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Is it possible to give AWT applications sharp taskbar icons in Windows 10

I'm trying to set the icon of a Java AWT application so it renders in native resolution on the Windows 10 taskbar (including when desktop scaling is set above 100%). It seems that by default, if an executable embeds an icon containing multiple sizes, Windows seems to pick a size larger than the actual size of taskbar icons and downsize it (at 100% scale it resizes the 32 pixel icon to 24, even if a 24 pixel icon is supplied, and similarly for other scales.)
I've solved this problem for C++ MFC applications by loading just the correctly sized icon as a resource and sending a WM_SETICON message to the window, which results in a nice sharp icon on the taskbar and alt-tab dialog.
smallIcon = (HICON)LoadImage( myInstance, MAKEINTRESOURCE(smallIconRes), IMAGE_ICON, smallIconSize, smallIconSize, LR_DEFAULTCOLOR );
SendMessage(hWnd, WM_SETICON, ICON_SMALL, (LPARAM)smallIcon);
bigIcon = (HICON)LoadImage( myInstance, MAKEINTRESOURCE(bigIconRes), IMAGE_ICON, bigIconSize, bigIconSize, LR_DEFAULTCOLOR );
SendMessage(hWnd, WM_SETICON, ICON_BIG, (LPARAM)bigIcon);
That approach doesn't seem to work for Java applications - a WM_SETICON message with wParam set to ICON_SMALL works fine, but the equivalent with ICON_BIG is ignored.
If I try to use Java's API to set the icon, by doing this
List<Image> icons = new ArrayList<Image>();
icons.add(windowIcons.getIcon(20)); // small icons are 20x20 pixels
icons.add(windowIcons.getIcon(30)); // large are 30x30 at 125% scale
setIconImages(icons);
the correct icon is used but it appears blurry, as if something has resized it to the "expected" size and then resized it back. Left here is how it appears, right is the contents of the icon file.
So, my question is: what can I do in this Java application to make Windows render the icon I give it on the taskbar without scaling it and blurring the details?

There is indeed a scaling function called getScaledIconImage() in sun.awt.SunToolkit which is is always used when setting the icons. You must bypass this function in order to get an unaliased icon. So what you need is a replacement for java.awt.Window.setIconImages() method.
Provided several icon images Icon16x16.png, Icon24x24.png, etc. This is an example of a customSetIconImages() which puts a crisp 24x24 pixels icon in the taskbar of Windows 10.
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.ImageIcon;
import java.awt.peer.WindowPeer;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
#SuppressWarnings("serial")
public class MyFrame extends Frame implements WindowListener {
final Image i16, i24, i32, i48;
MyFrame() throws Exception {
i16 = Toolkit.getDefaultToolkit().getImage("Icon16x16.png");
i24 = Toolkit.getDefaultToolkit().getImage("Icon24x24.png");
i32 = Toolkit.getDefaultToolkit().getImage("Icon32x32.png");
i48 = Toolkit.getDefaultToolkit().getImage("Icon48x48.png");
addWindowListener(this);
setSize(500,300);
setTitle("Unaliased icon example");
setLayout(new FlowLayout());
setVisible(true);
}
public synchronized void customSetIconImages(java.util.List<Image> icons) throws Exception {
Field windowIcons = Class.forName("java.awt.Window").getDeclaredField("icons");
windowIcons.setAccessible(true);
windowIcons.set(this, new ArrayList<Image>(icons));
if (getPeer() != null)
updateIconImages(i24, 24, 24, i24, 24, 24);
firePropertyChange("iconImage", null, null);
}
public void updateIconImages(Image big, int bw, int bh, Image small, int sw, int sh) throws Exception {
DataBufferInt iconData = getUnscaledIconData(big, bw, bh);
DataBufferInt iconSmData = getUnscaledIconData(small, sw, sh);
WindowPeer peer = (WindowPeer) getPeer();
Method setIconImagesData = Class.forName("sun.awt.windows.WWindowPeer").getDeclaredMethod("setIconImagesData", int[].class, int.class, int.class, int[].class, int.class, int.class);
setIconImagesData.setAccessible(true);
setIconImagesData.invoke(peer, iconData.getData(), bw, bh, iconSmData.getData(), sw, sh);
}
public static DataBufferInt getUnscaledIconData(Image image, int w, int h) {
Image temporary = new ImageIcon(image).getImage();
BufferedImage buffImage = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2d = buffImage.createGraphics();
g2d.drawImage(temporary, 0, 0, null);
g2d.dispose();
Raster raster = buffImage.getRaster();
DataBuffer buffer = raster.getDataBuffer();
return (DataBufferInt) buffer;
}
#Override
public void windowOpened(WindowEvent arg0) {
try {
customSetIconImages(Arrays.asList(i24));
} catch (Exception e) {
System.err.println(e.getClass().getName()+" "+e.getMessage());
}
}
#Override
public void windowActivated(WindowEvent arg0) {
}
#Override
public void windowClosed(WindowEvent arg0) {
}
#Override
public void windowClosing(WindowEvent arg0) {
dispose();
}
#Override
public void windowDeactivated(WindowEvent arg0) {
}
#Override
public void windowDeiconified(WindowEvent arg0) {
}
#Override
public void windowIconified(WindowEvent arg0) {
}
public static void main(String args[]) throws Exception {
MyFrame fr = new MyFrame();
}
}
As #df778899 said, inside sun.awt.windows.WWindowPeer there are four private native methods which you can call t determine system icons size. You can combine the information returned by these methods with your own version getScaledIconImage() that performs unaliasing or not as yoou wish.
Last, note that this is a very dirty hack just for getting an unaliased icon. I've only tested in in Java 8 and Windows 10. And there are high chances that it doesn't work in newer versions of Java.

This won't be the answer you're hoping for, but this looks like a problem at the JDK level.
The window icons are handled by the sun.awt.windows.WWindowPeer class, which in turn makes a few native method calls, but there is enough to see in the source for this to point to the problem. Please read the important bit here.
Essentially, regardless of how many icon image sizes are provided, it will only pick out two sizes - for the WWindowPeer.getSysIconWidth() and getSysSmIconWidth() - to pass into the native setIconImagesData() method.
The getSysIconWidth() and getSysSmIconWidth() methods are also native, but it is possible to directly check their return values:
JFrame frame = new JFrame();
runOnPeer(frame, "getSysIconWidth");
runOnPeer(frame, "getSysIconHeight");
runOnPeer(frame, "getSysSmIconWidth");
runOnPeer(frame, "getSysSmIconHeight");
private void runOnPeer(JFrame frame, String methodName) {
//JDK8 style
//ComponentPeer peer = frame.getPeer();
//JDK11 style
Field peerField = Component.class.getDeclaredField("peer");
peerField.setAccessible(true);
Object peer = peerField.get(frame);
Method method = Class.forName("sun.awt.windows.WWindowPeer")
.getDeclaredMethod(methodName);
method.setAccessible(true);
System.out.println(methodName + "()=" + method.invoke(peer));
}
... which returns this on Windows 10 ...
getSysIconWidth()=32
getSysIconHeight()=32
getSysSmIconWidth()=16
getSysSmIconHeight()=16
As you say, clearly one of these image sizes is then being scaled for the taskbar.

HiDPI support with java 9+, scalling issue with JTable gridlines with Windows L&F - but not Nimbus

I'm migrating my Swing app to Java 11 to take advantage of the HiDPI display support. I'm using a Samsung monitor with resolution set to 3840x2160, scaling at 125%, with Windows 10.
Although java 9 and above are advertised as properly handling HiDPI scaling, when displaying a simple JTable, the gridlines appear of different thickness, as shown here:
Here's the code for this:
import javax.swing.*;
public class TestTable {
public static void main(String[] args) {
new TestTable();
}
public TestTable() {
JTable table = new JTable(12,6);
JDialog dialog = new JDialog();
JScrollPane sp = new JScrollPane(table);
table.setShowGrid(true);
table.setRowHeight(25);
dialog.setContentPane(sp);
dialog.setSize(300,300);
dialog.setVisible(true);
dialog.setLocationRelativeTo(null);
}
}
However, when setting the Nimbus L&F, the problem goes away:
import javax.swing.*;
public class TestTable {
public static void main(String[] args) {
try {
for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (Exception e) { }
new TestTable();
}
public TestTable() {
JTable table = new JTable(12,6);
JDialog dialog = new JDialog();
JScrollPane sp = new JScrollPane(table);
table.setShowGrid(true);
table.setRowHeight(25);
dialog.setContentPane(sp);
dialog.setSize(300,300);
dialog.setVisible(true);
dialog.setLocationRelativeTo(null);
}
}
How can I achieve the same with the default Windows L&F ?
(Same behavior is observed with java 9 & 10)

The difference is how the two look and feels render their grid lines.
The default look and feel MetalLookAndFeel (and the WindowsLookAndFeel) is based around BasicLookAndFeel which uses the BasicTableUI class to render the JTable. In BasicTableUI.paintGrid() it calls such as SwingUtilities2.drawHLine() - which actually calls Graphics.fillRect() which is the problem.
The Nimbus look and feel uses the SynthTableUI class. In SynthTableUI.paintGrid() it does ultimately call Graphics.drawLine(), which clearly draws a cleaner line under scaling.
As you say, that sounds like a bug in the main look and feels under HiDPI.
It is possible to create a workaround for this, though it's not particularly elegant.
With a custom version of the Graphics that is being used, it's possible to override fillRect() to use drawLine() instead, if the width or height is 1. This custom Graphics can be introduced specifically when painting the table:
JTable table = new JTable(12, 6) {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(new GraphicsWorkaround(g));
}
};
(An anonymous subclass is just used for brevity).
Then the GraphicsWorkaround class is written as a wrapper to the true g that was passed in. Subclassing DebugGraphics here is just a trick to save having to write delegate calls in all the other methods in Graphics:
import java.awt.Graphics;
import javax.swing.DebugGraphics;
public class GraphicsWorkaround extends DebugGraphics {
private final Graphics g;
public GraphicsWorkaround(Graphics g) {
super(g);
this.g = g;
}
#Override
public Graphics create() {
return new GraphicsWorkaround(g.create());
}
#Override
public void fillRect(int x, int y, int width, int height) {
if (width == 1)
g.drawLine(x, y, x, y + height - 1);
else if (height == 1)
g.drawLine(x, y, x + width - 1, y);
else
super.fillRect(x, y, width, height);
}
}
(The create() method is there to handle the internal scratchGraphics clone created in JComponent.paintComponent() ).
This then enables drawLine() to be called after all, which looked much better at 125% scaling.

Resize an image to fit the entirety of a JLabel adapting to its size

before you ask, I've looked up this issue in the website and the solutions provided have, unfortunately, not worked for me, so I must resort to asking it once more to see what could I be doing wrong.
Closest achievement I've had with the code I've got is this (I should most definitely use a try and catch when I retrieve the image, I'll save that for later on):
private void asignarTile(Tile tile, JPanel panel){
if(tile.getTipo() == 0){
ImageIcon ii = new ImageIcon("pasto.png");
Image image = ii.getImage();
Image newimg = image.getScaledInstance(32, 32, java.awt.Image.SCALE_SMOOTH);
ii = new ImageIcon(newimg);
tile.setIcon(ii);
panel.add(tile);
}
}
Now, as oblivious as it is, I must mention that the code does work for a specific size, but it won't adapt the size of the image to the JLabel afterwards, that means that first I'll have this:
But after I resize it I'll have this:
I think it would be useful to note that Tile extends JLabel, and these are the changes (columna means column, fila means row, maybe I should start writing my code entirely in english)
package gui;
import javax.swing.JLabel;
public class Tile extends JLabel{
private int fila, columna, tipo;
public int getFila() {
return fila;
}
public void setFila(int x) {
this.fila = x;
}
public int getColumna() {
return columna;
}
public void setColumna(int y) {
this.columna = y;
}
public int getTipo(){
return tipo;
}
public void setTipo(int tipo){
if(tipo >= 0 || tipo <= 6)
this.tipo = tipo;
}
public Tile(int x, int y, int tipo) {
this.setFila(x);
this.setColumna(y);
this.setTipo(tipo);
}
}
As a conclusion I must say that I have considered adding a componentListener to the Tile since it extends a JLabel, but I have also tried to resize the image to the label's dimensions to no avail, as it gave me an exception saying that its dimensions were 0, and well, they can't be 0.
Thank you for reading!

You can try Darryl's Stretch Icon for dynamic resizing.
Otherwise you would extend JComponent (instead of JLabel) and do you own custom painting of the image. See Background Panel for an example of how to paint a scaled image.

I would recommend that you try to create or find a larger tile image. If you try to stretch the image, you will degrade it, but this is not so for shrinking.

This code looks good.
Here's a code review suggestion:
The serializable class Tile.java does not declare a static final serialVersionUID field of type long. Solution: Add a generated serial version ID to the selected type.

Java Swing - place image in JLabel to/above second JLabel (map, player indicator)

I have a JFrame window with GridBagLayout(). There is a JLabel with Icon - it's a map. Now I need to show another picture (player position indicator) above map.
Is it possible, how?
Thank you very much!

Subclass JLabel and override the paint method.
public void paintComponent(Graphics g) {
super.paintComponent(g);
// paint player location on map
}
Handle your conversion from in game coordinates to coordinates on the map.

As an alternative to paintComponent(), you might also want to look at OverlayLayout, seen here. For some reason it's not included in the gallery, but it may be of use.

Couldn't resist to take this question as an opportunity to play with new jdk7 api :-)
Override paintComponent definitely is a good solution. Nevertheless, it requires subclassing just to paint something at a given location on top of something else. The ol' way doing so would be a JLayeredPane (which is a pain to handle). The new jdk has a JLayer component which allows to do that (and a lot more) by simple decoration of the component. Here's a snippet which:
has a label with the base image and decorates it with the default JLayer
adds the "player" image to the layer's glassPane
uses Rob's DragLayout (set on the glassPane) to move the player around, bare bones ui with two sliders
Working code (just some outer boiler plate missing, you all have your templates to stick that in :)
// to please Andrew :)
JLabel fooLabel = new JLabel(new ImageIcon(ImageIO.read(
new URL("http://pscode.org/media/stromlo2.jpg"))));
final JLayer<JLabel> layer = new JLayer<JLabel>(fooLabel);
final JLabel player = new JLabel(new CursorIcon(30));
// to please myself (never-ever use a null layout :)
layer.getGlassPane().setLayout(new DragLayout());
layer.getGlassPane().add(player);
layer.getGlassPane().setVisible(true);
final JSlider horizontal = new JSlider(0, fooLabel.getPreferredSize().width, 0);
final JSlider vertical = new JSlider(JSlider.VERTICAL, 0, fooLabel.getPreferredSize().height, 0);
vertical.setInverted(true);
ChangeListener l = new ChangeListener() {
#Override
public void stateChanged(ChangeEvent e) {
player.setLocation(horizontal.getValue(), vertical.getValue());
layer.revalidate();
}
};
horizontal.addChangeListener(l);
vertical.addChangeListener(l);
Quick icon:
public static class CursorIcon implements Icon {
private int size;
public CursorIcon(int size) {
this.size = size;
}
#Override
public void paintIcon(Component c, Graphics g, int x, int y) {
g.setColor(Color.red);
g.drawLine(size/2,y,size/2,size);
g.drawLine(x,size/2,size,size/2);
}
#Override
public int getIconWidth() {
return size;
}
#Override
public int getIconHeight() {
return size;
}
}
For earlier jdk versions, the SwingLabs subproject JXLayer is available

Creating custom JButton from images containing transparent pixels

Read edit 2 for what I'm actually missing to make it work
I'm currently trying to create some custom JButtons using images created in photoshop that have an alpha parameter.
So far, overriding the paint() method to draw the image has worked in the sense that the button is drawn showing the correct image. I'd like to improve it, though, by making its shape (clickable area) the same as the visible pixels on the image (right now if I draw the button's border, it's a square).
Is there an easy way to do that or do I have to parse the image and find the alpha pixels to make a custom border?
Which methods would I have to override to make it work the way I want?
Also, another question I'm going to have later: would it be better to use some kind of algorithm to change the images' colors to make it seem like it is being clicked when people click on it or am I better off creating a second image and drawing that one while the button is active?
Edit: I just read on some other question that I should redefine paintComponent() instead of paint(), I'd like to know why since redefining paint() works fine?
Edit 2: I changed everything to make sure my JButtons are created using the default constructor with an icon. What I'm trying to do is get the X and Y position of where the click was registered and grab the icon's pixel at that position and check its alpha channel to see if it is 0 (if it is, do nothing, else do the action it is supposed to do).
The thing is, the alpha channel always returns 255 (and blue, red and green are at 238 on transparent pixels). On other pixels, everything returns the value it should be returning.
Here's an example (try it with another image if you want) that recreates my problem:
public class TestAlphaPixels extends JFrame
{
private final File FILECLOSEBUTTON = new File("img\\boutonrondX.png"); //My round button with transparent corners
private JButton closeButton = new JButton(); //Creating it empty to be able to place it and resize the image after the button size is known
public TestAlphaPixels() throws IOException
{
setLayout(null);
setSize(150, 150);
closeButton.setSize(100, 100);
closeButton.setContentAreaFilled(false);
closeButton.setBorderPainted(false);
add(closeButton);
closeButton.addMouseListener(new MouseListener()
{
public void mouseClicked(MouseEvent e)
{
}
public void mousePressed(MouseEvent e)
{
}
public void mouseReleased(MouseEvent e)
{
System.out.println("Alpha value of pixel (" + e.getX() + ", " + e.getY() + ") is: " + clickAlphaValue(closeButton.getIcon(), e.getX(), e.getY()));
}
public void mouseEntered(MouseEvent e)
{
}
public void mouseExited(MouseEvent e)
{
}
});
Image imgCloseButton = ImageIO.read(FILECLOSEBUTTON);
//Resize the image to fit the button
Image newImg = imgCloseButton.getScaledInstance((int)closeButton.getSize().getWidth(), (int)closeButton.getSize().getHeight(), java.awt.Image.SCALE_SMOOTH);
closeButton.setIcon(new ImageIcon(newImg));
}
private int clickAlphaValue(Icon icon, int posX, int posY)
{
int width = icon.getIconWidth();
int height = icon.getIconHeight();
BufferedImage tempImage = (BufferedImage)createImage(width, height);
Graphics2D g = tempImage.createGraphics();
icon.paintIcon(null, g, 0, 0);
g.dispose();
int alpha = (tempImage.getRGB(posX, posY) >> 24) & 0x000000FF;
return alpha;
}
public static void main(String[] args)
{
try
{
TestAlphaPixels testAlphaPixels = new TestAlphaPixels();
testAlphaPixels.setVisible(true);
testAlphaPixels.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
catch(IOException ioe)
{
ioe.printStackTrace();
}
}
}
This is just a wild guess, but is it possible that when my image gets cast to an Icon, it loses its Alpha property and thus doesn't return the correct value? Anyway, I'd really appreciate it if someone could actually help me out and tell me what I should be changing to get the correct value.
I'm guessing that because when I try it with the original image, the alpha channel's value is fine, but I can't actually use that BufferedImage because I resize it, so I actually get the channel values of the image with the original size...

I think you are on the wrong way. You do not have to override neither paint() nor paintComponent() methods. JButton already "knows" to be shown with image only:
ImageIcon cup = new ImageIcon("images/cup.gif");
JButton button2 = new JButton(cup);
See the following tutorial for example: http://www.apl.jhu.edu/~hall/java/Swing-Tutorial/Swing-Tutorial-JButton.html
Moreover swing is fully customized. You can control opacity, border, color etc. You probably should override some mentioned methods to change functionality. But in most cases there is better and simpler solution.

Since there were good elements in multiple answers, but none of the answers were complete on their own, I'll answer my own question so other people that have the same problem can try something similar.
I created my buttons using a new class which extends JButton, with a new constructor that takes a BufferedImage as parameter instead of an icon. The reason for that is that when I did something like myButton.getIcon(), it would return an Icon, then I'd have to make various manipulations on it to make it a BufferedImage of the right size, and it ended up not working anyway because it seems like the first cast to Icon made it lose the alpha data in the pixels, so I couldn't check to see if the user was clicking on transparent pixels or not.
So I did something like this for the constructor:
public class MyButton extends JButton
{
private BufferedImage bufImg;
public MyButton(BufferedImage bufImg)
{
super(new ImageIcon(bufImg));
this.bufImg = bufImg;
}
}
Then I created an accessor for my bufImg that resized the image to fit the JButton using the getSize() method and then returned an image resized at the right size. I do the transformations in the getBufImg() accessor because the image size might change when the window gets resized. When you call the getBufImg(), it's usually because you clicked on the button and thus you're not currently resizing the window.
Something a little bit like this will return the image at the right size:
public BufferedImage getBufImg()
{
BufferedImage newImg = new BufferedImage(getSize().getWidth(), getSize().getHeight(), BufferedImage.TYPE_INT_ARGB); //Create a new buffered image the right size
Graphics2D g2d = newImg.createGraphics();
g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
g2d.drawImage(bufImg, 0, 0, getSize().getWidth(), getSize().getHeight(), null);
g2d.dispose();
return newImg;
}
With that buffered image, you can then code a method like this:
private int clickAlphaValue(BufferedImage bufImg, int posX, int posY)
{
int alpha;
alpha = (bufImg.getRGB(posX, posY) >>24) & 0x000000FF; //Gets the bit that contains alpha information
return alpha;
}
That you call on the button that implements a MouseListener, like this:
myButton.addMouseListener(new MouseListener()
{
public void mouseClicked(MouseEvent e)
{
}
public void mousePressed(MouseEvent e)
{
}
public void mouseReleased(MouseEvent e)
{
if(clickAlphaValue(((myButton)e.getSource()).getBufImg(), e.getX(), e.getY()) != 0) //If alpha is not set to 0
System.exit(0); //Or other things you want your button to do
}
public void mouseEntered(MouseEvent e)
{
}
public void mouseExited(MouseEvent e)
{
}
});
And voila! The button will only do the action if you clicked on non-transparent pixels.
Thanks for the help everyone, I couldn't have come up with this solutions on my own.

If you want to have shape-specific click points, you're better off using Shape and their contains method. If you want, you can create a shape when creating your custom button class as part of it, and implement a contains method by wrapping around the shape's contains method.
As for the custom JButton, create a class that extends JButton, like this:
import java.awt.*;
import javax.swing.*;
public class CustomButton extends JButton{
/** Filename of the image to be used as the button's icon. */
private String fileName;
/** The width of the button */
private int width;
/** The height of the button. */
private int height;
public CustomButton(String fileName, int width, int height){
this.fileName = fileName;
this.width = width;
this.height = height;
createButton();
}
/**
* Creates the button according to the fields set by the constructor.
*/
private void createButton(){
this.setIcon(getImageIcon(filename));
this.setPreferredSize(new Dimension(width, height));
this.setMaximumSize(new Dimension(width, height));
this.setFocusPainted(false);
this.setRolloverEnabled(false);
this.setOpaque(false);
this.setContentAreaFilled(false);
this.setBorderPainted(false);
this.setBorder(BorderFactory.createEmptyBorder(0,0,0,0));
}
}
Here's how you can load the ImageIcon, if you want to do it like this.
public ImageIcon getImageIcon(String fileName){
String imageDirectory = "images/"; //relative to classpath
URL imgURL = getClass().getResource(imageDirectory + fileName);
return new ImageIcon(imgURL);
}
This will give you a button that will at least look like your image.
I asked a similar question regarding Image-based events on click, and Shapes helped wonders.
I guess it comes down to how complex your button images are.
Here's reference anyway:
How can you detect a mouse-click event on an Image object in Java?
PS: Maybe look into generating shapes from images, that go around all the pixels that aren't transparent. No idea if this is possible, but it would mean that a button would only be "pressed" if the user clicks on the image part of it. Just a thought.

If you want your button layout to be that of the non-transparent pixels in your image, then you should redefine the paintComponent() method. It is the most correct way of doing it (overriding paint() worked in old times but is now discouraged).
However I think it is not exactly what you want: you want a click on the button to be detected only if it is on a non-transparent pixel, right? In that case you have to parse your image and when clicked compare mouse coordinates to the pixel alpha channel of your image as JButton does not have such a feature.

If you have a round button, this is exactly what you need:
public class RoundButton extends JButton {
public RoundButton() {
this(null, null);
}
public RoundButton(Icon icon) {
this(null, icon);
}
public RoundButton(String text) {
this(text, null);
}
public RoundButton(Action a) {
this();
setAction(a);
}
public RoundButton(String text, Icon icon) {
setModel(new DefaultButtonModel());
init(text, icon);
if(icon==null) return;
setBorder(BorderFactory.createEmptyBorder(0,0,0,0));
setContentAreaFilled(false);
setFocusPainted(false);
initShape();
}
protected Shape shape, base;
protected void initShape() {
if(!getBounds().equals(base)) {
Dimension s = getPreferredSize();
base = getBounds();
shape = new Ellipse2D.Float(0, 0, s.width, s.height);
}
}
#Override public Dimension getPreferredSize() {
Icon icon = getIcon();
Insets i = getInsets();
int iw = Math.max(icon.getIconWidth(), icon.getIconHeight());
return new Dimension(iw+i.right+i.left, iw+i.top+i.bottom);
}
#Override public boolean contains(int x, int y) {
initShape();
return shape.contains(x, y);
//or return super.contains(x, y) && ((image.getRGB(x, y) >> 24) & 0xff) > 0;
}
}
JButton has a contains() method. Override it and call it on mouseReleased();

paintComponent() instead of paint() depends if you paint() inside XxxButtonUI or just override paintComponent(), but there exists the option JButton#setIcon.