Looking for the brighter red pixel of an image

Question

Hi, I need to find the brighter red pixel of an image. I tried this code, but the value of each pixel seemed to be the same (zero).
public static void findBrighterRedPoint(Image i, ImageObserver o){
     int redMax = 0; //0 to 255
     int xMax = 0;
     int yMax = 0;
     PixelGrabber pg = new PixelGrabber(i,0,0,i.getWidth(o),i.getHeight(o),true);
     ColorModel cm = pg.getColorModel();
     for(int a=0;a<pg.getHeight();a++){
          for(int c=0;c<pg.getWidth();c++){
               if(cm.getRed(((a-1)*pg.getWidth()+c)) > redMax){
                    redMax = cm.getRed(((a-1)*pg.getWidth()+c));
                    xMax=c;
                    yMax=a;
               if(f==(pg.getHeight()-1) && c==(pg.getWidth()-1)){
               System.out.println("Red bound max value: "+cm.getRed(((a-1)*pg.getWidth()+c))+" Arrow: "+a+" Collumn: "+c);
}//method endThanks for some help...
Edited by: juanma268 on Jul 25, 2008 5:45 PM

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;
public class LookingForRed extends MouseMotionAdapter {
    JLabel red, green, blue;
    BufferedImage image;
    public void mouseMoved(MouseEvent e) {
        Point p = e.getPoint();
        int rgb = image.getRGB(p.x, p.y);
        red.setText(String.valueOf(  (rgb >> 16)&0xff));
        green.setText(String.valueOf((rgb >>  8)&0xff));
        blue.setText(String.valueOf( (rgb >>  0)&0xff));
    public static void findBrighterRedPoint(Image i, ImageObserver o){
        int redMax = 0; //0 to 255
        int xMax = 0;
        int yMax = 0;
        int w = i.getWidth(o);
        int h = i.getHeight(o);
        int[] pixels = new int[w*h];
        PixelGrabber pg = new PixelGrabber(i,0,0,w,h,pixels,0,w);
        try {
            pg.grabPixels();
        } catch(InterruptedException e) {
            System.out.println("interrupt");
        ColorModel cm = pg.getColorModel();
        for(int a=0;a<pg.getHeight();a++){
            for(int c=0;c<pg.getWidth();c++){
                int index = a*pg.getWidth()+c;
                int pixel = pixels[index];
                if(cm.getRed(pixel) > redMax){
                    redMax = cm.getRed(pixel);
                    xMax=c;
                    yMax=a;
                if(a==(pg.getHeight()-1) && c==(pg.getWidth()-1)){
                    System.out.println("Red bound max value: "+redMax+
                               " Arrow: "+yMax+" Collumn: "+xMax);
    private void showGUI(BufferedImage image) {
        this.image = image;
        ImageIcon icon = new ImageIcon(image);
        JLabel label = new JLabel(icon, JLabel.CENTER);
        label.addMouseMotionListener(this);
        JPanel panel = new JPanel(new GridBagLayout());
        panel.add(label, new GridBagConstraints());
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(panel);
        f.add(getLabelPanel(), "Last");
        f.setSize(300,300);
        f.setLocation(200,200);
        f.setVisible(true);
        findBrighterRedPoint(image, label);
    private JPanel getLabelPanel() {
        red = new JLabel();
        green = new JLabel();
        blue = new JLabel();
        Dimension d = new Dimension(45, 25);
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2,2,2,2);
        gbc.weightx = 1.0;
        addComponents("r =", red,   panel, gbc, d);
        addComponents("g =", green, panel, gbc, d);
        addComponents("b =", blue,  panel, gbc, d);
        return panel;
    private void addComponents(String s, JLabel jl, Container c,
                               GridBagConstraints gbc, Dimension d) {
        gbc.anchor = GridBagConstraints.EAST;
        c.add(new JLabel(s), gbc);
        jl.setPreferredSize(d);
        gbc.anchor = GridBagConstraints.WEST;
        c.add(jl, gbc);
    public static void main(String[] args) {
        LookingForRed test = new LookingForRed();
        BufferedImage image = test.makeImage();
        test.showGUI(image);
    private BufferedImage makeImage() {
        int w = 200, h = 200;
        int type = BufferedImage.TYPE_INT_RGB;
        BufferedImage image = new BufferedImage(w, h, type);
        int[] data = new int[w*h];
        int x = 3*w/4;
        int y = 3*h/4;
        System.out.println("Max red value should appear at " +
                           "x = " + x + "  y = " + y);
        int a = 255;
        for(int j = 0; j < h; j++) {
            int b = j*255/(h-1);
            for(int k = 0; k < w; k++) {
                int r = (j == y && k == x) ? 255 : 127;
                int g = k*255/(w-1);
                data[j*w + k] = ((a & 0xff) << 24) |
                                ((r & 0xff) << 16) |
                                ((g & 0xff) <<  8) |
                                ((b & 0xff) <<  0);
        image.setRGB(0,0,w,h,data,0,w);
        return image;
}