How to make smoother gradient background colors

Question

Using GradientPaint for gradient background colors is not always satisfactory, especially in certain sizes. For example this code:

public class TestPanel extends JPanel {

    protected void paintComponent( Graphics g ) {
        Graphics2D g2d = (Graphics2D) g;
        int w = getWidth();
        int h = getHeight();
        Color color1 = Color.BLACK;
        Color color2 = Color.GRAY;
        GradientPaint gp = new GradientPaint(0, 0, color1, 0, h, color2);
        g2d.setPaint(gp);
        g2d.fillRect(0, 0, w, h);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                TestPanel panel = new TestPanel();
                frame.add(panel);
                frame.setSize(200,200);
                frame.setLocationRelativeTo(null);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }
}

produces the following:

The cyclic version looks even worse than that:

How can I make the gradient look smoother (in both cases)?

EDIT:

It seems that it is (at least partially) a monitor problem. The gradient colors look awful on my netbook (1024 x 600, True Color 32-bit) while they look a lot better on my desktop pc (1280 x 1024, True Color 32-bit). But the results are still not so smooth even with the desktop's monitor.

Both are using Java Version 6 Update 33.

Does that mean that an application should only use gradient backgrounds when it is viewed with higher resolutions?

EDIT 2:

Anyway, for those facing simlar problem or are just interested in this, I think that the only solution for a gradient color to look smoother is just higher resolution (assuming that the monitor is already set to true color of course) - which is not really a solution. Like I said in a comment, I thought that a 1024 x 600 resolution would be sufficient for a simple black-to-gray gradient color but it seems that I was wrong. When the same code is run on a computer with a monitor that supports higher resolution the gradient looks better, like through my desktop's monitor, 1280 x 1024. Unfortunately I dont have an option for better resolution but I believe it would look even smoother. I also noticed that the two images that I uploaded (taken from my netbook) when they are viewed through a better monitor these same images look smoother... so it must be just the resolution.

Since there is no solution I think that the only way to use specific gradient steps that would always look smooth (like black-to-gray, which even that seems to look bad in lower resolutions) is to have the gui program test for resolution on start-up and make the choice to show the appropriate gradient but I'm not sure if it is worth it. And using less gradient steps is just a compromise.

Due to lack of more/better responses, I've accepted the use of pre-dithered images as an answer.

Answer 1

I see your images, but cannot reproduce the banding. Do you have your display set to TrueColor? Are you using a recent Java version? Anyway, the following line might help:

g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);

EDIT: it seems that dithering is not supported in Java for TrueColor gradients, even if you don't have enough shades of gray... Some ideas:

• use some colors
• use pre-dithered image files

http://en.wikipedia.org/wiki/Colour_banding

Answer 2

I can see it. I think it's because the panel's size and the number of colors don't match up. One way to make it smoother is to make the panel's size an even multiple of the number of colors in the gradient. It's not perfect, but I don't know a better way.

public class TestPanel extends JPanel {

    private static final int scale = 2;
    private static final Color c1 = Color.BLACK;
    private static final Color c2 = Color.GRAY;
    private static final int size = (c2.getRed() - c1.getRed()) * scale;

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(size, size);
    }

    @Override
    protected void paintComponent( Graphics g ) {
        Graphics2D g2d = (Graphics2D) g;
        int w = getWidth();
        int h = getHeight();
        GradientPaint gp = new GradientPaint(0, 0, c1, 0, h, c2);
        g2d.setPaint(gp);
        g2d.fillRect(0, 0, w, h);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPanel());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}