeight() / 2; y++) {
            Color c = new Color(in.getRGB(x, y));
            out.setRGB(x, y, new Color(c.getRed(), 0, 0).getRGB());
        }
    }
    for (int x = out.getWidth() / 2; x < out.getWidth(); x++) {
        for (int y = 0; y < out.getHeight() / 2; y++) {
            Color c = new Color(in.getRGB(x, y));
            out.setRGB(x, y, new Color(0, c.getGreen(), 0).getRGB());
        }
    }
    for (int x = 0; x < out.getWidth() / 2; x++) {
        for (int y = out.getHeight() / 2; y < out.getHeight(); y++) {
            Color c = new Color(in.getRGB(x, y));
            out.setRGB(x, y, new Color(0, 0, c.getBlue()).getRGB());
        }
    }
    for (int x = out.getWidth() / 2; x < out.getWidth(); x++) {
        for (int y = out.getHeight() / 2; y < out.getHeight(); y++) {
            Color c = new Color(in.getRGB(x, y));
            int m = Math.max(c.getRed(),Math.max(c.getGreen(),c.getBlue()));
            out.setRGB(x, y, new Color(m, m, m).getRGB());
        }
    }

    return out;
}

public static void main(String[] args) throws IOException {
    JFrame frame = new JFrame("Test");

    frame.add(new JComponent() {

         BufferedImage image = specialEffect(ImageIO.read(new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png")));

         @Override
         protected void paintComponent(Graphics g) {
              super.paintComponent(g);
              g.drawImage(image, 0, 0, this);
         }
    });

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setVisible(true);
}

I am assuming that your Picture class has the following methods:

int getNumberOfPixels()
float getRValueOfNthPixel(int n)
float getGValueOfNthPixel(int n)
float getBValueOfNthPixel(int n)
void setRValueOfNthPixel(int n, float r)
void setGValueOfNthPixel(int n, float g)
void setBValueOfNthPixel(int n, float b)

If the number of pixels is always a multiple of 4, then one possible implementation of "specialEffect" method would be:

public void specialEffect() {
    int n = getNumberOfPixels();
    int limit1 = 1 * n / 4;
    int limit2 = 2 * n / 4;
    int limit3 = 3 * n / 4;
    int limit4 = 4 * n / 4;

    /*
     * The first loop is to apply an effect that removes the both the blue
     * and green component from each pixel leaving the red component
     * unchanged.
     */
    for (int i = 0; i < limit1; i++) {
        setBValueOfNthPixel(i, 0);
        setGValueOfNthPixel(i, 0);
    }

    /*
     * The next loop continuing from where the last left off is to remove
     * the blue and red component from each pixel leaving the green
     * component unchanged.
     */
    for (int i = limit1; i < limit2; i++) {
        setBValueOfNthPixel(i, 0);
        setRValueOfNthPixel(i, 0);
    }

    /*
     * The next loop continuing from where the last left off it to remove
     * the green and red component from each pixel leaving the blue 
     * component unchanged.
     */
    for (int i = limit2; i < limit3; i++) {
        setGValueOfNthPixel(i, 0);
        setRValueOfNthPixel(i, 0);
    }

    /*
     * The final loop continuing from where the last off is to convert each
     * pixel to greyscale.
     */
    for (int i = limit3; i < limit4; i++) {
        float grayValue = (getRValueOfNthPixel(i)
                + getGValueOfNthPixel(i)
                + getBValueOfNthPixel(i)) / 3;
        setRValueOfNthPixel(i, grayValue);
        setGValueOfNthPixel(i, grayValue);
        setBValueOfNthPixel(i, grayValue);
    }
}