I want to export an image painted on a canvas to a PNG or JPEG file. I found solutions that allow me to export the whole JPanel, but that's not what I want. When I try to export the canvas, the image I get has the right size but is completely black.

Here is my code:

public void exportImage(String imageName) {
    BufferedImage image = new BufferedImage(canvas.getWidth(), canvas.getHeight(), BufferedImage.TYPE_INT_RGB);
    Graphics2D graphics = (Graphics2D) canvas.getGraphics();
    paint(graphics);
    graphics.dispose();
    try {
        System.out.println("Exporting image: " + imageName);
        FileOutputStream out = new FileOutputStream(imageName);
        ImageIO.write(image, "png", out);
        out.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Edit:

This is my program

And this is the canvas that should be exported