Graphics2D

Accessing Pixels

You can directly access the pixels of a Graphics object using the getRGB() and setRGB() methods.

Example with getRGB() and setRGB() (Run Applet)

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class GetAndSetPixelDemo extends JApplet
{
    @Override
    public void init()
    {
        this.setContentPane(new View());
    }

    public class View extends JPanel
    {
        @Override
        protected void paintComponent(Graphics g)
        {
            final BufferedImage bImg = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
            final Graphics2D g2d = bImg.createGraphics();

            g2d.setColor(Color.BLACK);
            g2d.drawString("setRGB() and getRGB() demo", 50, 30);

            int y;
            // write some pixels to red
            for (y = 50; y < 100; y++)
            {
                bImg.setRGB(50, y, (Color.RED).getRGB()); // we shall change this colour in a moment


                // set   some extra pixels to show that the pixels do get set to red
                bImg.setRGB(60, y, (Color.RED).getRGB()); // we do not change this colour
            }


            // read some pixels.
            // change them to black if they are currently red
            for (y = 50; y < 100; y++)
            {
                if (bImg.getRGB(50, y) == (Color.RED).getRGB()) // read the pixels colour
                {
                    bImg.setRGB(50, y, (Color.BLACK).getRGB()); // change the colour if it matches
                }


                // compare some pixels that are not red   to show that the if statement works
                if (bImg.getRGB(40, y) == (Color.RED).getRGB()) // read the pixels colour
                {
                    bImg.setRGB(40, y, (Color.BLACK).getRGB()); // change the colour if it matches
                }
            }


            g.drawImage(bImg, 0, 0, getWidth(), getHeight(), this);
        }
    }
}

Manipulating an Image's Pixels

The getRGB() and setRGB() methods store colour details as a 32 bit integer number, where bits 24-31 are alpha, 16-23 are red, 8-15 are green and 0-7 are blue. The example below shows how we can directly minipulate the alpha, red, green and blue components of a an images pixels.

Manipulating an Image's pixels example (Run Applet)

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class ManipulateImagePixelsDemo extends JApplet
{
    @Override
    public void init()
    {
        setContentPane(new View());
    }

    public class View extends JPanel
    {
        @Override
        protected void paintComponent(Graphics g)
        {
            // display two images over the total space of the applet's panel

            final Image gif = new ImageIcon(getClass().getClassLoader().getResource("images/koala.jpg")).getImage();
            final int gap = 10;  // gap between the two displayed images
            final int startX = 5;
            final int startY = 5;
            final int width = (this.getWidth() - 20) / 2;
            final int height = (this.getHeight() - 10);
            final BufferedImage bImg = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
            final Graphics2D g2d = bImg.createGraphics();

            g2d.setColor(Color.BLACK);
            g2d.drawImage(gif, startX, startY, width, height, this);

            for (int x = startX; x < startX + width; x++)
            {
                for (int y = startY; y < startY + height; y++)
                {
                    int pixelColour;
                    int alpha;
                    int red;
                    int green;
                    int blue;
                    // get the pixel's colour as an integer
                    pixelColour = bImg.getRGB(x, y);

                    // extract the alpha, red, green and blue colour data from the pixel's RGB colour
                    alpha = (pixelColour >> 24) & 0xff;
                    red = (pixelColour >> 16) & 0xff;
                    green = (pixelColour >> 8) & 0xff;
                    blue = (pixelColour) & 0xff;

                    // manipulate the pixel by writting back only the blue component of the RGB colour
                    bImg.setRGB(x, y, new Color(0, 0, blue, alpha).getRGB());

                    // manipulate the pixel by adjusting its alpha value
                    bImg.setRGB(x + width + gap, y, new Color(red, green, blue, alpha / 4).getRGB());
                }
            }

            // draw to the graphic g
            g.drawImage(bImg, 0, 0, getWidth(), getHeight(), this);
        }
    }
}