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