Creating Images Programmatically

Remarks#

BufferedImage.getGraphics() always returns Graphics2D.

Using a VolatileImage may significantly improve the speed of drawing operations, but also has its drawbacks: its contents may be lost at any moment and they may have to be redrawn from scratch.

Creating a simple image programmatically and displaying it

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);
    }
}

Save an Image to disk

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));
}

Specifying image rendering quality

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);
}

A comparison of QUALITY and SPEED rendering of the sample image:

Creating an image with BufferedImage class

Editing and re-using image with BufferedImage

Setting individual pixel’s color in BufferedImage

How to scale a BufferedImage

 /**
 * Resizes an image using a Graphics2D object backed by a BufferedImage.
 * @param srcImg - source image to scale
 * @param w - desired width
 * @param h - desired height
 * @return - the new resized image
 */
private BufferedImage getScaledImage(Image srcImg, int w, int h){

    //Create a new image with good size that contains or might contain arbitrary alpha values between and including 0.0 and 1.0.
    BufferedImage resizedImg = new BufferedImage(w, h, BufferedImage.TRANSLUCENT);

    //Create a device-independant object to draw the resized image
    Graphics2D g2 = resizedImg.createGraphics();

    //This could be changed, Cf. https://stackoverflow.com/documentation/java/5482/creating-images-programmatically/19498/specifying-image-rendering-quality
    g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);

    //Finally draw the source image in the Graphics2D with the desired size.
    g2.drawImage(srcImg, 0, 0, w, h, null);

    //Disposes of this graphics context and releases any system resources that it is using
    g2.dispose();

    //Return the image used to create the Graphics2D 
    return resizedImg;
}