class ImageCreationExample {
  
    static Image createSampleImage() {
        // instantiate a new BufferedImage (subclass of Image) instance 
        BufferedImage img = new BufferedImage(640, 480, BufferedImage.TYPE_INT_ARGB);
        
        //draw something on the image
        paintOnImage(img);
        
        return img;
    }

    static void paintOnImage(BufferedImage img) {
        // get a drawable Graphics2D (subclass of Graphics) object 
        Graphics2D g2d = (Graphics2D) img.getGraphics();
        
        // some sample drawing
        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, 640, 480);
        g2d.setColor(Color.WHITE);
        g2d.drawLine(0, 0, 640, 480);
        g2d.drawLine(0, 480, 640, 0);
        g2d.setColor(Color.YELLOW);
        g2d.drawOval(200, 100, 240, 280);
        g2d.setColor(Color.RED);
        g2d.drawRect(150, 70, 340, 340);
        
        // drawing on images can be very memory-consuming
        // so it's better to free resources early
        // it's not necessary, though
        g2d.dispose();
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Image img = createSampleImage();
        ImageIcon icon = new ImageIcon(img);
        frame.add(new JLabel(icon));
        frame.pack();
        frame.setVisible(true);
    }
}

public static void saveImage(String destination) throws IOException {
    // method implemented in "Creating a simple image Programmatically and displaying it" example
    BufferedImage img = createSampleImage();

    // ImageIO provides several write methods with different outputs
    ImageIO.write(img, "png", new File(destination));
}

BufferedImage image = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);

//you don't have to use the Graphics object, you can read and set pixel color individually
for (int i = 0; i < 256; i++) {
    for (int j = 0; j < 256; j++) {
        int alpha = 255; //don't forget this, or use BufferedImage.TYPE_INT_RGB instead
        int red = i; //or any formula you like
        int green = j; //or any formula you like
        int blue = 50; //or any formula you like
        int color = (alpha << 24) | (red << 16) | (green << 8) | blue;
        image.setRGB(i, j, color);
    }
}

ImageIO.write(image, "png", new File("computed.png"));

static void setupQualityHigh(Graphics2D g2d) {
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
    // many other RenderingHints KEY/VALUE pairs to specify
}


static void setupQualityLow(Graphics2D g2d) {
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_OFF);
    g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_SPEED);
}

int width = 256; //in pixels
int height = 256; //in pixels
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_4BYTE_ABGR);
//BufferedImage.TYPE_4BYTE_ABGR - store RGB color and visibility (alpha), see javadoc for more info

Graphics g = image.createGraphics();

//draw whatever you like, like you would in a drawComponent(Graphics g) method in an UI application
g.setColor(Color.RED);
g.fillRect(20, 30, 50, 50);

g.setColor(Color.BLUE);
g.drawOval(120, 120, 80, 40);

g.dispose(); //dispose graphics objects when they are no longer needed

//now image has programmatically generated content, you can use it in graphics.drawImage() to draw it somewhere else
//or just simply save it to a file
ImageIO.write(image, "png", new File("myimage.png"));

BufferedImage cat = ImageIO.read(new File("cat.jpg")); //read existing file

//modify it
Graphics g = cat.createGraphics();
g.setColor(Color.RED);
g.drawString("Cat", 10, 10);
g.dispose();

//now create a new image
BufferedImage cats = new BufferedImage(256, 256, BufferedImage.TYPE_4BYTE_ABGR);

//and draw the old one on it, 16 times
g = cats.createGraphics();
for (int i = 0; i < 4; i++) {
    for (int j = 0; j < 4; j++) {
        g.drawImage(cat, i * 64, j * 64, null);
    }
}

g.setColor(Color.BLUE);
g.drawRect(0, 0, 255, 255); //add some nice border
g.dispose(); //and done

ImageIO.write(cats, "png", new File("cats.png"));